gen_statem: disambiguate module/macro intra-doc links

Reframe the module doc in the gen_server house style: lead with what a
process group is and when to reach for one, the auto-eviction-on-death
behaviour, groups-vs-registry, and a running-context note. Keep the
runnable example; add an ignored dispatch/worker-pool example.

Move implementation reasoning to where a maintainer stands: lock
discipline onto the ProcessGroups store, the eager-cleanup rationale onto
reap_group, the join finalize-race detail into join's body comment.

Drop all RFC references and the stray phase marker, and lead the public
read/select fn docs with what the caller gets. Demote the pub(crate)
assert_type intra-doc link in pick_as to plain code, clearing a
pre-existing broken-link warning.

.githooks/pre-commit

@@ -0,0 +1,8 @@
+#!/bin/sh
+# smarm pre-commit gate: clippy the library (src/) with warnings as errors.
+# unwrap_used / expect_used are denied (Cargo.toml [lints.clippy]): library
+# code must not hide a panic behind unwrap/expect. Tests/examples are not gated.
+set -eu
+[ -f "$HOME/.cargo/env" ] && . "$HOME/.cargo/env"
+cd "$(git rev-parse --show-toplevel)"
+cargo clippy --lib -- -D warnings

Cargo.toml

@@ -7,6 +7,15 @@ rust-version = "1.95"
 [lints.rust]
 unexpected_cfgs = { level = "warn", check-cfg = ["cfg(loom)"] }
 
+[lints.clippy]
+# Library code must never hide a panic behind unwrap/expect. Both are denied; an
+# intentional panic is written explicitly as `match { Err(e) => panic!(..) }`.
+# panic!/unreachable! are deliberately left un-linted as the blessed explicit
+# form. Enforced on the library target only (`cargo clippy --lib`); tests and
+# examples unwrap freely and are not gated.
+unwrap_used = "deny"
+expect_used = "deny"
+
 [features]
 default = ["rq-mutex"]
 smarm-trace = []

examples/gen_statem_expanded.rs

@@ -31,12 +31,12 @@
 //! Default build is clean and runs. A BREAK-CASE MENU at the bottom documents
 //! how to make each of the four guarantees fire.
 //!
-//! Run: `cargo run --example gen_statem_fused`
+//! Run: `cargo run --example gen_statem_expanded`
 
 #![deny(dead_code, unreachable_patterns)]
 
 use smarm::run;
-use smarm::gen_statem::{spawn, Cx, Machine, Reply, Resolution, GenStatemRef};
+use smarm::gen_statem::{spawn, Cx, Machine, Reply, Resolution, Step, GenStatemRef};
 
 // === user types ============================================================
 
@@ -50,6 +50,7 @@ enum Door {
 struct Data {
     enters: u32, // total state entries (incl. initial)
     pushes: u32, // times a push closed the door
+    knocks: u32, // knocks answered (a Locked knock is postponed, then counted)
 }
 
 enum Cast {
@@ -57,17 +58,24 @@ enum Cast {
     Pull,
     Lock,
     Unlock(u32), // carries a key
+    Knock,       // counted when the door is reachable; postponed while Locked
 }
 
 enum Call {
     GetState(Reply<Door>),
     GetEnters(Reply<u32>),
     GetPushes(Reply<u32>),
+    GetKnocks(Reply<u32>),
 }
 
 enum Ev {
     Cast(Cast),
     Call(Call),
+    // The runtime's internal events. `Info` is out-of-band (here unused, so
+    // `()`); `StateTimeout` / `Timeout` are timer fires the loop feeds back in.
+    Info(()),
+    StateTimeout,
+    Timeout(&'static str),
 }
 
 const CODE: u32 = 1234;
@@ -115,34 +123,62 @@ impl DoorSm {
     fn start(init: Door) -> GenStatemRef<DoorSm> {
         spawn(DoorSm {
             state: init,
-            data: Data { enters: 0, pushes: 0 },
+            data: Data { enters: 0, pushes: 0, knocks: 0 },
         })
     }
 
-    fn enter(&mut self, _cx: &mut Cx<Ev>) {
+    fn enter(&mut self, cx: &mut Cx<Ev>) {
         self.data.enters += 1;
+        // A state-timeout: an Open door auto-closes after a quiet window. The
+        // loop auto-resets it on any transition, so it fires only if the door is
+        // still Open when it elapses.
+        if self.state == Door::Open {
+            cx.state_timeout(std::time::Duration::from_millis(5));
+        }
     }
 }
 
 impl Machine for DoorSm {
     type Ev = Ev;
 
+    fn state_timeout_ev() -> Ev {
+        Ev::StateTimeout
+    }
+
+    fn timeout_ev(name: &'static str) -> Ev {
+        Ev::Timeout(name)
+    }
+
     fn on_start(&mut self, cx: &mut Cx<Ev>) {
         self.enter(cx);
     }
 
-    fn handle(&mut self, ev: Ev, cx: &mut Cx<Ev>) {
+    fn handle(&mut self, ev: Ev, cx: &mut Cx<Ev>) -> Step<Ev> {
         let prev = self.state;
 
-        // ---- the transition table -----------------------------------------
-        // This match is total over (Door, Ev). Read it as the declared graph:
-        // each `=> To(x)` is an edge, each `=> Unhandled` an explicit refusal.
+        // ---- phase 1: postpone routing (borrow-only) ----------------------
+        // A deferred event is handed back untouched for the loop's postpone
+        // queue; no handler code runs on it. Here: a knock at a locked door.
+        // (The macro emits this as a `match (state, &ev)` yielding a bool; the
+        // hand-written form can just test directly.)
+        if let (Door::Locked, Ev::Cast(Cast::Knock)) = (prev, &ev) {
+            return Step::Postponed(ev);
+        }
+
+        // ---- phase 2: the consuming transition table ----------------------
+        // Total over (Door, Ev). Read it as the declared graph: each `=> To(x)`
+        // is an edge, each `=> Unhandled` an explicit refusal. The postponed
+        // pair above reappears as `unreachable!` so the match stays total.
         let res: Resolution<Door> = match (self.state, ev) {
             // --- Open -------------------------------------------------------
             (Door::Open, Ev::Cast(Cast::Push)) => {
                 on_push(&mut self.data);
                 Resolution::To(Door::Closed)
             }
+            (Door::Open, Ev::Cast(Cast::Knock)) => {
+                self.data.knocks += 1;
+                Resolution::To(prev)
+            }
             (Door::Open, Ev::Cast(Cast::Pull | Cast::Lock | Cast::Unlock(_))) => {
                 Resolution::Unhandled
             }
@@ -150,12 +186,20 @@ impl Machine for DoorSm {
             // --- Closed -----------------------------------------------------
             (Door::Closed, Ev::Cast(Cast::Pull)) => Resolution::To(Door::Open),
             (Door::Closed, Ev::Cast(Cast::Lock)) => Resolution::To(Door::Locked),
+            (Door::Closed, Ev::Cast(Cast::Knock)) => {
+                self.data.knocks += 1;
+                Resolution::To(prev)
+            }
             (Door::Closed, Ev::Cast(Cast::Push | Cast::Unlock(_))) => Resolution::Unhandled,
 
             // --- Locked (branching row: handler picks within UnlockOutcome) -
             (Door::Locked, Ev::Cast(Cast::Unlock(key))) => {
                 Resolution::To(on_unlock(key).into())
             }
+            // Routed out in phase 1; listed only to keep this match total.
+            (Door::Locked, Ev::Cast(Cast::Knock)) => {
+                unreachable!("postponed event is replayed, not dispatched here")
+            }
             (Door::Locked, Ev::Cast(Cast::Push | Cast::Pull | Cast::Lock)) => {
                 Resolution::Unhandled
             }
@@ -173,17 +217,38 @@ impl Machine for DoorSm {
                 r.reply(self.data.pushes);
                 Resolution::To(prev)
             }
+            (_, Ev::Call(Call::GetKnocks(r))) => {
+                r.reply(self.data.knocks);
+                Resolution::To(prev)
+            }
+
+            // --- timeouts: an Open door auto-closes; others have none armed --
+            (Door::Open, Ev::StateTimeout) => Resolution::To(Door::Closed),
+            (_, Ev::StateTimeout) => Resolution::Unhandled,
+            (_, Ev::Timeout(name)) => {
+                // No named timeout is armed in this run; a real handler would
+                // dispatch on `name`. Acknowledge it to exercise the field.
+                let _ = name;
+                Resolution::Unhandled
+            }
+
+            // --- out-of-band info: silent drop (the gen_server default) ------
+            (_, Ev::Info(_)) => Resolution::Unhandled,
         };
 
         // ---- apply the resolution -----------------------------------------
         match res {
-            Resolution::To(s) if s == prev => {} // stay: no enter
+            Resolution::To(s) if s == prev => Step::Stayed, // stay: no enter
             Resolution::To(s) => {
                 self.state = s; // sole writer of the state cell
+                cx.__reset_state_timeout(); // auto-reset across transitions
                 self.enter(cx);
+                Step::Transitioned
+            }
+            Resolution::Unhandled => {
+                cx.on_unhandled();
+                Step::Stayed
             }
-            Resolution::Postpone => unreachable!("postpone is not generated yet"),
-            Resolution::Unhandled => cx.on_unhandled(),
         }
     }
 }
@@ -193,20 +258,29 @@ fn main() {
         let door = DoorSm::start(Door::Closed);
 
         door.send(Ev::Cast(Cast::Lock)).unwrap(); // Closed -> Locked
+        door.send(Ev::Cast(Cast::Knock)).unwrap(); // Locked: postponed (not yet counted)
         door.send(Ev::Cast(Cast::Push)).unwrap(); // Locked: Push invalid -> Unhandled
-        door.send(Ev::Cast(Cast::Unlock(0))).unwrap(); // Locked: wrong key -> stay
-        door.send(Ev::Cast(Cast::Unlock(CODE))).unwrap(); // Locked -> Closed
-        door.send(Ev::Cast(Cast::Pull)).unwrap(); // Closed -> Open
-        door.send(Ev::Cast(Cast::Push)).unwrap(); // Open  -> Closed (pushes=1)
+        door.send(Ev::Cast(Cast::Unlock(0))).unwrap(); // Locked: wrong key -> stay (knock still deferred)
+        door.send(Ev::Cast(Cast::Unlock(CODE))).unwrap(); // Locked -> Closed; deferred Knock replays here
+        door.send(Ev::Cast(Cast::Push)).unwrap(); // Closed: Push invalid -> Unhandled
+        door.send(Ev::Cast(Cast::Pull)).unwrap(); // Closed -> Open (arms 5ms auto-close)
+        door.send(Ev::Info(())).unwrap(); // out-of-band: silently dropped
+
+        // Wait past the auto-close window: the state-timeout fires and the door
+        // closes itself, with no further input. (`smarm::sleep` parks the actor
+        // without blocking a worker thread, so the timer wheel keeps turning.)
+        smarm::sleep(std::time::Duration::from_millis(40));
 
         let st = door.call(|r| Ev::Call(Call::GetState(r))).unwrap();
         let enters = door.call(|r| Ev::Call(Call::GetEnters(r))).unwrap();
         let pushes = door.call(|r| Ev::Call(Call::GetPushes(r))).unwrap();
+        let knocks = door.call(|r| Ev::Call(Call::GetKnocks(r))).unwrap();
 
-        println!("state={st:?} enters={enters} pushes={pushes}");
-        assert_eq!(st, Door::Closed);
+        println!("state={st:?} enters={enters} pushes={pushes} knocks={knocks}");
+        assert_eq!(st, Door::Closed); // auto-closed by the state-timeout
         assert_eq!(enters, 5); // Closed(start) + Locked + Closed + Open + Closed
-        assert_eq!(pushes, 1);
+        assert_eq!(pushes, 0); // no push ever closed it this run
+        assert_eq!(knocks, 1); // the locked-door knock, replayed once unlocked
         println!("ok");
     });
 }

examples/gen_statem_macro.rs

@@ -1,4 +1,4 @@
-//! The **same** machine as `examples/gen_statem_fused.rs`, written through the
+//! The **same** machine as `examples/gen_statem_expanded.rs`, written through the
 //! `gen_statem!` macro. Diff this file against that one to see exactly what the
 //! macro buys: every `// ===` section there that was boilerplate (the `Ev`
 //! enum, the `DoorSm` struct, `start`, the whole `Machine` impl, the `enter`
@@ -21,7 +21,7 @@ use smarm::gen_statem;
 use smarm::run;
 use smarm::gen_statem::Reply;
 
-// === user types (identical to gen_statem_fused.rs) =========================
+// === user types (identical to gen_statem_expanded.rs) =========================
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 enum Door {
@@ -33,6 +33,7 @@ enum Door {
 struct Data {
     enters: u32, // total state entries (incl. initial)
     pushes: u32, // times a push closed the door
+    knocks: u32, // knocks answered (a Locked knock is postponed, then counted)
 }
 
 enum Cast {
@@ -40,12 +41,14 @@ enum Cast {
     Pull,
     Lock,
     Unlock(u32), // carries a key
+    Knock,       // counted when the door is reachable; postponed while Locked
 }
 
 enum Call {
     GetState(Reply<Door>),
     GetEnters(Reply<u32>),
     GetPushes(Reply<u32>),
+    GetKnocks(Reply<u32>),
 }
 
 const CODE: u32 = 1234;
@@ -87,7 +90,7 @@ fn on_unlock(key: u32) -> UnlockOutcome {
 
 gen_statem! {
     machine: DoorSm { state: Door, data: Data };
-    event:   Ev { cast: Cast, call: Call };
+    event:   Ev { cast: Cast, call: Call, info: () };
 
     // You name the bindings the bodies use; the macro can't lend you its own
     // `self`/`cx` across macro hygiene. `data` = &mut Data, `prev` = current
@@ -100,15 +103,20 @@ gen_statem! {
 
     on Door::Open => {
         cast Cast::Push                            => { on_push(data); Door::Closed },
+        cast Cast::Knock                           => { data.knocks += 1; prev },
         cast Cast::Pull | Cast::Lock | Cast::Unlock(_) => unhandled,
     }
     on Door::Closed => {
         cast Cast::Pull                            => Door::Open,
         cast Cast::Lock                            => Door::Locked,
+        cast Cast::Knock                           => { data.knocks += 1; prev },
         cast Cast::Push | Cast::Unlock(_)          => unhandled,
     }
     on Door::Locked => {
         cast Cast::Unlock(key)                     => on_unlock(key), // branch -> UnlockOutcome
+        // A knock at a locked door waits: defer it until the door is reachable,
+        // where the replay counts it.
+        cast Cast::Knock                           => postpone,
         cast Cast::Push | Cast::Pull | Cast::Lock  => unhandled,
     }
 
@@ -117,35 +125,43 @@ gen_statem! {
         call Call::GetState(r)  => { r.reply(prev); prev },
         call Call::GetEnters(r) => { r.reply(data.enters); prev },
         call Call::GetPushes(r) => { r.reply(data.pushes); prev },
+        call Call::GetKnocks(r) => { r.reply(data.knocks); prev },
+        // This machine arms no timeouts, so refuse them everywhere. (Info has a
+        // built-in silent-drop default, so it needs no row.)
+        state_timeout          => unhandled,
+        timeout _              => unhandled,
     }
 }
 
 fn main() {
     run(|| {
-        let door = DoorSm::start(Door::Closed, Data { enters: 0, pushes: 0 });
+        let door = DoorSm::start(Door::Closed, Data { enters: 0, pushes: 0, knocks: 0 });
 
         door.send(Ev::Cast(Cast::Lock)).unwrap(); // Closed -> Locked
+        door.send(Ev::Cast(Cast::Knock)).unwrap(); // Locked: postponed (not yet counted)
         door.send(Ev::Cast(Cast::Push)).unwrap(); // Locked: Push invalid -> Unhandled
-        door.send(Ev::Cast(Cast::Unlock(0))).unwrap(); // Locked: wrong key -> stay
-        door.send(Ev::Cast(Cast::Unlock(CODE))).unwrap(); // Locked -> Closed
+        door.send(Ev::Cast(Cast::Unlock(0))).unwrap(); // Locked: wrong key -> stay (knock still deferred)
+        door.send(Ev::Cast(Cast::Unlock(CODE))).unwrap(); // Locked -> Closed; deferred Knock replays here
         door.send(Ev::Cast(Cast::Pull)).unwrap(); // Closed -> Open
         door.send(Ev::Cast(Cast::Push)).unwrap(); // Open  -> Closed (pushes=1)
 
         let st = door.call(|r| Ev::Call(Call::GetState(r))).unwrap();
         let enters = door.call(|r| Ev::Call(Call::GetEnters(r))).unwrap();
         let pushes = door.call(|r| Ev::Call(Call::GetPushes(r))).unwrap();
+        let knocks = door.call(|r| Ev::Call(Call::GetKnocks(r))).unwrap();
 
-        println!("state={st:?} enters={enters} pushes={pushes}");
+        println!("state={st:?} enters={enters} pushes={pushes} knocks={knocks}");
         assert_eq!(st, Door::Closed);
         assert_eq!(enters, 5); // Closed(start) + Locked + Closed + Open + Closed
         assert_eq!(pushes, 1);
+        assert_eq!(knocks, 1); // the locked-door knock, replayed once unlocked
         println!("ok");
     });
 }
 
 // ===========================================================================
 // BREAK-CASE MENU — the four guarantees, through the macro. Each fires exactly
-// as it does in the hand-written gen_statem_fused.rs.
+// as it does in the hand-written gen_statem_expanded.rs.
 //
 // 1. ORPHAN HANDLER (dead_code -> error):
 //      add `fn on_slam(_d: &mut Data) {}` and don't reference it.

src/actor.rs

@@ -93,8 +93,10 @@ pub fn take_last_outcome() -> Option<Outcome> {
 /// unwinding to cross the boundary, but `catch_unwind` here means unwinding
 /// never actually does.
 pub extern "C-unwind" fn trampoline() {
-    let b = CURRENT_ACTOR_BOX.with(|c| c.borrow_mut().take())
-        .expect("trampoline entered without a closure set");
+    let b = match CURRENT_ACTOR_BOX.with(|c| c.borrow_mut().take()) {
+        Some(b) => b,
+        None => panic!("smarm: trampoline entered without a closure set (core corrupt)"),
+    };
 
     let outcome = match panic::catch_unwind(panic::AssertUnwindSafe(b)) {
         Ok(())       => Outcome::Exit,

src/channel.rs

@@ -176,8 +176,10 @@ impl<T> Receiver<T> {
                 if g.senders == 0 {
                     return Err(RecvError);
                 }
-                let me = crate::actor::current_pid()
-                    .expect("recv() called outside an actor");
+                let me = match crate::actor::current_pid() {
+                    Some(me) => me,
+                    None => panic!("smarm: recv() called outside an actor"),
+                };
                 debug_assert!(
                     g.parked_receiver.is_none_or(|(p, _)| p == me),
                     "channel has more than one receiver"
@@ -191,7 +193,10 @@ impl<T> Receiver<T> {
             // Release the lock before parking — the unparker will need it.
             crate::scheduler::park_current();
             // Woken up — record it before looping to check the queue.
-            crate::te!(crate::trace::Event::RecvWake(crate::actor::current_pid().unwrap()));
+            crate::te!(crate::trace::Event::RecvWake(match crate::actor::current_pid() {
+                Some(p) => p,
+                None => panic!("smarm: RecvWake outside an actor (core corrupt)"),
+            }));
         }
     }
 
@@ -222,8 +227,10 @@ impl<T> Receiver<T> {
     where
         T: Send + 'static,
     {
-        let me = crate::actor::current_pid()
-            .expect("recv_timeout() called outside an actor");
+        let me = match crate::actor::current_pid() {
+            Some(me) => me,
+            None => panic!("smarm: recv_timeout() called outside an actor"),
+        };
 
         // Fast path + wait registration, one critical section.
         let epoch;
@@ -254,7 +261,10 @@ impl<T> Receiver<T> {
         crate::scheduler::insert_wait_timer(deadline, me, target, epoch);
 
         crate::scheduler::park_current();
-        crate::te!(crate::trace::Event::RecvWake(crate::actor::current_pid().unwrap()));
+        crate::te!(crate::trace::Event::RecvWake(match crate::actor::current_pid() {
+            Some(p) => p,
+            None => panic!("smarm: RecvWake outside an actor (core corrupt)"),
+        }));
         let mut g = self.inner.lock();
         if let Some(v) = g.queue.pop_front() {
             crate::preempt::note_message_received();
@@ -283,17 +293,23 @@ impl<T> Receiver<T> {
         loop {
             {
                 let mut g = self.inner.lock();
-                if let Some(i) = g.queue.iter().position(|v| pred(v)) {
+                if let Some(i) = g.queue.iter().position(&pred) {
                     // position() found it, so remove() returns Some.
                     crate::preempt::note_message_received();
-                    return Ok(g.queue.remove(i).unwrap());
+                    let v = match g.queue.remove(i) {
+                        Some(v) => v,
+                        None => panic!("smarm: channel queue.remove after position (logic bug)"),
+                    };
+                    return Ok(v);
                 }
                 if g.senders == 0 {
                     // Closed and nothing queued can ever match.
                     return Err(RecvError);
                 }
-                let me = crate::actor::current_pid()
-                    .expect("recv_match() called outside an actor");
+                let me = match crate::actor::current_pid() {
+                    Some(me) => me,
+                    None => panic!("smarm: recv_match() called outside an actor"),
+                };
                 debug_assert!(
                     g.parked_receiver.is_none_or(|(p, _)| p == me),
                     "channel has more than one receiver"
@@ -303,7 +319,10 @@ impl<T> Receiver<T> {
             }
             // Release the lock before parking — the unparker will need it.
             crate::scheduler::park_current();
-            crate::te!(crate::trace::Event::RecvWake(crate::actor::current_pid().unwrap()));
+            crate::te!(crate::trace::Event::RecvWake(match crate::actor::current_pid() {
+                Some(p) => p,
+                None => panic!("smarm: RecvWake outside an actor (core corrupt)"),
+            }));
         }
     }
 
@@ -316,9 +335,13 @@ impl<T> Receiver<T> {
         F: Fn(&T) -> bool,
     {
         let mut g = self.inner.lock();
-        if let Some(i) = g.queue.iter().position(|v| pred(v)) {
+        if let Some(i) = g.queue.iter().position(&pred) {
             crate::preempt::note_message_received();
-            return Ok(Some(g.queue.remove(i).unwrap()));
+            let v = match g.queue.remove(i) {
+                Some(v) => v,
+                None => panic!("smarm: channel queue.remove after position (logic bug)"),
+            };
+            return Ok(Some(v));
         }
         if g.senders == 0 {
             return Err(RecvError);
@@ -466,7 +489,10 @@ impl<T> Selectable for Receiver<T> {
 /// see [`try_select`] for the fallible form; channel-only selects cannot
 /// fail).
 pub fn select(arms: &[&dyn Selectable]) -> usize {
-    try_select(arms).expect("select(): fd arm failed to register (use try_select)")
+    match try_select(arms) {
+        Ok(i) => i,
+        Err(e) => panic!("smarm: select() fd arm failed to register (use try_select): {e}"),
+    }
 }
 
 /// [`select`], fallible: `Err` when an arm fails to register (only fd
@@ -476,7 +502,10 @@ pub fn select(arms: &[&dyn Selectable]) -> usize {
 /// one has been unregistered.
 pub fn try_select(arms: &[&dyn Selectable]) -> std::io::Result<usize> {
     assert!(!arms.is_empty(), "select() on an empty arm list");
-    let me = crate::actor::current_pid().expect("select() called outside an actor");
+    let me = match crate::actor::current_pid() {
+        Some(me) => me,
+        None => panic!("smarm: select() called outside an actor"),
+    };
     loop {
         let epoch = crate::scheduler::begin_wait();
         if let Some(i) = register_arms(me, epoch, arms)? {
@@ -626,8 +655,12 @@ pub fn select_timeout(
     arms: &[&dyn Selectable],
     timeout: std::time::Duration,
 ) -> Option<usize> {
-    try_select_timeout(arms, timeout)
-        .expect("select_timeout(): fd arm failed to register (use try_select_timeout)")
+    match try_select_timeout(arms, timeout) {
+        Ok(r) => r,
+        Err(e) => panic!(
+            "smarm: select_timeout() fd arm failed to register (use try_select_timeout): {e}"
+        ),
+    }
 }
 
 /// [`select_timeout`], fallible: `Err` when an arm fails to register
@@ -638,7 +671,10 @@ pub fn try_select_timeout(
     timeout: std::time::Duration,
 ) -> std::io::Result<Option<usize>> {
     assert!(!arms.is_empty(), "select_timeout() on an empty arm list");
-    let me = crate::actor::current_pid().expect("select_timeout() called outside an actor");
+    let me = match crate::actor::current_pid() {
+        Some(me) => me,
+        None => panic!("smarm: select_timeout() called outside an actor"),
+    };
     let epoch = crate::scheduler::begin_wait();
     if let Some(i) = register_arms(me, epoch, arms)? {
         return Ok(Some(i)); // ready now: the timer was never armed

src/context.rs

@@ -94,10 +94,28 @@ unsafe extern "C" fn switch_to_actor_asm() {
 }
 
 /// Resume the actor whose sp is in `ACTOR_SP`. Returns when the actor yields.
+///
+/// # Safety
+///
+/// The caller must be running on a scheduler thread with a valid actor stack
+/// pointer installed in `ACTOR_SP` — either by `init_actor_stack` (first
+/// resume) or by a prior `switch_to_scheduler` (subsequent resumes). Resuming
+/// with an unset or stale `ACTOR_SP` transfers control to an arbitrary address.
+/// Must not be called from within an actor (only the scheduler side may resume).
 pub unsafe fn switch_to_actor() {
     unsafe { switch_to_actor_asm() };
 }
 
+/// Yield from the running actor back to its scheduler thread. Returns when the
+/// actor is next resumed via [`switch_to_actor`].
+///
+/// # Safety
+///
+/// The caller must be running on an actor stack that was entered through
+/// [`switch_to_actor`], so that `SCHEDULER_SP` holds the live saved stack
+/// pointer of the scheduler side. Calling this from the scheduler thread, or
+/// before any actor has been resumed, transfers control to an arbitrary
+/// address.
 #[unsafe(naked)]
 pub unsafe extern "C" fn switch_to_scheduler() {
     core::arch::naked_asm!(

src/gen_server.rs

@@ -528,7 +528,10 @@ impl<G: GenServer> TimerHandle<G> {
     /// [`TimerId`] you can pass to `cancel`. Timer fires arrive before info and
     /// inbox messages.
     pub fn arm_after(&self, after: Duration, msg: G::Timer) -> TimerId {
-        let mut reg = self.reg.lock().unwrap();
+        let mut reg = match self.reg.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: gen_server reg lock poisoned (core corrupt): {e}"),
+        };
         let local = reg.mint();
         // The fire thunk carries the local id so the loop can retire the entry
         // on dispatch; `msg` is moved in (no `Clone` needed for one-shots).
@@ -552,7 +555,10 @@ impl<G: GenServer> TimerHandle<G> {
     where
         G::Timer: Clone,
     {
-        let mut reg = self.reg.lock().unwrap();
+        let mut reg = match self.reg.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: gen_server reg lock poisoned (core corrupt): {e}"),
+        };
         let local = reg.mint();
         // A live periodic must keep the system arm open so the next tick can be
         // re-armed; the first periodic installs the loop's re-arm sender.
@@ -577,7 +583,10 @@ impl<G: GenServer> TimerHandle<G> {
     /// stops re-arming: the entry is removed so the loop will not schedule
     /// another tick even if the pending one already escaped onto the channel.
     pub fn cancel(&self, id: TimerId) -> bool {
-        let mut reg = self.reg.lock().unwrap();
+        let mut reg = match self.reg.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: gen_server reg lock poisoned (core corrupt): {e}"),
+        };
         if let Some(sub) = reg.oneshots.remove(&id) {
             return cancel_timer(sub);
         }
@@ -587,7 +596,7 @@ impl<G: GenServer> TimerHandle<G> {
                 reg.rearm_tx = None;
             }
             debug_assert!(
-                reg.rearm_tx.is_some() == !reg.periodics.is_empty(),
+                reg.rearm_tx.is_some() != reg.periodics.is_empty(),
                 "rearm_tx must be Some iff periodics is non-empty"
             );
             return beat;
@@ -846,7 +855,10 @@ fn server_loop<G: GenServer>(
     impl<G: GenServer> Drop for Terminate<G> {
         fn drop(&mut self) {
             {
-                let mut reg = self.1.lock().unwrap();
+                let mut reg = match self.1.lock() {
+                    Ok(g) => g,
+                    Err(e) => panic!("smarm: gen_server reg lock poisoned (core corrupt): {e}"),
+                };
                 for (_, sub) in reg.oneshots.drain() {
                     cancel_timer(sub);
                 }
@@ -995,7 +1007,10 @@ fn server_loop<G: GenServer>(
                         // The one-shot fired: retire its registry entry so the
                         // live set tracks only still-pending timers, then
                         // dispatch.
-                        reg.lock().unwrap().oneshots.remove(&id);
+                        match reg.lock() {
+                            Ok(mut g) => { g.oneshots.remove(&id); }
+                            Err(e) => panic!("smarm: gen_server reg lock poisoned (core corrupt): {e}"),
+                        }
                         guard.0.handle_timer(msg);
                         reset_idle(&mut idle_deadline);
                     }
@@ -1006,16 +1021,20 @@ fn server_loop<G: GenServer>(
                         // so the period is measured from fire-handling and a
                         // handler that cancels stops the just-armed instance.
                         let msg = {
-                            let mut g = reg.lock().unwrap();
+                            let mut g = match reg.lock() {
+                                Ok(g) => g,
+                                Err(e) => panic!("smarm: gen_server reg lock poisoned (core corrupt): {e}"),
+                            };
                             let r = &mut *g;
                             if let Some(p) = r.periodics.get_mut(&id) {
                                 let every = p.every;
                                 let msg = (p.make)();
-                                let tx = r
-                                    .rearm_tx
-                                    .as_ref()
-                                    .expect("a live periodic keeps rearm_tx Some")
-                                    .clone();
+                                let tx = match r.rearm_tx.as_ref() {
+                                    Some(tx) => tx.clone(),
+                                    None => panic!(
+                                        "smarm: live periodic without rearm_tx (logic bug)"
+                                    ),
+                                };
                                 p.live = send_after_to(every, tx, Sys::Tick(id));
                                 Some(msg)
                             } else {

src/gen_statem.rs

@@ -14,13 +14,13 @@
 //! [`on_start`](Machine::on_start), then one [`handle`](Machine::handle) per
 //! inbox event — mirroring `gen_server`'s spawn/teardown idioms.
 //!
-//! The [`gen_statem!`](crate::gen_statem) macro is the authoring surface: it
+//! The [`gen_statem!`](crate::gen_statem!) macro is the authoring surface: it
 //! *generates* a `Machine` impl from per-state handler blocks. Edge-validity is
 //! not a separate check — it falls out of the generated total `match (state,
 //! event)` under denied lints (a forgotten or duplicated pair is a compile
 //! error), so no proc-macro is needed. See `examples/gen_statem_macro.rs` for
-//! the macro form and `examples/gen_statem_fused.rs` for the hand-written shape
-//! it expands to.
+//! the macro form and `examples/gen_statem_expanded.rs` for the hand-written
+//! shape it expands to.
 //!
 //! ## The unified event
 //!
@@ -38,19 +38,51 @@
 //! `gen_server` call round-trip, but with the reply handle riding *inside* the
 //! user's own event so a handler can answer it.
 //!
-//! [`Resolution::Postpone`] and the timeout arming on [`Cx`] are part of the
-//! type surface but are not yet wired up.
+//! ## Timeouts
+//!
+//! Two timeout flavours, both armed from a handler through [`Cx`] and both
+//! surfacing back as ordinary **events** the machine matches in its `on State`
+//! arms — unlike `gen_server`, which routes fires to a separate handler:
+//!
+//! - [`cx.state_timeout(d)`](Cx::state_timeout) fires a `state_timeout` event
+//!   after `d` *in the current state*, and is auto-reset on any state change.
+//!   Only one is ever pending; arming again replaces it.
+//! - [`cx.timeout(name, d)`](Cx::timeout) fires a `timeout(name)` event after
+//!   `d`, **survives** state changes, and is keyed by `name` so several can be
+//!   in flight and each is independently [`cancel_timeout`](Cx::cancel_timeout)led.
+//!
+//! Both ride the same timer min-heap as `gen_server` (no separate timer
+//! mechanism): a fire lands on the loop's own system channel — above the inbox,
+//! so a timeout can't be starved by inbox traffic — and the loop turns it into
+//! the corresponding internal event and runs it through the normal `handle`
+//! dispatch.
+//!
+//! ## Postpone
+//!
+//! A `=> postpone` row defers the current event untouched, to be replayed after
+//! the next **real transition**. The deferred event — a `cast`, `call`, or
+//! `info` — moves whole onto a loop-side FIFO queue; a postponed `call` keeps
+//! its [`Reply`] handle and is answered by whichever later state handles the
+//! replay. On a transition the queue drains in order through the normal
+//! [`handle`](Machine::handle) dispatch in the new state, ahead of any further
+//! inbox or timer event; a replayed event may postpone again (it re-queues for
+//! the next transition). See the macro docs for the row surface and [`Step`]
+//! for how a postpone surfaces to the loop.
 
-use crate::channel::{channel, Receiver, Sender};
+use crate::channel::{channel, select, Receiver, Sender};
 use crate::pid::Pid;
-use crate::scheduler::spawn as spawn_actor;
+use crate::scheduler::{cancel_timer, send_after_to, spawn as spawn_actor};
+use crate::timer::TimerId;
+use std::collections::{HashMap, VecDeque};
 use std::marker::PhantomData;
+use std::sync::{Arc, Mutex};
+use std::time::Duration;
 
 // ---------------------------------------------------------------------------
 // Machine
 // ---------------------------------------------------------------------------
 
-/// A finite state machine driven by the [`statem`](crate::gen_statem) loop.
+/// A finite state machine driven by the [`statem`](mod@crate::gen_statem) loop.
 ///
 /// The implementor owns its current state tag and its persistent data. It is
 /// the **sole writer** of the state cell (the loop never touches it): both
@@ -59,28 +91,45 @@ use std::marker::PhantomData;
 /// [`handle`](Self::handle) per event.
 pub trait Machine: Send + 'static {
     /// The single payload this machine's inbox carries — the user's `cast` and
-    /// `call` enums folded together with the runtime's internal events. See the
-    /// module docs.
+    /// `call` enums folded together with the runtime's internal events
+    /// (`state_timeout`, `timeout(name)`, and an `Info` wrapper). See the module
+    /// docs.
     type Ev: Send + 'static;
 
+    /// Wrap a fired state-timeout into this machine's event. The loop calls this
+    /// when the pending state-timeout fires, then runs the result through
+    /// [`handle`](Self::handle) like any other event. The macro generates it as
+    /// `Ev::StateTimeout`.
+    fn state_timeout_ev() -> Self::Ev;
+
+    /// Wrap a fired named timeout into this machine's event, carrying the name
+    /// it was armed under. The macro generates it as `Ev::Timeout(name)`.
+    fn timeout_ev(name: &'static str) -> Self::Ev;
+
     /// Runs once inside the actor before the first event. The canonical body
     /// runs the `enter` arm for the initial state.
     fn on_start(&mut self, cx: &mut Cx<Self::Ev>);
 
-    /// React to one event. The body matches `(state, event)`, performs side
-    /// effects / replies, and ends each arm in a [`Resolution`] — typically a
-    /// state tag via `Tag.into()` (transition, or "stay" when it equals the
-    /// current tag). On a transition the body sets the state cell and runs the
-    /// new state's `enter`.
-    fn handle(&mut self, ev: Self::Ev, cx: &mut Cx<Self::Ev>);
+    /// React to one event, returning a [`Step`] the loop acts on. The body
+    /// first routes a `postpone` row (handing the event back untouched as
+    /// [`Step::Postponed`]); otherwise it matches `(state, event)`, performs
+    /// side effects / replies, and ends each arm in a [`Resolution`] — typically
+    /// a state tag via `Tag.into()` (transition, or "stay" when it equals the
+    /// current tag). On a transition the body sets the state cell, runs the new
+    /// state's `enter`, and returns [`Step::Transitioned`]; a stay or unmatched
+    /// event returns [`Step::Stayed`].
+    fn handle(&mut self, ev: Self::Ev, cx: &mut Cx<Self::Ev>) -> Step<Self::Ev>;
 }
 
 // ---------------------------------------------------------------------------
 // Resolution
 // ---------------------------------------------------------------------------
 
-/// The outcome of handling one event, before the loop/handler acts on it:
-/// dispatch reduces to `(state, event) -> Resolution<State>`.
+/// The outcome of the **consuming** dispatch — the by-value `match (state,
+/// event)` — before the apply-tail acts on it: `(state, event) ->
+/// Resolution<State>`. Postpone is *not* here: a deferred event never reaches
+/// this match (it is routed out first; see [`Step`] and the macro's two-phase
+/// `handle`), so the only outcomes are a target state or "unhandled".
 ///
 /// [`From<S>`](From) is why a bare state tag works as an arm tail and why
 /// "stay" needs no keyword — `Tag.into()` is `To(Tag)`, and the handler treats
@@ -89,10 +138,6 @@ pub enum Resolution<S> {
     /// End in state `s`. A **transition** when `s != current` (set the cell,
     /// run `enter`); a **stay** when `s == current` (no `enter`).
     To(S),
-    /// Defer the current event onto the postpone queue, to be replayed after
-    /// the next real transition. Produced by `cx.postpone()`; present
-    /// here for forward-compatibility but not yet generated.
-    Postpone,
     /// No arm matched `(state, event)`: log-and-drop via
     /// [`Cx::on_unhandled`], mirroring `gen_server`'s handling of unexpected
     /// messages.
@@ -105,31 +150,187 @@ impl<S> From<S> for Resolution<S> {
     }
 }
 
+/// What one [`handle`](Machine::handle) call did, as the loop needs to see it.
+/// Unlike [`Resolution`] (internal to the consuming match), this is the
+/// loop-visible result, because the loop must know two things the match alone
+/// doesn't surface: whether an event was **deferred** (so the loop owns it for
+/// the postpone queue) and whether a **real transition** happened (so the loop
+/// replays that queue). The three cases are mutually exclusive.
+pub enum Step<Ev> {
+    /// The event was deferred by a `postpone` row and handed back untouched.
+    /// The loop pushes it onto the postpone queue; no state change occurred.
+    Postponed(Ev),
+    /// A real transition happened (`enter` for the new state has already run).
+    /// The loop replays the postpone queue in the new state.
+    Transitioned,
+    /// Handled with no transition — a stay or an unmatched event. Nothing is
+    /// deferred and the postpone queue is left as-is.
+    Stayed,
+}
+
+// ---------------------------------------------------------------------------
+// Cx — the per-handler context
+// ---------------------------------------------------------------------------
+
+// ---------------------------------------------------------------------------
+// Sys — the loop's internal timer-fire channel
+// ---------------------------------------------------------------------------
+
+/// A timer fire landing on the loop's own system channel, selected above the
+/// inbox so a timeout cannot be starved by inbox traffic. Each fire carries the
+/// local id it was armed under so the loop can confirm it is still the live one
+/// (a fire that a reset/cancel beat onto the channel is discarded).
+enum Sys {
+    /// The state-timeout fired, carrying the local id it was armed under so the
+    /// loop can drop a stale fire (one a reset/cancel beat onto the channel).
+    StateTimeout(u64),
+    /// A named timeout fired, carrying its name and the local id it was armed
+    /// under.
+    Timeout(&'static str, u64),
+}
+
+// ---------------------------------------------------------------------------
+// Timers — shared timer bookkeeping
+// ---------------------------------------------------------------------------
+
+/// Per-machine timer bookkeeping, shared between the loop and every [`Cx`]
+/// borrow (a machine is single-threaded — handler calls and the loop never run
+/// concurrently — so this `Mutex` is always uncontended; it is `Arc<Mutex>`
+/// rather than `Rc<RefCell>` only because `Machine: Send` forces it).
+///
+/// Each arming mints a fresh **local id** carried in the fire payload and
+/// recorded here alongside the substrate id used to cancel. On fire the loop
+/// compares the payload's local id against the recorded one: a fire whose id no
+/// longer matches — a reset/cancel armed a newer one or removed the entry after
+/// this fire already escaped onto the channel — is stale and dropped. The local
+/// id is minted up front (unlike the substrate id, which only exists once armed),
+/// so it can ride the payload with no chicken-and-egg.
+struct Timers {
+    /// Monotonic minter for local ids, kept distinct from substrate ids (the
+    /// latter are what we hand to [`cancel_timer`]).
+    next_local: u64,
+    /// The currently-armed state-timeout's `(local id, substrate id)`. Cancelled
+    /// and cleared on every real state change (auto-reset), replaced on re-arm.
+    state: Option<(u64, TimerId)>,
+    /// Live named timeouts: name → `(local id, substrate id)`. Survives state
+    /// changes; an entry lives until it fires or is cancelled.
+    named: HashMap<&'static str, (u64, TimerId)>,
+}
+
+impl Timers {
+    fn new() -> Self {
+        Timers { next_local: 0, state: None, named: HashMap::new() }
+    }
+
+    fn mint(&mut self) -> u64 {
+        let id = self.next_local;
+        self.next_local = self.next_local.wrapping_add(1);
+        id
+    }
+}
+
 // ---------------------------------------------------------------------------
 // Cx — the per-handler context
 // ---------------------------------------------------------------------------
 
 /// The context handle injected into [`Machine::on_start`] and
-/// [`Machine::handle`]. Non-state outcomes (postpone, timeout arming) live here
-/// as method calls rather than keywords.
+/// [`Machine::handle`]. Non-state outcomes — timeout arming, and later
+/// postpone — live here as method calls rather than keywords. It lives only on
+/// the actor's own stack and is never sent.
 ///
-/// For now it carries only the [`on_unhandled`](Self::on_unhandled) hook;
-/// `cx.state_timeout(d)` / `cx.timeout(name, d)` and `cx.postpone()` will attach
-/// here when implemented. It lives only on the actor's own
-/// stack and is never sent.
+/// Timeouts armed here land on the loop's system channel through `sys_tx` and
+/// are tracked in the shared `reg` so reset/cancel can find the pending one.
 pub struct Cx<Ev> {
+    sys_tx: Sender<Sys>,
+    reg: Arc<Mutex<Timers>>,
     _ev: PhantomData<fn() -> Ev>,
 }
 
 impl<Ev> Cx<Ev> {
-    fn new() -> Self {
-        Cx { _ev: PhantomData }
+    fn new(sys_tx: Sender<Sys>, reg: Arc<Mutex<Timers>>) -> Self {
+        Cx { sys_tx, reg, _ev: PhantomData }
     }
 
-    /// The default for an event no arm matched: **log-and-drop**. Overridable
-    /// hook wiring is a follow-on; for now an unmatched event is
-    /// silently dropped, as `gen_server` does with unexpected messages.
+    /// Arm the **state timeout**: fire a `state_timeout` event after `after` in
+    /// the current state. Auto-reset on any state change (the loop cancels and
+    /// clears it on every real transition), so it measures quiet time *within* a
+    /// state. Only one is ever pending — arming again cancels and replaces the
+    /// previous one.
+    pub fn state_timeout(&mut self, after: Duration) {
+        let mut reg = match self.reg.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: gen_statem reg lock poisoned (core corrupt): {e}"),
+        };
+        if let Some((_, old_sub)) = reg.state.take() {
+            cancel_timer(old_sub);
+        }
+        let local = reg.mint();
+        let sub = send_after_to(after, self.sys_tx.clone(), Sys::StateTimeout(local));
+        reg.state = Some((local, sub));
+    }
+
+    /// Arm a **named generic timeout**: fire a `timeout(name)` event after
+    /// `after`. Survives state changes; several may be in flight keyed by
+    /// `name`. Arming the same `name` again cancels and replaces the pending one
+    /// for that name.
+    pub fn timeout(&mut self, name: &'static str, after: Duration) {
+        let mut reg = match self.reg.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: gen_statem reg lock poisoned (core corrupt): {e}"),
+        };
+        if let Some((_, old_sub)) = reg.named.remove(name) {
+            cancel_timer(old_sub);
+        }
+        let local = reg.mint();
+        let sub = send_after_to(after, self.sys_tx.clone(), Sys::Timeout(name, local));
+        reg.named.insert(name, (local, sub));
+    }
+
+    /// Cancel the named timeout `name` if pending. Returns `true` if the cancel
+    /// beat the fire, `false` if it had already fired / was never armed.
+    pub fn cancel_timeout(&mut self, name: &'static str) -> bool {
+        let mut reg = match self.reg.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: gen_statem reg lock poisoned (core corrupt): {e}"),
+        };
+        match reg.named.remove(name) {
+            Some((_, sub)) => cancel_timer(sub),
+            None => false,
+        }
+    }
+
+    /// Cancel the pending state-timeout if any. Returns `true` if the cancel
+    /// beat the fire. Rarely needed by hand (the loop auto-resets on
+    /// transition); exposed for a handler that wants to disarm within a state.
+    pub fn cancel_state_timeout(&mut self) -> bool {
+        let mut reg = match self.reg.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: gen_statem reg lock poisoned (core corrupt): {e}"),
+        };
+        match reg.state.take() {
+            Some((_, sub)) => cancel_timer(sub),
+            None => false,
+        }
+    }
+
+    /// The default for an event no arm matched: **log-and-drop**, as
+    /// `gen_server` does with unexpected messages.
     pub fn on_unhandled(&mut self) {}
+
+    /// Cancel and clear the pending state-timeout. Called by the macro on every
+    /// real transition (the state-timeout is auto-reset across state changes);
+    /// not part of the authoring surface. A handler re-arms in the new state's
+    /// `enter` if it wants one.
+    #[doc(hidden)]
+    pub fn __reset_state_timeout(&mut self) {
+        let mut reg = match self.reg.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: gen_statem reg lock poisoned (core corrupt): {e}"),
+        };
+        if let Some((_, sub)) = reg.state.take() {
+            cancel_timer(sub);
+        }
+    }
 }
 
 // ---------------------------------------------------------------------------
@@ -143,9 +344,8 @@ impl<Ev> Cx<Ev> {
 /// machine dies, closing the channel).
 ///
 /// Carrying the handle in the event — rather than the loop owning a reply slot
-/// — is what lets a later chunk **postpone a call**: the whole event, reply
-/// handle included, moves onto the postpone queue and is answered by a later
-/// state.
+/// — is what will let a **postponed call** work: the whole event, reply handle
+/// included, moves onto the postpone queue and is answered by a later state.
 pub struct Reply<T> {
     tx: Sender<T>,
 }
@@ -211,9 +411,7 @@ impl<M: Machine> GenStatemRef<M> {
     /// stack unwinds, closing the channel and waking the caller).
     ///
     /// `make` wraps the [`Reply`] all the way to `M::Ev` — typically
-    /// `|r| Ev::Call(MyCall::GetCount(r))`. (The deferred macro would generate a
-    /// thinner `call` that hides the `Ev::Call` wrap and takes the bare variant
-    /// constructor.)
+    /// `|r| Ev::Call(MyCall::GetCount(r))`.
     pub fn call<T, F>(&self, make: F) -> Result<T, CallError>
     where
         T: Send + 'static,
@@ -241,18 +439,84 @@ pub fn spawn<M: Machine>(machine: M) -> GenStatemRef<M> {
     GenStatemRef { tx, pid: handle.pid() }
 }
 
-/// The machine actor body: `on_start`, then one `handle` per inbox event until
-/// the inbox closes (all refs dropped → graceful shutdown). Chunk 1 parks on
-/// the inbox alone — no system arm, no timers — the analogue of `gen_server`'s
-/// plain-inbox park.
+/// The machine actor body: `on_start`, then one `handle` per event until the
+/// inbox closes (all refs dropped → graceful shutdown).
+///
+/// Two intake sources are selected each iteration with the **timer arm above
+/// the inbox**, so a timeout fire is never starved by inbox traffic: `sys_rx`
+/// carries timer fires armed through `cx`, `rx` is the user inbox. A fire is
+/// turned into the matching internal event (`state_timeout` / `timeout(name)`)
+/// and run through the same `handle` dispatch as an inbox event — the
+/// gen_statem model, where timeouts surface as ordinary events.
+///
+/// The loop owns the **postpone queue**: a `handle` that defers its event hands
+/// it back ([`Step::Postponed`]) for the queue; a `handle` that transitions
+/// ([`Step::Transitioned`]) triggers a [`replay`] of the queue in the new
+/// state, ahead of the next intake.
 fn statem_loop<M: Machine>(rx: Receiver<M::Ev>, mut machine: M) {
-    let mut cx = Cx::new();
+    let (sys_tx, sys_rx) = channel::<Sys>();
+    let reg = Arc::new(Mutex::new(Timers::new()));
+    // The loop owns `cx` (and through it a `sys_tx` clone) for its whole life,
+    // so the sys arm never closes from under us — no auto-close dance needed.
+    let mut cx = Cx::new(sys_tx, reg.clone());
+    // Events deferred by `postpone` rows, replayed FIFO on the next transition.
+    let mut postpone: VecDeque<M::Ev> = VecDeque::new();
     machine.on_start(&mut cx);
     loop {
-        match rx.recv() {
-            Ok(ev) => machine.handle(ev, &mut cx),
-            // All StatemRefs dropped → inbox closed → shutdown.
-            Err(_) => break,
+        // Timer arm first: a ready fire is taken in preference to the inbox.
+        let i = select(&[&sys_rx, &rx]);
+        if i == 0 {
+            match sys_rx.try_recv() {
+                Ok(Some(fire)) => {
+                    // Confirm the fire is still the live one before dispatching:
+                    // a reset/cancel may have replaced/removed it after it
+                    // escaped onto the channel. A stale fire is dropped.
+                    let ev = match fire {
+                        Sys::StateTimeout(local) => {
+                            let mut t = match reg.lock() {
+                                Ok(g) => g,
+                                Err(e) => panic!("smarm: gen_statem reg lock poisoned (core corrupt): {e}"),
+                            };
+                            match t.state {
+                                Some((live, _)) if live == local => {
+                                    t.state = None; // retire: it has now fired
+                                    Some(M::state_timeout_ev())
+                                }
+                                _ => None,
+                            }
+                        }
+                        Sys::Timeout(name, local) => {
+                            let mut t = match reg.lock() {
+                                Ok(g) => g,
+                                Err(e) => panic!("smarm: gen_statem reg lock poisoned (core corrupt): {e}"),
+                            };
+                            match t.named.get(name) {
+                                Some(&(live, _)) if live == local => {
+                                    t.named.remove(name); // retire on fire
+                                    Some(M::timeout_ev(name))
+                                }
+                                _ => None,
+                            }
+                        }
+                    };
+                    if let Some(ev) = ev {
+                        dispatch(&mut machine, &mut cx, &mut postpone, ev);
+                    }
+                }
+                // Single-receiver: nothing can drain the arm between select's
+                // ready and our try_recv.
+                Ok(None) => debug_assert!(false, "ready system arm was empty"),
+                // The loop holds a sys_tx for its whole life, so this is
+                // unreachable; fall through defensively.
+                Err(_) => {}
+            }
+        } else {
+            match rx.try_recv() {
+                Ok(Some(ev)) => dispatch(&mut machine, &mut cx, &mut postpone, ev),
+                Ok(None) => debug_assert!(false, "ready inbox was empty"),
+                // All GenStatemRefs dropped → inbox closed → shutdown.
+                Err(_) => break,
+            }
         }
         // Observation point so a machine fed a hot inbox stays preemptible and
         // cancellable.
@@ -260,15 +524,60 @@ fn statem_loop<M: Machine>(rx: Receiver<M::Ev>, mut machine: M) {
     }
 }
 
+/// Run one event through `handle` and act on its [`Step`]: stash a deferred
+/// event on the postpone queue, or — on a real transition — [`replay`] the
+/// queue in the new state. A stay/unmatched event needs nothing further.
+fn dispatch<M: Machine>(
+    machine: &mut M,
+    cx: &mut Cx<M::Ev>,
+    postpone: &mut VecDeque<M::Ev>,
+    ev: M::Ev,
+) {
+    match machine.handle(ev, cx) {
+        Step::Postponed(ev) => postpone.push_back(ev),
+        Step::Stayed => {}
+        Step::Transitioned => replay(machine, cx, postpone),
+    }
+}
+
+/// Replay deferred events after a real transition: each goes back through
+/// `handle` in FIFO order, in the now-current state. An event that postpones
+/// again re-queues (to wait for the *next* transition); one that transitions
+/// re-arms the replay, so a later state can in turn drain what is still pending.
+/// Subsequent events in a batch already see the post-transition state, since
+/// `handle` reads the live state cell — the outer loop only re-runs to give
+/// re-queued events another pass once a transition has occurred within a batch.
+fn replay<M: Machine>(machine: &mut M, cx: &mut Cx<M::Ev>, postpone: &mut VecDeque<M::Ev>) {
+    loop {
+        if postpone.is_empty() {
+            return;
+        }
+        // Take the current backlog; anything deferred during this pass lands in
+        // the now-empty queue and is only retried if this pass also transitioned.
+        let batch = std::mem::take(postpone);
+        let mut transitioned = false;
+        for ev in batch {
+            match machine.handle(ev, cx) {
+                Step::Postponed(ev) => postpone.push_back(ev),
+                Step::Stayed => {}
+                Step::Transitioned => transitioned = true,
+            }
+        }
+        if !transitioned {
+            return;
+        }
+    }
+}
+
 // ---------------------------------------------------------------------------
-// gen_statem! — the authoring macro (fused total-match variant)
+// gen_statem! — the authoring macro (total-match dispatch)
 // ---------------------------------------------------------------------------
 
 /// Assemble a complete [`Machine`] from hand-written types, a glanceable
 /// transition table, and free handler functions.
 ///
-/// This is the **fused** authoring surface (see `examples/statem_fused.rs` for
-/// the same machine written out by hand). You keep ownership of every type that
+/// This is the authoring surface (see `examples/gen_statem_expanded.rs` for the
+/// same machine written out by hand). You keep ownership of every type that
 /// carries meaning — the state enum, the data struct, the `cast`/`call` enums,
 /// and any per-row successor enums — and the macro emits only the mechanical
 /// scaffolding: the unified event enum, the machine struct and its private
@@ -308,12 +617,12 @@ fn statem_loop<M: Machine>(rx: Receiver<M::Ev>, mut machine: M) {
 ///    machine lives in the same crate as this macro, and is **silently dropped
 ///    when you call `gen_statem!` from a downstream crate** — neither a crate
 ///    `#![deny]` nor `#![forbid]` overrides the suppression. This is the one
-///    guarantee a `macro_rules!` cannot carry across the crate boundary; the
-///    RFC's proc-macro could (it would stamp the arms with call-site spans).
+///    guarantee a `macro_rules!` cannot carry across the crate boundary; a
+///    proc-macro could (it would stamp the arms with call-site spans).
 ///    Guard against it in review, or with an in-crate test of the machine.
 ///
 /// There is deliberately **no separate `transitions { … }` adjacency block**:
-/// in this variant the `match` *is* the table and the successor enums *are* the
+/// the `match` *is* the table and the successor enums *are* the
 /// per-state target sets, so a second listing would be redundant and
 /// un-cross-checkable without a proc-macro. The graph is read off the `on`
 /// blocks and the successor enums at the top of the file.
@@ -323,14 +632,16 @@ fn statem_loop<M: Machine>(rx: Receiver<M::Ev>, mut machine: M) {
 /// ```ignore
 /// // ── your types (the macro never generates or inspects these) ───────────
 /// #[derive(Clone, Copy, PartialEq, Eq, Debug)]
-/// enum Switch { Off, On }
-/// struct Counts { flips: u32, enters: u32 }
-/// enum SwitchCast { Flip }
-/// enum SwitchCall { GetCount(Reply<u32>) }
+/// enum Door { Open, Closed, Locked }
+/// struct Data { enters: u32 }
+/// enum DoorCast { Push, Pull, Lock, Unlock(u32) }
+/// enum DoorCall { GetState(Reply<Door>) }
 ///
 /// gen_statem! {
-///     machine: SwitchSm { state: Switch, data: Counts };
-///     event:   Ev { cast: SwitchCast, call: SwitchCall };
+///     machine: DoorSm { state: Door, data: Data };
+///     // The event clause folds three user enums together. `info` is for
+///     // out-of-band messages; use `()` if you have none.
+///     event:   Ev { cast: DoorCast, call: DoorCall, info: () };
 ///
 ///     // Name the bindings your handler bodies use. A declarative macro can't
 ///     // hand you its own `self`/`cx` (hygiene), so you choose the identifiers
@@ -339,26 +650,51 @@ fn statem_loop<M: Machine>(rx: Receiver<M::Ev>, mut machine: M) {
 ///     context(data, prev, cx);
 ///
 ///     // `enter` runs on entry to a state; side effects only, returns ().
-///     // Match the state tag (or `_`); the arm body is statements.
+///     // Match the state tag (or `_`); the arm body is statements. Arm any
+///     // state-timeout here (it is auto-reset on the way into a new state).
 ///     enter {
+///         Door::Open => {
+///             data.enters += 1;
+///             cx.state_timeout(std::time::Duration::from_secs(30)); // auto-close
+///         }
 ///         _ => data.enters += 1,
 ///     }
 ///
 ///     // The transition table. Group rows by current state with `on <pat>`.
-///     // A row is:  cast|call  <event-pattern>  [if <guard>]  =>  <tail> ,
+///     // A row is:  <kind> <event-pattern> [if <guard>]  =>  <tail> ,
+///     // where <kind> is one of `cast`, `call`, `info`, `state_timeout`
+///     // (no pattern — it is a unit event), or `timeout <name-pattern>`,
 ///     // and the tail is one of:
-///     //   * a state tag            `Switch::On`        (transition, or "stay"
-///     //                                                  if it equals current)
-///     //   * a block ending in one  `{ data.flips += 1; Switch::On }`
-///     //   * a successor-enum value `unlock(key)`       (branching row)
-///     //   * the keyword            `unhandled`         (explicit refusal)
-///     on Switch::Off => {
-///         cast SwitchCast::Flip            => { data.flips += 1; Switch::On },
-///         call SwitchCall::GetCount(r)     => { r.reply(data.flips); prev },
+///     //   * a state tag            `Door::Closed`     (transition, or "stay"
+///     //                                                 if it equals current)
+///     //   * a block ending in one  `{ data.enters += 1; Door::Closed }`
+///     //   * a successor-enum value `on_unlock(key)`   (branching row)
+///     //   * the keyword            `unhandled`        (explicit refusal)
+///     //   * the keyword            `postpone`         (defer until next
+///     //                                                transition; cast/call/
+///     //                                                info only)
+///     on Door::Open => {
+///         cast DoorCast::Push                       => Door::Closed,
+///         // An armed state-timeout surfaces as an ordinary event:
+///         state_timeout                             => Door::Closed,
+///         cast DoorCast::Pull | DoorCast::Lock | DoorCast::Unlock(_) => unhandled,
 ///     }
-///     on Switch::On => {
-///         cast SwitchCast::Flip            => Switch::Off,
-///         call SwitchCall::GetCount(r)     => { r.reply(data.flips); prev },
+///     on Door::Closed => {
+///         cast DoorCast::Pull                       => Door::Open,
+///         cast DoorCast::Lock                       => Door::Locked,
+///         cast DoorCast::Push | DoorCast::Unlock(_) => unhandled,
+///         // No state-timeout armed here, so refuse it.
+///         state_timeout                             => unhandled,
+///     }
+///     on Door::Locked => {
+///         cast DoorCast::Unlock(key)                => on_unlock(key), // -> successor enum
+///         cast DoorCast::Push | DoorCast::Pull | DoorCast::Lock => unhandled,
+///         state_timeout                             => unhandled,
+///     }
+///
+///     // state-independent queries (reply, then stay via `prev`)
+///     on _ => {
+///         call DoorCall::GetState(r) => { r.reply(prev); prev },
 ///     }
 /// }
 /// ```
@@ -368,30 +704,53 @@ fn statem_loop<M: Machine>(rx: Receiver<M::Ev>, mut machine: M) {
 /// * **Every row ends in a comma** (block-bodied ones too) and every `on` block
 ///   is `on <state-pat> => { … }`. These two are macro-grammar requirements, not
 ///   style: a declarative matcher can't otherwise tell where a row's tail ends.
-/// * **Qualify event patterns** (`SwitchCast::Flip`) and **state tags**
-///   (`Switch::On`). A declarative macro can't prepend the enum name inside an
-///   opaque pattern fragment, so the `cast`/`call` keyword only selects the
-///   event wrapper — it does not qualify for you. The keyword also reads as a
-///   sync/async marker at a glance.
+/// * **Qualify event patterns** (`DoorCast::Push`) and **state tags**
+///   (`Door::Closed`). A declarative macro can't prepend the enum name inside an
+///   opaque pattern fragment, so the row keyword only selects the event wrapper
+///   — it does not qualify for you. `cast`/`call` also read as a sync/async
+///   marker at a glance.
+/// * **Timeouts surface as events.** `state_timeout` (a unit event) and
+///   `timeout <name>` (matching the `&'static str` a generic timeout was armed
+///   under) are matched in `on` rows just like casts and calls — arm them via
+///   `cx`, handle the fire here. Because a `timeout` name is an `&str`, a row
+///   that matches specific names needs a `timeout _ => …` fallback to stay
+///   exhaustive.
+/// * **`info` defaults to a silent drop.** An out-of-band `info` you do not
+///   match anywhere is dropped (the `gen_server` default), so a machine that
+///   ignores info writes no `info` rows at all. State-timeouts and named
+///   timeouts have **no** such default: a state that can see one must handle it
+///   (or `unhandled` it) or the match is non-exhaustive.
 /// * **Stay** = return the current tag. The `prev` you named in `context` is
 ///   bound to the pre-handler state for exactly this — handy in any-state
 ///   (`on _`) rows where there is no single literal tag to write.
 /// * **`data` and `cx`** (the names you chose) are in scope in every body:
-///   mutate `data`, reply through a `Reply` bound in the pattern, and (chunks
-///   2–3) arm timeouts or postpone via `cx`. You never write `self`.
+///   mutate `data`, reply through a `Reply` bound in the pattern, and arm
+///   timeouts via `cx`. You never write `self`.
 /// * **Guards** are plain match guards. A guarded arm does not count toward
 ///   exhaustiveness, so pair it with an unguarded fallback or you'll (correctly)
 ///   trip `E0004`.
 /// * **Branching rows** return a successor enum that `impl`s `From<_>` for the
 ///   state type; the macro supplies the outer `.into()`.
+/// * **`postpone`** defers the current event untouched, to be replayed after the
+///   next *real transition* (a stay does not trigger replay). It is available
+///   for `cast`, `call`, and `info` rows — not the timeout events. The deferred
+///   event keeps any `Reply` it carries, so a postponed `call` is answered by
+///   whichever later state handles the replay. The body runs *no* code (the
+///   event is untouched), so a `postpone` row is just `cast Foo(_) => postpone,`;
+///   prefer a non-binding pattern, and if you guard it, the guard must not depend
+///   on the event's payload (it is evaluated in a borrow pre-pass). On a
+///   transition the queue drains FIFO, ahead of further inbox/timer events; a
+///   replayed event may postpone again (it re-queues for the next transition).
 ///
 /// # What it emits
 ///
-/// `enum $Ev { Cast($Cast), Call($Call) }`, `struct $Sm { state, data }`,
-/// `$Sm::start(init, data) -> GenStatemRef<$Sm>`, the `Machine` impl (`on_start`
-/// running the initial `enter`; `handle` = the dispatch match + the
-/// stay/transition/unhandled apply-tail, the cell's sole writer), and the
-/// `enter` dispatch. Chunk 1: real time, no timers, no postpone.
+/// The unified `enum $Ev` (the `Cast`/`Call`/`Info` wrappers plus the internal
+/// `StateTimeout` / `Timeout` events), `struct $Sm { state, data }`,
+/// `$Sm::start(init, data) -> GenStatemRef<$Sm>`, and the `Machine` impl:
+/// `on_start` runs the initial `enter`; `handle` is the dispatch match plus the
+/// stay/transition/unhandled apply-tail (the cell's sole writer, which also
+/// auto-resets the state-timeout on every real transition); and the `enter`
+/// dispatch.
 ///
 /// # Limitation
 ///
@@ -403,16 +762,23 @@ macro_rules! gen_statem {
     // ===== public entry =====================================================
     (
         machine: $sm:ident { state: $State:ty, data: $Data:ty } ;
-        event:   $Ev:ident { cast: $Cast:ty, call: $Call:ty } ;
+        event:   $Ev:ident { cast: $Cast:ty, call: $Call:ty, info: $Info:ty } ;
         context ( $data:ident , $cur:ident , $cx:ident ) ;
         enter { $( $est:pat => $ebody:expr ),+ $(,)? }
         $( on $st:pat => { $($rows:tt)* } )+
     ) => {
-        /// Unified inbox payload: the user's `cast`/`call` enums folded together
-        /// (chunks 2–3 add the runtime's internal timeout variants here).
+        /// Unified inbox payload: the user's `cast`/`call`/`info` enums folded
+        /// together with the runtime's internal timeout events.
         enum $Ev {
             Cast($Cast),
             Call($Call),
+            /// Out-of-band message, matched in `info` rows. An unmatched info is
+            /// silently dropped (the `gen_server` default).
+            Info($Info),
+            /// The state-timeout fired (matched in `state_timeout` rows).
+            StateTimeout,
+            /// A named timeout fired (matched in `timeout <pat>` rows).
+            Timeout(&'static str),
         }
 
         struct $sm {
@@ -438,6 +804,14 @@ macro_rules! gen_statem {
         impl $crate::gen_statem::Machine for $sm {
             type Ev = $Ev;
 
+            fn state_timeout_ev() -> $Ev {
+                $Ev::StateTimeout
+            }
+
+            fn timeout_ev(name: &'static str) -> $Ev {
+                $Ev::Timeout(name)
+            }
+
             fn on_start(&mut self, $cx: &mut $crate::gen_statem::Cx<$Ev>) {
                 let s = self.state;
                 self.enter(s, $cx);
@@ -446,79 +820,205 @@ macro_rules! gen_statem {
             #[allow(unused_variables)]
             #[deny(unreachable_patterns)] // conflicting rows must fail even though
                                           // this match is external-macro-expanded
-            fn handle(&mut self, ev: $Ev, $cx: &mut $crate::gen_statem::Cx<$Ev>) {
+            fn handle(&mut self, ev: $Ev, $cx: &mut $crate::gen_statem::Cx<$Ev>)
+                -> $crate::gen_statem::Step<$Ev>
+            {
                 // Caller-named bindings (shared call-site hygiene, so row bodies
                 // can see them): `$cur` = current state tag, `$data` = &mut Data.
                 let $cur = self.state;
                 let $data = &mut self.data;
+                // @arms emits a block: a postpone pre-pass that `return`s
+                // `Step::Postponed(ev)` for a deferred event (handing it back
+                // untouched), then the consuming `match (state, event)` whose
+                // value is this `Resolution`.
                 let next: $crate::gen_statem::Resolution<$State> =
-                    $crate::gen_statem!(@arms ($Ev) ($cur, ev) [ ]
+                    $crate::gen_statem!(@arms ($Ev) ($cur, ev) [ ] [ ]
                         $( on $st => { $($rows)* } )+);
                 match next {
-                    $crate::gen_statem::Resolution::To(s) if s == $cur => {}
+                    $crate::gen_statem::Resolution::To(s) if s == $cur => {
+                        $crate::gen_statem::Step::Stayed
+                    }
                     $crate::gen_statem::Resolution::To(s) => {
                         self.state = s; // <- sole writer of the state cell
+                        // A real transition auto-resets the state-timeout: the
+                        // new state re-arms in its `enter` if it wants one.
+                        $cx.__reset_state_timeout();
                         self.enter(s, $cx);
+                        $crate::gen_statem::Step::Transitioned
                     }
-                    $crate::gen_statem::Resolution::Postpone => {
-                        unreachable!("postpone is not generated yet")
+                    $crate::gen_statem::Resolution::Unhandled => {
+                        $cx.on_unhandled();
+                        $crate::gen_statem::Step::Stayed
                     }
-                    $crate::gen_statem::Resolution::Unhandled => $cx.on_unhandled(),
                 }
             }
         }
     };
 
-    // ===== @arms: build the dispatch match ==================================
-    // No more on-blocks: emit the (total, catch-all-free) match.
-    (@arms ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ]) => {
-        match ($ss, $se) { $($arms)* }
+    // ===== @arms / @rows: build the two-phase dispatch ======================
+    // Two accumulators are threaded: `[ $($arms)* ]` is the phase-2 consuming
+    // match (by value); `[ $($post)* ]` is the phase-1 postpone router (by ref).
+    // A normal row feeds only phase-2; a `postpone` row feeds both — a `=> true`
+    // router and a `=> unreachable!` phase-2 filler that keeps the consuming
+    // match total.
+    //
+    // Terminal (no on-blocks left): emit the block the `handle` body assigns to
+    // `next`. Phase 1 routes a deferred event back out as `Step::Postponed`;
+    // phase 2 is the catch-all-free consuming match (the one macro-injected arm
+    // is the `Info` silent-drop — last and broadest, so per-state `info` rows
+    // stay reachable; cast/call/timeouts get no fallback, so a forgotten pair is
+    // still E0004).
+    (@arms ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ]) => {
+        {
+            // Phase 1 — postpone routing (borrow-only). A guard on a postpone
+            // row runs here, against by-ref bindings, so it must not depend on
+            // the event's payload.
+            let __defer = match ($ss, &$se) {
+                $($post)*
+                _ => false,
+            };
+            if __defer {
+                return $crate::gen_statem::Step::Postponed($se);
+            }
+            // Phase 2 — the consuming dispatch. Each postpone pair reappears here
+            // as `unreachable!` so the match stays total; phase 1 already
+            // returned for it.
+            match ($ss, $se) {
+                $($arms)*
+                (_, $Ev::Info(_)) => $crate::gen_statem::Resolution::Unhandled,
+            }
+        }
     };
     // Open an on-block: remember its state pat, drain its rows, then continue.
-    (@arms ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ]
+    (@arms ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ]
         on $st:pat => { $($rows:tt)* } $($more:tt)*
     ) => {
-        $crate::gen_statem!(@rows ($Ev) ($ss, $se) [ $($arms)* ] ($st)
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se) [ $($arms)* ] [ $($post)* ] ($st)
             { $($rows)* } { $($more)* })
     };
 
-    // ===== @rows: drain one on-block's rows, threading the global acc ========
+    // ===== @rows: drain one on-block's rows, threading both accs =============
     // cast, explicit refusal
-    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] ($st:pat)
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
         { cast $ev:pat $(if $g:expr)? => unhandled , $($rows:tt)* } { $($more:tt)* }
     ) => {
         $crate::gen_statem!(@rows ($Ev) ($ss, $se)
             [ $($arms)* ($st, $Ev::Cast($ev)) $(if $g)? => $crate::gen_statem::Resolution::Unhandled, ]
+            [ $($post)* ]
+            ($st) { $($rows)* } { $($more)* })
+    };
+    // cast, postpone (defer the event; the replay in a later state handles it)
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
+        { cast $ev:pat $(if $g:expr)? => postpone , $($rows:tt)* } { $($more:tt)* }
+    ) => {
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se)
+            [ $($arms)* ($st, $Ev::Cast($ev)) $(if $g)? => unreachable!("postponed event is replayed, not dispatched here"), ]
+            [ $($post)* ($st, $Ev::Cast($ev)) $(if $g)? => true, ]
             ($st) { $($rows)* } { $($more)* })
     };
     // cast, transition / stay / branch
-    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] ($st:pat)
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
         { cast $ev:pat $(if $g:expr)? => $tail:expr , $($rows:tt)* } { $($more:tt)* }
     ) => {
         $crate::gen_statem!(@rows ($Ev) ($ss, $se)
             [ $($arms)* ($st, $Ev::Cast($ev)) $(if $g)? => $crate::gen_statem::Resolution::To($tail.into()), ]
+            [ $($post)* ]
             ($st) { $($rows)* } { $($more)* })
     };
     // call, explicit refusal
-    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] ($st:pat)
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
         { call $ev:pat $(if $g:expr)? => unhandled , $($rows:tt)* } { $($more:tt)* }
     ) => {
         $crate::gen_statem!(@rows ($Ev) ($ss, $se)
             [ $($arms)* ($st, $Ev::Call($ev)) $(if $g)? => $crate::gen_statem::Resolution::Unhandled, ]
+            [ $($post)* ]
+            ($st) { $($rows)* } { $($more)* })
+    };
+    // call, postpone (the Reply rides inside the event onto the queue)
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
+        { call $ev:pat $(if $g:expr)? => postpone , $($rows:tt)* } { $($more:tt)* }
+    ) => {
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se)
+            [ $($arms)* ($st, $Ev::Call($ev)) $(if $g)? => unreachable!("postponed event is replayed, not dispatched here"), ]
+            [ $($post)* ($st, $Ev::Call($ev)) $(if $g)? => true, ]
             ($st) { $($rows)* } { $($more)* })
     };
     // call, transition / stay / branch
-    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] ($st:pat)
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
         { call $ev:pat $(if $g:expr)? => $tail:expr , $($rows:tt)* } { $($more:tt)* }
     ) => {
         $crate::gen_statem!(@rows ($Ev) ($ss, $se)
             [ $($arms)* ($st, $Ev::Call($ev)) $(if $g)? => $crate::gen_statem::Resolution::To($tail.into()), ]
+            [ $($post)* ]
+            ($st) { $($rows)* } { $($more)* })
+    };
+    // info, explicit refusal
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
+        { info $ev:pat $(if $g:expr)? => unhandled , $($rows:tt)* } { $($more:tt)* }
+    ) => {
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se)
+            [ $($arms)* ($st, $Ev::Info($ev)) $(if $g)? => $crate::gen_statem::Resolution::Unhandled, ]
+            [ $($post)* ]
+            ($st) { $($rows)* } { $($more)* })
+    };
+    // info, postpone
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
+        { info $ev:pat $(if $g:expr)? => postpone , $($rows:tt)* } { $($more:tt)* }
+    ) => {
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se)
+            [ $($arms)* ($st, $Ev::Info($ev)) $(if $g)? => unreachable!("postponed event is replayed, not dispatched here"), ]
+            [ $($post)* ($st, $Ev::Info($ev)) $(if $g)? => true, ]
+            ($st) { $($rows)* } { $($more)* })
+    };
+    // info, transition / stay / branch
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
+        { info $ev:pat $(if $g:expr)? => $tail:expr , $($rows:tt)* } { $($more:tt)* }
+    ) => {
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se)
+            [ $($arms)* ($st, $Ev::Info($ev)) $(if $g)? => $crate::gen_statem::Resolution::To($tail.into()), ]
+            [ $($post)* ]
+            ($st) { $($rows)* } { $($more)* })
+    };
+    // state_timeout, explicit refusal (unit event — no pattern; not postponable)
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
+        { state_timeout $(if $g:expr)? => unhandled , $($rows:tt)* } { $($more:tt)* }
+    ) => {
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se)
+            [ $($arms)* ($st, $Ev::StateTimeout) $(if $g)? => $crate::gen_statem::Resolution::Unhandled, ]
+            [ $($post)* ]
+            ($st) { $($rows)* } { $($more)* })
+    };
+    // state_timeout, transition / stay / branch
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
+        { state_timeout $(if $g:expr)? => $tail:expr , $($rows:tt)* } { $($more:tt)* }
+    ) => {
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se)
+            [ $($arms)* ($st, $Ev::StateTimeout) $(if $g)? => $crate::gen_statem::Resolution::To($tail.into()), ]
+            [ $($post)* ]
+            ($st) { $($rows)* } { $($more)* })
+    };
+    // timeout, explicit refusal (pattern matches the name; not postponable)
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
+        { timeout $ev:pat $(if $g:expr)? => unhandled , $($rows:tt)* } { $($more:tt)* }
+    ) => {
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se)
+            [ $($arms)* ($st, $Ev::Timeout($ev)) $(if $g)? => $crate::gen_statem::Resolution::Unhandled, ]
+            [ $($post)* ]
+            ($st) { $($rows)* } { $($more)* })
+    };
+    // timeout, transition / stay / branch
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
+        { timeout $ev:pat $(if $g:expr)? => $tail:expr , $($rows:tt)* } { $($more:tt)* }
+    ) => {
+        $crate::gen_statem!(@rows ($Ev) ($ss, $se)
+            [ $($arms)* ($st, $Ev::Timeout($ev)) $(if $g)? => $crate::gen_statem::Resolution::To($tail.into()), ]
+            [ $($post)* ]
             ($st) { $($rows)* } { $($more)* })
     };
     // this block is drained: hand the remaining on-blocks back to @arms
-    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] ($st:pat)
+    (@rows ($Ev:ident) ($ss:expr, $se:expr) [ $($arms:tt)* ] [ $($post:tt)* ] ($st:pat)
         { } { $($more:tt)* }
     ) => {
-        $crate::gen_statem!(@arms ($Ev) ($ss, $se) [ $($arms)* ] $($more)*)
+        $crate::gen_statem!(@arms ($Ev) ($ss, $se) [ $($arms)* ] [ $($post)* ] $($more)*)
     };
 }

src/io.rs

@@ -240,15 +240,18 @@ impl IoThread {
         self.outstanding += 1;
         // Send can only fail if the pool has hung up, which only happens
         // on shutdown. submit during shutdown is a bug.
-        self.tx
-            .send(Request { pid, epoch, work })
-            .expect("io pool hung up unexpectedly");
+        if self.tx.send(Request { pid, epoch, work }).is_err() {
+            panic!("smarm: io pool hung up unexpectedly (submit during shutdown)");
+        }
     }
 
     /// Drain every available completion. Caller (the scheduler) routes the
     /// results and updates `outstanding` / `waiters` accordingly.
     pub fn drain_completions(&mut self) -> Vec<Completion> {
-        let mut q = self.completions.lock().unwrap();
+        let mut q = match self.completions.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: io completions lock poisoned (core corrupt): {e}"),
+        };
         let mut out = Vec::with_capacity(q.len());
         while let Some(c) = q.pop_front() {
             out.push(c);
@@ -389,10 +392,10 @@ fn pool_loop(
             Ok(r) => r,
             Err(payload) => Err(payload),
         };
-        completions
-            .lock()
-            .unwrap()
-            .push_back(Completion::Blocking { pid, epoch, result });
+        match completions.lock() {
+            Ok(mut g) => g.push_back(Completion::Blocking { pid, epoch, result }),
+            Err(e) => panic!("smarm: io completions lock poisoned (core corrupt): {e}"),
+        }
         wake_scheduler(wake_write);
     }
 }
@@ -435,7 +438,10 @@ fn epoll_loop(
         let mut shutdown_requested = false;
         let mut pushed_any = false;
         {
-            let mut q = completions.lock().unwrap();
+            let mut q = match completions.lock() {
+                Ok(g) => g,
+                Err(e) => panic!("smarm: io completions lock poisoned (core corrupt): {e}"),
+            };
             for ev in events.iter().take(n as usize) {
                 if ev.u64 == SHUTDOWN_EPOLL_TOKEN {
                     shutdown_requested = true;

src/link.rs

@@ -135,7 +135,10 @@ pub fn link<A>(target: Pid<A>) {
 
     if registered_on_target {
         with_runtime(|inner| {
-            let slot = inner.slot_at(me).expect("link: own slot vanished");
+            let slot = match inner.slot_at(me) {
+                Some(s) => s,
+                None => panic!("smarm: link own slot vanished (core corrupt)"),
+            };
             let mut cold = slot.cold.lock();
             if !cold.links.contains(&target) {
                 cold.links.push(target);

src/mutex.rs

@@ -64,7 +64,10 @@ impl MutexCore {
 impl TimerTarget for MutexCore {
     fn on_timeout(&self, pid: Pid, epoch: u32) {
         let unpark = {
-            let mut st = self.state.lock().unwrap();
+            let mut st = match self.state.lock() {
+                Ok(g) => g,
+                Err(e) => panic!("smarm: mutex state lock poisoned (core corrupt): {e}"),
+            };
             // Remove from waiters only if still there with matching epoch.
             // If the lock was already granted (holder == Some(pid)), the
             // timer fired after the grant — treat as no-op; the actor
@@ -72,12 +75,12 @@ impl TimerTarget for MutexCore {
             if st.holder == Some(pid) {
                 return;
             }
-            let pos = st.waiters.iter().position(|w| w.pid == pid && w.epoch == epoch);
-            if pos.is_some() {
-                st.waiters.remove(pos.unwrap());
-                true
-            } else {
-                false
+            match st.waiters.iter().position(|w| w.pid == pid && w.epoch == epoch) {
+                Some(pos) => {
+                    st.waiters.remove(pos);
+                    true
+                }
+                None => false,
             }
         };
         if unpark {
@@ -105,11 +108,17 @@ impl<T> Mutex<T> {
     }
 
     pub fn set_default_timeout(&self, timeout: Duration) {
-        self.core.state.lock().unwrap().default_timeout = timeout;
+        match self.core.state.lock() {
+            Ok(mut st) => st.default_timeout = timeout,
+            Err(e) => panic!("smarm: mutex state lock poisoned (core corrupt): {e}"),
+        }
     }
 
     pub fn lock(&self) -> Result<MutexGuard<'_, T>, LockTimeout> {
-        let timeout = self.core.state.lock().unwrap().default_timeout;
+        let timeout = match self.core.state.lock() {
+            Ok(st) => st.default_timeout,
+            Err(e) => panic!("smarm: mutex state lock poisoned (core corrupt): {e}"),
+        };
         self.lock_timeout(timeout)
     }
 
@@ -122,12 +131,21 @@ impl<T> Mutex<T> {
 
         // Fast path: nobody holds it.
         {
-            let mut st = self.core.state.lock().unwrap();
+            let mut st = match self.core.state.lock() {
+                Ok(g) => g,
+                Err(e) => panic!("smarm: mutex state lock poisoned (core corrupt): {e}"),
+            };
             if st.holder.is_none() {
                 st.holder = Some(me);
                 drop(st);
-                let value = self.value.lock().unwrap().take()
-                    .expect("Mutex: value missing on free fast path");
+                let taken = match self.value.lock() {
+                    Ok(mut g) => g.take(),
+                    Err(e) => panic!("smarm: mutex value lock poisoned (core corrupt): {e}"),
+                };
+                let value = match taken {
+                    Some(v) => v,
+                    None => panic!("smarm: Mutex value missing on free fast path (core corrupt)"),
+                };
                 return Ok(MutexGuard { mutex: self, value: Some(value) });
             }
         }
@@ -135,7 +153,10 @@ impl<T> Mutex<T> {
         // Slow path: register as a waiter, set timeout, park.
         let _np = scheduler::NoPreempt::enter();
         let epoch = {
-            let mut st = self.core.state.lock().unwrap();
+            let mut st = match self.core.state.lock() {
+                Ok(g) => g,
+                Err(e) => panic!("smarm: mutex state lock poisoned (core corrupt): {e}"),
+            };
             // begin_wait is lock-free — legal under the state lock; this
             // makes the epoch atomic with the registration's visibility to
             // grants and timeouts.
@@ -153,10 +174,19 @@ impl<T> Mutex<T> {
         // wait (both epoch-stamped; a stop wake unwinds out of
         // park_current). The one-shot interpretation below is therefore
         // exhaustive. Are we the holder?
-        let is_holder = self.core.state.lock().unwrap().holder == Some(me);
+        let is_holder = match self.core.state.lock() {
+            Ok(st) => st.holder == Some(me),
+            Err(e) => panic!("smarm: mutex state lock poisoned (core corrupt): {e}"),
+        };
         if is_holder {
-            let value = self.value.lock().unwrap().take()
-                .expect("Mutex: value missing after grant");
+            let taken = match self.value.lock() {
+                Ok(mut g) => g.take(),
+                Err(e) => panic!("smarm: mutex value lock poisoned (core corrupt): {e}"),
+            };
+            let value = match taken {
+                Some(v) => v,
+                None => panic!("smarm: Mutex value missing after grant (core corrupt)"),
+            };
             Ok(MutexGuard { mutex: self, value: Some(value) })
         } else {
             Err(LockTimeout)
@@ -165,14 +195,23 @@ impl<T> Mutex<T> {
 
     pub fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
         let me = crate::actor::current_pid()?;
-        let mut st = self.core.state.lock().unwrap();
+        let mut st = match self.core.state.lock() {
+            Ok(g) => g,
+            Err(e) => panic!("smarm: mutex state lock poisoned (core corrupt): {e}"),
+        };
         if st.holder.is_some() {
             return None;
         }
         st.holder = Some(me);
         drop(st);
-        let value = self.value.lock().unwrap().take()
-            .expect("Mutex: value missing on try_lock free path");
+        let taken = match self.value.lock() {
+            Ok(mut g) => g.take(),
+            Err(e) => panic!("smarm: mutex value lock poisoned (core corrupt): {e}"),
+        };
+        let value = match taken {
+            Some(v) => v,
+            None => panic!("smarm: Mutex value missing on try_lock free path (core corrupt)"),
+        };
         Some(MutexGuard { mutex: self, value: Some(value) })
     }
 
@@ -183,7 +222,10 @@ impl<T> Mutex<T> {
         // tracking and just grab the value mutex directly.  This is safe because
         // outside the runtime there are no green threads competing.
         let value = loop {
-            let v = self.value.lock().unwrap().take();
+            let v = match self.value.lock() {
+                Ok(mut g) => g.take(),
+                Err(e) => panic!("smarm: mutex value lock poisoned (core corrupt): {e}"),
+            };
             if let Some(v) = v { break v; }
             std::thread::yield_now();
         };
@@ -212,30 +254,51 @@ pub struct MutexGuard<'a, T> {
 
 impl<T> std::ops::Deref for MutexGuard<'_, T> {
     type Target = T;
-    fn deref(&self) -> &T { self.value.as_ref().expect("MutexGuard: value missing") }
+    fn deref(&self) -> &T {
+        match self.value.as_ref() {
+            Some(v) => v,
+            None => panic!("smarm: MutexGuard value missing (core corrupt)"),
+        }
+    }
 }
 
 impl<T> std::ops::DerefMut for MutexGuard<'_, T> {
     fn deref_mut(&mut self) -> &mut T {
-        self.value.as_mut().expect("MutexGuard: value missing")
+        match self.value.as_mut() {
+            Some(v) => v,
+            None => panic!("smarm: MutexGuard value missing (core corrupt)"),
+        }
     }
 }
 
 impl<T: std::fmt::Debug> std::fmt::Debug for MutexGuard<'_, T> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let value = match self.value.as_ref() {
+            Some(v) => v,
+            None => panic!("smarm: MutexGuard value missing (core corrupt)"),
+        };
         f.debug_tuple("MutexGuard")
-            .field(self.value.as_ref().expect("MutexGuard: value missing"))
+            .field(value)
             .finish()
     }
 }
 
 impl<T> Drop for MutexGuard<'_, T> {
     fn drop(&mut self) {
-        let v = self.value.take().expect("MutexGuard: double drop");
-        *self.mutex.value.lock().unwrap() = Some(v);
+        let v = match self.value.take() {
+            Some(v) => v,
+            None => panic!("smarm: MutexGuard double drop (core corrupt)"),
+        };
+        match self.mutex.value.lock() {
+            Ok(mut g) => *g = Some(v),
+            Err(e) => panic!("smarm: mutex value lock poisoned (core corrupt): {e}"),
+        }
 
         let next = {
-            let mut st = self.mutex.core.state.lock().unwrap();
+            let mut st = match self.mutex.core.state.lock() {
+                Ok(g) => g,
+                Err(e) => panic!("smarm: mutex state lock poisoned (core corrupt): {e}"),
+            };
             match st.waiters.pop_front() {
                 Some(w) => {
                     st.holder = Some(w.pid);

src/pg.rs

@@ -1,15 +1,17 @@
-//! Process groups — a `name → multiset<Member>` map (RFC 012).
+//! Process groups: one name, many actors.
 //!
-//! Sits parallel to [`registry`](crate::registry), not on top of it. The
-//! registry is a *bimap*: at most one pid per name. A group is the opposite —
-//! many pids per name, the same pid in many groups — so it cannot be a
-//! generalization of the bimap; it is its own keyspace sharing only the
-//! liveness signal source (monitors) and the lock *class*.
+//! A process group is a named set of actors that you can look up, fan out to,
+//! or pick a worker from. It is the natural home for a *worker pool* (several
+//! interchangeable actors doing the same job), for *service discovery* (find
+//! everyone currently offering some capability), and for *broadcast* (reach
+//! every member of a group at once).
 //!
-//! ## Example
+//! The set is *live*: members [`join`] it, and a member that dies is removed
+//! automatically. You never deregister a dead actor — there is no bookkeeping
+//! to get wrong, and [`members`] / [`pick`] never hand you an actor that has
+//! already gone.
 //!
-//! A group is a live membership view: members join, and a member that dies is
-//! evicted automatically — no deregistration call, no bookkeeping.
+//! ## Joining and reading a group
 //!
 //! ```
 //! use smarm::{channel, join, leave, members, pick, run, spawn};
@@ -25,8 +27,8 @@
 //!     join("pool", w2.pid());
 //!     assert_eq!(members("pool").len(), 2);
 //!
-//!     // One worker dies. Nobody told the group — the death hook evicts it,
-//!     // so it is gone from `members` and never returned by `pick`.
+//!     // One worker dies. Nothing tells the group — smarm evicts it
+//!     // automatically, so it is gone from `members` and never picked.
 //!     tx1.send(()).unwrap();
 //!     w1.join().unwrap();
 //!     assert_eq!(members("pool"), vec![w2.pid()]);
@@ -41,60 +43,72 @@
 //! });
 //! ```
 //!
-//! ## Cleanup is eager and monitor-driven (unlike the registry)
+//! [`members`] returns every live member in the order they joined; [`pick`]
+//! returns one of them, or `None` when the group is empty. The same actor can
+//! belong to any number of groups at once, and joining a group it is already in
+//! is a harmless no-op.
 //!
-//! The registry prunes a stale binding lazily, on contact, because it only
-//! ever resolves one binding at a time. A group is *iterated* — `members` fans
-//! out to every member — so it must not carry dead members across a broadcast.
-//! Each [`join`] installs a `monitor(pid)` and keeps the resulting [`Monitor`]
-//! *alongside the group entry*; the actor's one-shot `Down` lands in that
-//! monitor's channel when it dies. Every group operation [`reap`s][reap] the
-//! group it touches first — draining each membership's monitor with a
-//! non-blocking `try_recv` — and on the first sign of death sweeps that pid out
-//! of *every* group via the predicate primitive. So the set is self-pruning on
-//! contact rather than filtered on read; the read path additionally applies a
-//! generation-checked liveness backstop so a member already dead but not yet
-//! reaped is never *returned*, even though eviction remains the monitor's job.
+//! ## Membership ends on its own
 //!
-//! [reap]: ProcessGroups::reap_group
+//! You do not have to clean up after a member that dies. When an actor exits —
+//! for any reason — it is removed from every group it had joined, before any
+//! later read or send can observe it. [`leave`] is only for *voluntary*
+//! departure, when a still-living actor wants out of a group.
 //!
-//! ## Eviction is one dumb primitive
+//! This is the main difference from keeping your own `Vec<Pid>`: a plain list
+//! goes stale the instant a member dies, and you would have to notice and prune
+//! it yourself. A group prunes itself.
 //!
-//! [`ProcessGroups::remove_where`] removes every member matching a predicate
-//! from every group. The primitive never knows *why* a member leaves — that is
-//! the caller's concern. Its first caller is the monitor death hook (this RFC,
-//! via `reap_group`); the later `evict_incarnation(node, inc)` sweep (RFC 010)
-//! reuses the same predicate path, which is the whole reason to shape it as a
-//! predicate.
+//! ## Sending to a group
 //!
-//! ## Identity is cluster-shaped from the first commit
+//! For a worker pool you usually want to hand a job to *one* available member.
+//! [`dispatch`] picks a live member and sends it a message in a single step,
+//! returning the member it reached:
 //!
-//! A [`Member`] is not a bare [`Pid`]: it is `(NodeId, Incarnation, Pid)`, a
-//! field-for-field image of a modern BEAM pid (`NEW_PID_EXT`) so the eventual
-//! ETF codec (RFC 011) is a near-identity mapping. In this RFC `NodeId` and
-//! `Incarnation` are runtime-init constants — one node, one fixed incarnation
-//! — threaded through storage and eviction anyway so the public surface never
-//! has to change to acquire them once clustering (RFC 010) supplies real
-//! values. No cluster types leak out of the public functions: callers pass and
-//! receive [`Pid`]; the node/incarnation are filled from runtime identity.
+//! ```ignore
+//! use smarm::{dispatch, join, Addressable};
 //!
-//! ## Locking
+//! struct Job(String);
+//! struct Worker;
+//! impl Addressable for Worker { type Msg = Job; }
 //!
-//! One `RawMutex` (Leaf class) on `RuntimeInner`, mirroring `registry`. The
-//! group lock is never held with another Leaf (it never touches the registry
-//! or a slot's cold lock). The two places that *do* need another lock are kept
-//! off the group-lock path:
+//! // Each worker has published a `Pid<Worker>` inbox and joined the pool.
+//! join("workers", worker_a);
+//! join("workers", worker_b);
 //!
-//!   - `monitor()` / `demonitor()` acquire the target's cold lock (Leaf) and
-//!     so run *before* / *after* the group lock, never under it.
-//!   - draining a monitor with `try_recv` takes the channel's Channel-class
-//!     lock — permitted *under* a Leaf by the lock order (`raw_mutex.rs`), and
-//!     a channel critical section only does the lock-free unpark protocol, so
-//!     no Leaf is ever nested under it.
+//! // Route one job to whichever live worker `pick` lands on.
+//! match dispatch::<Worker>("workers", Job("resize image".into())) {
+//!     Ok(who) => println!("sent to {who:?}"),
+//!     Err(returned) => println!("no worker took it: {returned:?}"),
+//! }
+//! ```
 //!
-//! Evicted and rejected [`Monitor`]s are dropped only *after* the group lock is
-//! released, so a receiver-drop never runs a wakeup under the lock (same
-//! discipline as `demonitor`).
+//! When you want the pids themselves rather than to send right away, [`pick_as`]
+//! and [`members_as`] return typed [`Pid<A>`](Pid)s for a homogeneous group, so
+//! the follow-up send stays compile-checked. The untyped [`pick`] and
+//! [`members`] are for mixed groups, where all you can rely on is identity.
+//!
+//! ## Groups vs. the registry
+//!
+//! A group is the many-actors counterpart to the [`registry`](crate::registry).
+//! The registry binds a name to *at most one* actor and re-resolves it on every
+//! send — what you want for a single well-known service. A group binds a name to
+//! *many* actors, and one actor may sit in many groups. Reach for the registry
+//! when there is exactly one of something; reach for a group when there is a set.
+//!
+//! ## Identity and clustering
+//!
+//! A group member is described by a [`Member`] — a [`Pid`] plus a [`NodeId`] and
+//! an [`Incarnation`]. Today everything is single-node, those two fields are
+//! fixed defaults, and you only ever pass and receive a plain [`Pid`]: the extra
+//! identity is carried so this API will not have to change when groups learn to
+//! span a cluster.
+//!
+//! ## Running context
+//!
+//! Every function here addresses the current runtime, so each must be called
+//! from inside [`run`](crate::run) (that is, on an actor thread). Calling one
+//! from outside a running runtime panics.
 
 use crate::monitor::{demonitor, monitor, Monitor};
 use crate::pid::{assert_type, Addressable, Pid};
@@ -103,7 +117,7 @@ use crate::scheduler::with_runtime;
 use std::collections::HashMap;
 
 /// A cluster node handle. A `u32` integer handle, *not* an interned atom — the
-/// single deliberate divergence from the BEAM wire shape (RFC 011 names it).
+/// single deliberate divergence from the BEAM wire shape.
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub struct NodeId(u32);
 
@@ -149,9 +163,8 @@ impl From<u32> for Incarnation {
     }
 }
 
-/// The fixed single-node identity used until clustering (RFC 010) supplies
-/// real values. Carried like `wake_slot` so the public API never has to change
-/// to acquire it.
+/// The fixed single-node identity used until clustering supplies real values.
+/// Carried like `wake_slot` so the public API never has to change to acquire it.
 pub const DEFAULT_NODE_ID: NodeId = NodeId(0);
 /// The fixed incarnation for the single-node default. Non-zero so it never
 /// collides with a BEAM "any creation" wildcard at interop time.
@@ -161,7 +174,7 @@ pub const DEFAULT_INCARNATION: Incarnation = Incarnation(1);
 ///
 /// Deliberately a field-for-field image of a modern BEAM pid (`NEW_PID_EXT`).
 /// In memory it is a plain struct — no wire packing; the packed representation
-/// belongs to the `RemoteRef` boundary (RFC 010/011), not here.
+/// belongs to the remote-reference boundary, not here.
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 pub struct Member {
     /// Which node the pid lives on. `DEFAULT_NODE_ID` while single-node.
@@ -174,7 +187,7 @@ pub struct Member {
 }
 
 /// One membership: a [`Member`] and the [`Monitor`] that watches its liveness.
-/// The monitor lives *alongside* the group entry (RFC 012) so a group is
+/// The monitor lives *alongside* the group entry so a group is
 /// self-contained: draining the membership tells us whether the member is
 /// still alive, and dropping the membership drops its monitor.
 struct Membership {
@@ -185,7 +198,23 @@ struct Membership {
 /// The store: `name → multiset<Member>`. Within a single group a `Member`
 /// appears at most once (`join` is idempotent); the *multiset* framing is for
 /// cluster-readiness — the same pid is freely a member of many groups, and the
-/// width admits multiples in general. Held under one Leaf-class `RawMutex`.
+/// width admits multiples in general.
+///
+/// Locking discipline. Held under one Leaf-class `RawMutex` on `RuntimeInner`,
+/// mirroring the registry, and never held together with another Leaf lock (it
+/// never touches the registry or a slot's cold lock). The two operations that
+/// do need another lock are kept off the group-lock path:
+///
+///   - `monitor()` / `demonitor()` take the target's cold lock (also Leaf), so
+///     they run *before* / *after* the group lock, never under it.
+///   - draining a monitor with `try_recv` takes the channel's Channel-class
+///     lock, which the lock order permits *under* a Leaf; a channel critical
+///     section only does the lock-free unpark protocol, so no Leaf ever nests
+///     under it.
+///
+/// Evicted and rejected [`Monitor`]s are therefore dropped only *after* the
+/// group lock is released, so a receiver-drop never runs a wakeup under the
+/// lock — the same discipline as `demonitor`.
 pub(crate) struct ProcessGroups {
     groups: HashMap<String, Vec<Membership>>,
 }
@@ -223,9 +252,11 @@ impl ProcessGroups {
     /// The one dumb eviction primitive: drop every member matching `pred` from
     /// every group, pruning emptied groups, and return the evicted memberships'
     /// monitors for the caller to drop outside the lock. The primitive does not
-    /// know *why* a member leaves. Callers: the death hook (`reap_group`) and,
-    /// later, `evict_incarnation` (RFC 010), over the same path. Insertion
-    /// order within a group is preserved (`members` / `pick` are order-stable).
+    /// know *why* a member leaves; that is the caller's concern. Its callers are
+    /// the death hook (`reap_group`) and, once clustering lands, an
+    /// incarnation-eviction sweep — both over this same predicate path, which is
+    /// the whole reason to shape eviction as a predicate. Insertion order within
+    /// a group is preserved (`members` / `pick` are order-stable).
     fn remove_where(&mut self, mut pred: impl FnMut(&Member) -> bool) -> Vec<Monitor> {
         let mut evicted = Vec::new();
         self.groups.retain(|_, v| {
@@ -242,12 +273,18 @@ impl ProcessGroups {
         evicted
     }
 
-    /// Drain-on-contact death hook. Drains every membership monitor in `group`
-    /// with a non-blocking `try_recv`: a delivered `Down` (any reason) or a
-    /// closed channel means that member is dead. On the first death detected,
-    /// sweep *all* of the dead pids out of *every* group via [`remove_where`]
-    /// — a death is removed from each group it joined, not just the one being
-    /// touched. Returns the evicted monitors to drop outside the lock.
+    /// Drain-on-contact death hook. The registry can prune a stale binding
+    /// lazily, on contact, because it only ever resolves one binding at a time;
+    /// a group is *iterated* — `members` fans out to everyone — so it must not
+    /// carry a dead member across a broadcast. Every group operation reaps the
+    /// group it touches first.
+    ///
+    /// Drains every membership monitor in `group` with a non-blocking
+    /// `try_recv`: a delivered `Down` (any reason) or a closed channel means
+    /// that member is dead. On the first death detected, sweep *all* of the
+    /// dead pids out of *every* group via [`remove_where`] — a death is removed
+    /// from each group it joined, not just the one being touched. Returns the
+    /// evicted monitors to drop outside the lock.
     fn reap_group(&mut self, group: &str) -> Vec<Monitor> {
         let dead: Vec<Pid> = {
             let Some(v) = self.groups.get(group) else {
@@ -279,7 +316,7 @@ impl ProcessGroups {
     }
 
     /// Live members of `group`, in insertion order. The `is_live` oracle is the
-    /// read-path backstop (Phase 3): a member whose slot is already dead is
+    /// read-path backstop: a member whose slot is already dead is
     /// dropped from the *result* even if its `Down` has not been drained yet.
     /// Backstop only — the entry stays in storage; eviction is the monitor's
     /// job (`reap_group`).
@@ -314,18 +351,19 @@ fn live(inner: &crate::runtime::RuntimeInner, pid: Pid) -> bool {
 /// pid is a member at most once (idempotent). Returns `true` if this call newly
 /// added the membership, `false` if it was already a member.
 ///
-/// Installs a `monitor(pid)` whose one-shot `Down` drives eviction: the
-/// registration races `finalize_actor` under the slot's cold lock exactly as
-/// every other monitor does, so no death slips between the join and the
-/// registration. A redundant (idempotent) join tears its extra monitor back
-/// down.
+/// Installs a monitor on `pid` so the actor's death evicts it from the group
+/// automatically — you never have to remove a dead member yourself. A redundant
+/// (idempotent) join tears its extra monitor back down.
 ///
 /// Panics if called outside `Runtime::run()`.
 pub fn join<A>(group: impl Into<String>, pid: Pid<A>) -> bool {
     let group = group.into();
     let pid = pid.erase();
     // Install the monitor BEFORE taking the group lock: monitor() acquires the
-    // target's cold lock (Leaf), and two Leaf locks are never held at once.
+    // target's cold lock (Leaf), and two Leaf locks are never held at once. The
+    // registration races `finalize_actor` under that cold lock exactly as every
+    // other monitor does, so no death can slip between the join and the monitor
+    // being in place.
     let mon = monitor(pid);
 
     let (rejected, reaped) = with_runtime(|inner| {
@@ -372,12 +410,13 @@ pub fn leave<A>(group: &str, pid: Pid<A>) -> bool {
     }
 }
 
-/// Fan-out read: every live member of `group`.
+/// Every live member of `group`, in the order they joined. Returns an empty
+/// vector if the group does not exist or has no live members.
 ///
-/// The touched group is reaped first, so dead members are evicted before the
-/// read. The generation-checked liveness read is a belt-and-braces backstop:
-/// even in the finalize window where a member is already dead but its `Down`
-/// has not yet landed, it is dropped from the result.
+/// Dead members are never returned: the group is pruned of anything that has
+/// died before the read, and as a backstop a member whose slot is already dead
+/// is dropped from the result even in the brief window before its death has
+/// been fully processed.
 ///
 /// Panics if called outside `Runtime::run()`.
 pub fn members(group: &str) -> Vec<Pid> {
@@ -391,11 +430,10 @@ pub fn members(group: &str) -> Vec<Pid> {
     pids
 }
 
-/// Pool/discovery read: one live member of `group`, or `None` if empty.
-/// Stateless first-live selection: the touched group is reaped first, and the
-/// generation-checked liveness backstop skips any member already dead but not
-/// yet reaped. Smarter routing is an explicitly later, clustered concern per
-/// RFC 010.
+/// One live member of `group`, or `None` if the group is empty (or every
+/// member has died). Selection is a stateless first-live scan in join order,
+/// with the same dead-member backstop as [`members`]; smarter, load-aware
+/// routing is a later, clustered concern.
 ///
 /// Panics if called outside `Runtime::run()`.
 pub fn pick(group: &str) -> Option<Pid> {
@@ -409,11 +447,11 @@ pub fn pick(group: &str) -> Option<Pid> {
     picked
 }
 
-/// Typed `pick`: one live member of `group` as a [`Pid<A>`] (RFC 014 §4.4).
+/// Typed [`pick`]: one live member of `group` as a [`Pid<A>`](Pid).
 /// For a homogeneous pool every member is an `A`, so the picked member comes
 /// back typed and dispatch is an ordinary compile-checked [`send_to`] rather
 /// than the [`send_dyn`](crate::send_dyn) escape hatch. Re-types via the
-/// unchecked [`assert_type`] primitive — a wrong `A` degrades to
+/// unchecked `assert_type` primitive — a wrong `A` degrades to
 /// [`SendError::NoChannel`] on the next send, never a misdelivery.
 ///
 /// Panics if called outside `Runtime::run()`.

src/registry.rs

@@ -193,11 +193,12 @@ impl Mailbox {
     /// legal under a Leaf (Leaf -> Channel).
     fn clone_sender<M: Send + 'static>(&self) -> Option<Sender<M>> {
         let ch = self.channels.get(&TypeId::of::<M>())?;
-        let tx = ch
-            .sender
-            .as_any()
-            .downcast_ref::<Sender<M>>()
-            .expect("channel keyed by TypeId but downcast to its own type failed — smarm bug");
+        let tx = match ch.sender.as_any().downcast_ref::<Sender<M>>() {
+            Some(tx) => tx,
+            None => panic!(
+                "smarm: channel keyed by TypeId but downcast to its own type failed (core corrupt)"
+            ),
+        };
         debug_assert_eq!(ch.msg_type, type_name::<M>(), "msg_type / TypeId disagree");
         Some(tx.clone())
     }

src/run_queue.rs

@@ -113,16 +113,32 @@ impl MutexQueue {
 
     pub fn push(&self, pid: Pid) {
         assert_no_preempt();
-        self.q.lock().unwrap().push_back(pid);
+        match self.q.lock() {
+            Ok(mut g) => g.push_back(pid),
+            Err(e) => panic!("smarm: run-queue q lock poisoned (core corrupt): {e}"),
+        }
     }
 
     pub fn pop(&self) -> Option<Pid> {
         assert_no_preempt();
-        self.q.lock().unwrap().pop_front()
+        match self.q.lock() {
+            Ok(mut g) => g.pop_front(),
+            Err(e) => panic!("smarm: run-queue q lock poisoned (core corrupt): {e}"),
+        }
     }
 
     pub fn len(&self) -> u64 {
-        self.q.lock().unwrap().len() as u64
+        match self.q.lock() {
+            Ok(g) => g.len() as u64,
+            Err(e) => panic!("smarm: run-queue q lock poisoned (core corrupt): {e}"),
+        }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        match self.q.lock() {
+            Ok(g) => g.is_empty(),
+            Err(e) => panic!("smarm: run-queue q lock poisoned (core corrupt): {e}"),
+        }
     }
 }
 
@@ -262,6 +278,10 @@ impl MpmcRing {
         let d = self.dequeue_pos.0.load(Ordering::Relaxed);
         e.saturating_sub(d) as u64
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
 }
 
 // ---------------------------------------------------------------------------
@@ -341,6 +361,10 @@ impl StripedRing {
     pub fn len(&self) -> u64 {
         self.stripes.iter().map(|s| s.len()).sum()
     }
+
+    pub fn is_empty(&self) -> bool {
+        self.stripes.iter().all(|s| s.is_empty())
+    }
 }
 
 // ---------------------------------------------------------------------------

src/runtime.rs

@@ -655,6 +655,9 @@ pub(crate) struct RuntimeInner {
 }
 
 impl RuntimeInner {
+    // Private constructor taking the parsed Config fields one-for-one; a params
+    // struct would only move the same 8 values across the call boundary.
+    #[allow(clippy::too_many_arguments)]
     fn new(
         thread_count: usize,
         alloc_interval: u32,
@@ -762,7 +765,10 @@ impl RuntimeInner {
     /// park-epoch and return it. See slot_state.rs for the rules.
     #[must_use]
     pub(crate) fn begin_wait(&self, pid: Pid) -> u32 {
-        let slot = self.slot_at(pid).expect("begin_wait: own slot vanished");
+        let slot = match self.slot_at(pid) {
+            Some(slot) => slot,
+            None => panic!("begin_wait: own slot vanished: {:?}", pid),
+        };
         slot.word.begin_wait(pid.generation())
     }
 
@@ -771,7 +777,10 @@ impl RuntimeInner {
     /// then eat a notification that already landed. The caller MUST
     /// re-check its stop flag afterwards — see `StateWord::clear_notify`.
     pub(crate) fn retire_wait(&self, pid: Pid) {
-        let slot = self.slot_at(pid).expect("retire_wait: own slot vanished");
+        let slot = match self.slot_at(pid) {
+            Some(slot) => slot,
+            None => panic!("retire_wait: own slot vanished: {:?}", pid),
+        };
         let _ = slot.word.begin_wait(pid.generation());
         slot.word.clear_notify(pid.generation());
     }
@@ -932,7 +941,14 @@ impl Runtime {
             self.inner.live_actors.load(Ordering::Acquire), 0,
             "run() called while previous run still active"
         );
-        *self.inner.io.lock().unwrap() = Some(IoThread::start().expect("failed to start IO thread"));
+        let io_thread = match IoThread::start() {
+            Ok(io) => io,
+            Err(e) => panic!("failed to start IO thread: {e}"),
+        };
+        match self.inner.io.lock() {
+            Ok(mut io) => *io = Some(io_thread),
+            Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
+        }
 
         // RFC 005: slot counters reset at the START of a run (not the end),
         // so `stats()` read after `run()` returns reports that run's totals.
@@ -977,8 +993,14 @@ impl Runtime {
         drop(initial_handle);
 
         // Tear down IO and clean up for the next run() call.
-        drop(self.inner.io.lock().unwrap().take()); // joins IO threads
-        self.inner.timers.lock().unwrap().clear();
+        match self.inner.io.lock() {
+            Ok(mut io) => drop(io.take()), // joins IO threads
+            Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
+        }
+        match self.inner.timers.lock() {
+            Ok(mut timers) => timers.clear(),
+            Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+        }
         self.inner.next_monitor_id.store(0, Ordering::Relaxed);
         // Every slot must have come back: any leak here is a runtime bug
         // (a JoinHandle held across run() is decremented just above).
@@ -1156,10 +1178,16 @@ fn finalize_actor(inner: &Arc<RuntimeInner>, pid: Pid, outcome: Outcome) {
         Outcome::Stopped => (Outcome::Stopped, Signal::Stopped(pid), DownReason::Stopped),
     };
 
-    let slot = inner.slot_at(pid).expect("finalize_actor: pid out of range");
+    let slot = match inner.slot_at(pid) {
+        Some(slot) => slot,
+        None => panic!("finalize_actor: pid out of range: {:?}", pid),
+    };
     let (waiters, monitors, links, actor) = {
         let mut cold = slot.cold.lock();
-        let actor = cold.actor.take().expect("finalize_actor: actor vanished");
+        let actor = match cold.actor.take() {
+            Some(actor) => actor,
+            None => panic!("finalize_actor: actor vanished"),
+        };
         cold.outcome = Some(joiner_outcome);
         slot.stop_ptr.store(std::ptr::null_mut(), Ordering::Release);
         // Done is published under the cold lock, so join's
@@ -1301,17 +1329,23 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot_idx: usize) {
             // just to discover there is nothing to drain. The clock is read
             // only when the timer heap is non-empty.
             let due = {
-                let mut t = inner.timers.lock().unwrap();
+                let mut t = match inner.timers.lock() {
+                    Ok(t) => t,
+                    Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+                };
                 if t.is_empty() {
                     Vec::new()
                 } else {
                     t.pop_due(std::time::Instant::now())
                 }
             };
-            let completions = inner.io.lock().unwrap()
-                .as_mut()
-                .map(|io| io.drain_completions())
-                .unwrap_or_default();
+            let completions = match inner.io.lock() {
+                Ok(mut io) => io
+                    .as_mut()
+                    .map(|io| io.drain_completions())
+                    .unwrap_or_default(),
+                Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
+            };
             for entry in due {
                 match entry.reason {
                     // A sleep expiry is just an unpark: the protocol handles
@@ -1340,8 +1374,15 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot_idx: usize) {
             for completion in completions {
                 match completion {
                     crate::io::Completion::Blocking { pid, epoch, result } => {
-                        if let Some(io) = inner.io.lock().unwrap().as_mut() {
-                            io.outstanding = io.outstanding.saturating_sub(1);
+                        match inner.io.lock() {
+                            Ok(mut io) => {
+                                if let Some(io) = io.as_mut() {
+                                    io.outstanding = io.outstanding.saturating_sub(1);
+                                }
+                            }
+                            Err(e) => {
+                                panic!("smarm: io lock poisoned (core corrupt): {e}")
+                            }
                         }
                         // Stash the result under the cold lock, then unpark.
                         // The protocol also covers the submit→park window
@@ -1363,11 +1404,16 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot_idx: usize) {
                     crate::io::Completion::FdReady { fd, events: _ } => {
                         // Resolve the parked pid under the io lock, then wake
                         // through the protocol. Lock order: io before all.
-                        let parked = inner.io.lock().unwrap().as_mut().and_then(|io| {
-                            let entry = io.waiters.remove(&fd);
-                            io.epoll_deregister(fd);
-                            entry
-                        });
+                        let parked = match inner.io.lock() {
+                            Ok(mut io) => io.as_mut().and_then(|io| {
+                                let entry = io.waiters.remove(&fd);
+                                io.epoll_deregister(fd);
+                                entry
+                            }),
+                            Err(e) => {
+                                panic!("smarm: io lock poisoned (core corrupt): {e}")
+                            }
+                        };
                         if let Some((pid, epoch)) = parked {
                             inner.unpark_at(pid, epoch);
                         }
@@ -1411,9 +1457,15 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot_idx: usize) {
             // Read IO liveness BEFORE the queue lock (phase-1 ordering: a
             // completion resurrects an actor only via the drain path, whose
             // enqueue would be visible under the queue lock we take next).
-            let (io_out, io_fd) = match inner.io.lock().unwrap().as_ref() {
-                Some(io) => (io.outstanding + io.waiters.len() as u32, Some(io.wake_fd())),
-                None => (0, None),
+            let (io_out, io_fd) = {
+                let io = match inner.io.lock() {
+                    Ok(io) => io,
+                    Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
+                };
+                match io.as_ref() {
+                    Some(io) => (io.outstanding + io.waiters.len() as u32, Some(io.wake_fd())),
+                    None => (0, None),
+                }
             };
 
             stats.run_queue_len.store(inner.run_queue.len(), Ordering::Relaxed);
@@ -1457,7 +1509,10 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot_idx: usize) {
                     // Remaining timer entries are orphaned (no live actor can be
                     // woken by them — e.g. a sleeper cancelled out of its sleep);
                     // they must not keep the runtime alive. Drop them on the way out.
-                    inner.timers.lock().unwrap().clear();
+                    match inner.timers.lock() {
+                        Ok(mut timers) => timers.clear(),
+                        Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+                    }
                     // Terminal wake: a sibling scheduler may be blocked in its
                     // idle wait on a snapshot that is now terminally stale — an
                     // orphaned long deadline (it would sleep it out in full) or
@@ -1466,8 +1521,13 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot_idx: usize) {
                     // no completion, so nothing else writes the wake pipe).
                     // One byte wakes every poller; each re-runs the verdict,
                     // reaches AllDone itself, and re-wakes — idempotent.
-                    if let Some(io) = inner.io.lock().unwrap().as_ref() {
-                        io.wake();
+                    match inner.io.lock() {
+                        Ok(io) => {
+                            if let Some(io) = io.as_ref() {
+                                io.wake();
+                            }
+                        }
+                        Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
                     }
                     return;
                 }
@@ -1481,7 +1541,10 @@ fn schedule_loop(inner: &Arc<RuntimeInner>, slot_idx: usize) {
                 Pop::Idle { io_outstanding, wake_fd } => {
                     // Something is still in flight. Sleep on the appropriate
                     // source to avoid hammering the queue mutex; retry on wake.
-                    let next_deadline = inner.timers.lock().unwrap().peek_deadline();
+                    let next_deadline = match inner.timers.lock() {
+                        Ok(timers) => timers.peek_deadline(),
+                        Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+                    };
                     match (next_deadline, wake_fd) {
                         (Some(deadline), fd_opt) => {
                             let now = std::time::Instant::now();

src/scheduler.rs

@@ -39,7 +39,10 @@ pub(crate) fn with_runtime<R>(f: impl FnOnce(&Arc<RuntimeInner>) -> R) -> R {
     let prev = crate::preempt::PREEMPTION_ENABLED.with(|c| c.replace(false));
     let result = RUNTIME.with(|r| {
         let b = r.borrow();
-        let inner = b.as_ref().expect("smarm: not inside Runtime::run()");
+        let inner = match b.as_ref() {
+            Some(inner) => inner,
+            None => panic!("smarm: not inside Runtime::run()"),
+        };
         f(inner)
     });
     crate::preempt::PREEMPTION_ENABLED.with(|c| c.set(prev));
@@ -51,7 +54,7 @@ pub(crate) fn with_runtime<R>(f: impl FnOnce(&Arc<RuntimeInner>) -> R) -> R {
 /// Same preemption gate as [`with_runtime`]; same reasons.
 pub(crate) fn try_with_runtime<R>(f: impl FnOnce(&Arc<RuntimeInner>) -> R) -> Option<R> {
     let prev = crate::preempt::PREEMPTION_ENABLED.with(|c| c.replace(false));
-    let result = RUNTIME.with(|r| r.borrow().as_ref().map(|inner| f(inner)));
+    let result = RUNTIME.with(|r| r.borrow().as_ref().map(f));
     crate::preempt::PREEMPTION_ENABLED.with(|c| c.set(prev));
     result
 }
@@ -76,15 +79,20 @@ impl JoinHandle {
     pub fn join(mut self) -> Result<(), JoinError> {
         use crate::actor::Outcome;
 
-        let me = current_pid().expect("join() called outside an actor");
+        let me = match current_pid() {
+            Some(pid) => pid,
+            None => panic!("join() called outside an actor"),
+        };
 
         loop {
             // Check-Done-or-register-waiter is atomic under the target's cold
             // lock; finalize publishes Done and takes the waiter list under
             // the same lock, so we either see the outcome or are woken.
             let outcome = with_runtime(|inner| {
-                let slot = inner.slot_at(self.pid)
-                    .expect("join: pid index out of range");
+                let slot = match inner.slot_at(self.pid) {
+                    Some(slot) => slot,
+                    None => panic!("join: pid index out of range: {:?}", self.pid),
+                };
                 let mut cold = slot.cold.lock();
                 match slot.status_for(self.pid) {
                     // Our outstanding handle pins the slot: it cannot be
@@ -93,7 +101,10 @@ impl JoinHandle {
                         panic!("join: target slot has been reused")
                     }
                     crate::slot_state::Status::Done => {
-                        Some(cold.outcome.take().expect("Done slot must have outcome"))
+                        Some(match cold.outcome.take() {
+                            Some(outcome) => outcome,
+                            None => panic!("Done slot must have outcome"),
+                        })
                     }
                     crate::slot_state::Status::Live => {
                         // begin_wait is lock-free, legal under the cold lock;
@@ -181,8 +192,10 @@ pub fn spawn_under<A>(supervisor: Pid<A>, f: impl FnOnce() + Send + 'static) ->
     // syscall and no allocation ever stalls another scheduler thread.
     let stack = with_runtime(|inner| inner.stack_pool.lock().pop())
         .unwrap_or_else(|| {
-            crate::stack::Stack::new(crate::runtime::ACTOR_STACK_SIZE)
-                .expect("stack allocation failed")
+            match crate::stack::Stack::new(crate::runtime::ACTOR_STACK_SIZE) {
+                Ok(stack) => stack,
+                Err(e) => panic!("stack allocation failed: {e}"),
+            }
         });
     let sp = init_actor_stack(stack.top(), crate::actor::trampoline);
     let closure: crate::runtime::Closure = Box::new(f);
@@ -225,7 +238,10 @@ pub fn spawn_addr<A: crate::pid::Addressable>(
 use crate::context::init_actor_stack;
 
 pub fn self_pid() -> Pid {
-    current_pid().expect("self_pid() called outside an actor")
+    match current_pid() {
+        Some(pid) => pid,
+        None => panic!("self_pid() called outside an actor"),
+    }
 }
 
 // ---------------------------------------------------------------------------
@@ -282,7 +298,10 @@ pub(crate) fn unpark_at(pid: Pid, epoch: u32) {
 /// waker. Lock-free (one CAS on the own slot word), so it is legal under
 /// any lock, including a Channel-class lock.
 pub(crate) fn begin_wait() -> u32 {
-    let me = current_pid().expect("begin_wait() called outside an actor");
+    let me = match current_pid() {
+        Some(pid) => pid,
+        None => panic!("begin_wait() called outside an actor"),
+    };
     with_runtime(|inner| inner.begin_wait(me))
 }
 
@@ -294,7 +313,10 @@ pub(crate) fn begin_wait() -> u32 {
 /// self-clean at their wakers' failed CAS; nothing can fault the actor's
 /// next one-shot park.
 pub(crate) fn retire_wait() {
-    let me = current_pid().expect("retire_wait() called outside an actor");
+    let me = match current_pid() {
+        Some(pid) => pid,
+        None => panic!("retire_wait() called outside an actor"),
+    };
     with_runtime(|inner| inner.retire_wait(me));
     // A request_stop that fired before the clear had its notification
     // eaten, but it set the stop flag first — observe it here and unwind.
@@ -365,11 +387,19 @@ impl Drop for NoPreempt {
 // ---------------------------------------------------------------------------
 
 pub fn sleep(duration: std::time::Duration) {
-    let me = current_pid().expect("sleep() called outside an actor");
+    let me = match current_pid() {
+        Some(pid) => pid,
+        None => panic!("sleep() called outside an actor"),
+    };
     let _np = NoPreempt::enter();
     let epoch = begin_wait();
     let deadline = crate::timer::deadline_from_now(duration);
-    with_runtime(|inner| inner.timers.lock().unwrap().insert_sleep(deadline, me, epoch));
+    with_runtime(|inner| {
+        match inner.timers.lock() {
+            Ok(mut timers) => timers.insert_sleep(deadline, me, epoch),
+            Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+        }
+    });
     park_current();
 }
 
@@ -380,11 +410,14 @@ pub fn insert_wait_timer(
     epoch: u32,
 ) {
     with_runtime(|inner| {
-        inner.timers.lock().unwrap().insert(
-            deadline,
-            pid,
-            crate::timer::Reason::WaitTimeout { target, epoch },
-        );
+        match inner.timers.lock() {
+            Ok(mut timers) => timers.insert(
+                deadline,
+                pid,
+                crate::timer::Reason::WaitTimeout { target, epoch },
+            ),
+            Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+        }
     });
 }
 
@@ -412,7 +445,12 @@ pub fn send_after<A: crate::pid::Addressable>(
     let fire = Box::new(move || {
         let _ = crate::registry::send_to(dest, msg);
     });
-    with_runtime(|inner| inner.timers.lock().unwrap().insert_send(deadline, dest.erase(), fire))
+    with_runtime(|inner| {
+        match inner.timers.lock() {
+            Ok(mut timers) => timers.insert_send(deadline, dest.erase(), fire),
+            Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+        }
+    })
 }
 
 /// Deliver `msg` to whichever actor holds the name `dest` at fire time
@@ -429,7 +467,12 @@ pub fn send_after_named<M: Send + 'static>(
     let fire = Box::new(move || {
         let _ = crate::registry::send(dest, msg);
     });
-    with_runtime(|inner| inner.timers.lock().unwrap().insert_send(deadline, armed_by, fire))
+    with_runtime(|inner| {
+        match inner.timers.lock() {
+            Ok(mut timers) => timers.insert_send(deadline, armed_by, fire),
+            Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+        }
+    })
 }
 
 /// Deliver `msg` onto a channel the caller owns after `after`, rather than to a
@@ -453,14 +496,24 @@ pub(crate) fn send_after_to<T: Send + 'static>(
     let fire = Box::new(move || {
         let _ = tx.send(msg);
     });
-    with_runtime(|inner| inner.timers.lock().unwrap().insert_send(deadline, armed_by, fire))
+    with_runtime(|inner| {
+        match inner.timers.lock() {
+            Ok(mut timers) => timers.insert_send(deadline, armed_by, fire),
+            Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+        }
+    })
 }
 
 /// Cancel a timer armed by [`send_after`] / [`send_after_named`]. Returns
 /// `true` if it was still pending (delivery now prevented), `false` if it had
 /// already fired or been cancelled.
 pub fn cancel_timer(id: crate::timer::TimerId) -> bool {
-    with_runtime(|inner| inner.timers.lock().unwrap().cancel(id))
+    with_runtime(|inner| {
+        match inner.timers.lock() {
+            Ok(mut timers) => timers.cancel(id),
+            Err(e) => panic!("smarm: timers lock poisoned (core corrupt): {e}"),
+        }
+    })
 }
 
 // ---------------------------------------------------------------------------
@@ -472,7 +525,10 @@ where
     F: FnOnce() -> T + Send + 'static,
     T: Send + 'static,
 {
-    let me = current_pid().expect("block_on_io() called outside an actor");
+    let me = match current_pid() {
+        Some(pid) => pid,
+        None => panic!("block_on_io() called outside an actor"),
+    };
     let work: Box<dyn FnOnce() -> crate::io::IoResult + Send> = Box::new(move || {
         let v: T = f();
         Ok(Box::new(v) as Box<dyn std::any::Any + Send>)
@@ -481,24 +537,37 @@ where
         let _np = NoPreempt::enter();
         let epoch = begin_wait();
         with_runtime(|inner| {
-            let mut io = inner.io.lock().unwrap();
-            io.as_mut().expect("io thread not started").submit(me, epoch, work);
+            let mut io = match inner.io.lock() {
+                Ok(io) => io,
+                Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
+            };
+            match io.as_mut() {
+                Some(io) => io.submit(me, epoch, work),
+                None => panic!("io thread not started"),
+            }
         });
         park_current();
     }
     let result = with_runtime(|inner| {
-        let slot = inner.slot_at(me).expect("block_on_io: own slot vanished");
+        let slot = match inner.slot_at(me) {
+            Some(slot) => slot,
+            None => panic!("block_on_io: own slot vanished"),
+        };
         let mut cold = slot.cold.lock();
         debug_assert_eq!(
             slot.generation(), me.generation(),
             "block_on_io: own slot reused mid-park"
         );
-        cold.pending_io_result
-            .take()
-            .expect("block_on_io: resumed without a result")
+        match cold.pending_io_result.take() {
+            Some(result) => result,
+            None => panic!("block_on_io: resumed without a result"),
+        }
     });
     match result {
-        Ok(any) => *any.downcast::<T>().expect("block_on_io: type mismatch"),
+        Ok(any) => match any.downcast::<T>() {
+            Ok(typed) => *typed,
+            Err(_) => panic!("block_on_io: type mismatch"),
+        },
         Err(payload) => std::panic::resume_unwind(payload),
     }
 }
@@ -512,12 +581,21 @@ pub fn wait_writable(fd: std::os::fd::RawFd) -> std::io::Result<()> {
 }
 
 fn wait_fd(fd: std::os::fd::RawFd, readable: bool, writable: bool) -> std::io::Result<()> {
-    let me = current_pid().expect("wait_*() called outside an actor");
+    let me = match current_pid() {
+        Some(pid) => pid,
+        None => panic!("wait_*() called outside an actor"),
+    };
     let _np = NoPreempt::enter();
     let epoch = begin_wait();
     with_runtime(|inner| {
-        let mut io = inner.io.lock().unwrap();
-        io.as_mut().expect("io thread not started").epoll_register(fd, me, epoch, readable, writable)
+        let mut io = match inner.io.lock() {
+            Ok(io) => io,
+            Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
+        };
+        match io.as_mut() {
+            Some(io) => io.epoll_register(fd, me, epoch, readable, writable),
+            None => panic!("io thread not started"),
+        }
     })?;
 
     // If a terminal stop unwinds us out of the park below, the registration
@@ -535,7 +613,10 @@ fn wait_fd(fd: std::os::fd::RawFd, readable: bool, writable: bool) -> std::io::R
     impl Drop for Dereg {
         fn drop(&mut self) {
             with_runtime(|inner| {
-                let mut io = inner.io.lock().unwrap();
+                let mut io = match inner.io.lock() {
+                    Ok(io) => io,
+                    Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
+                };
                 if let Some(io) = io.as_mut() {
                     if io.waiters.get(&self.fd) == Some(&(self.me, self.epoch)) {
                         io.waiters.remove(&self.fd);
@@ -597,10 +678,16 @@ impl crate::channel::Selectable for FdArm {
             return Ok(false);
         }
         with_runtime(|inner| {
-            let mut io = inner.io.lock().unwrap();
-            io.as_mut()
-                .expect("io thread not started")
-                .epoll_register(self.fd, pid, epoch, self.readable, self.writable)
+            let mut io = match inner.io.lock() {
+                Ok(io) => io,
+                Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
+            };
+            match io.as_mut() {
+                Some(io) => {
+                    io.epoll_register(self.fd, pid, epoch, self.readable, self.writable)
+                }
+                None => panic!("io thread not started"),
+            }
         })?;
         Ok(true)
     }
@@ -621,7 +708,10 @@ impl crate::channel::Selectable for FdArm {
     /// actor's fresh registration; in that case touch nothing.
     fn sel_unregister(&self, pid: Pid, epoch: u32) {
         with_runtime(|inner| {
-            let mut io = inner.io.lock().unwrap();
+            let mut io = match inner.io.lock() {
+                Ok(io) => io,
+                Err(e) => panic!("smarm: io lock poisoned (core corrupt): {e}"),
+            };
             if let Some(io) = io.as_mut() {
                 if io.waiters.get(&self.fd) == Some(&(pid, epoch)) {
                     io.waiters.remove(&self.fd);

src/supervisor.rs

@@ -1,16 +1,114 @@
-//! Supervision signals.
+//! Supervision: keep a set of actors alive.
 //!
-//! Every actor has a supervisor, which is itself just an actor with a
-//! `Receiver<Signal>`. When a child actor terminates, the scheduler sends
-//! a `Signal` on the supervisor's channel. The supervisor decides what to
-//! do — restart, escalate, ignore.
+//! A *supervisor* is an actor whose only job is to start a fixed set of child
+//! actors and react when one of them terminates — restarting it (and, depending
+//! on the strategy, some of its siblings) according to a policy, or giving up
+//! when failures arrive too fast. It is how you turn "an actor that might crash"
+//! into "a service that stays up": a crash becomes a restart instead of a hole
+//! in the process tree.
 //!
-//! For v0.1 there is no built-in restart-intensity cap. That's policy and
-//! lives in user code; library is mechanism only.
+//! The supervisor type is [`OneForOne`]. The name is historical — the restart
+//! *strategy* is selectable via [`OneForOne::strategy`], and
+//! [`Strategy::OneForOne`] is merely the default. You declare the children up
+//! front as [`ChildSpec`]s, each carrying a [`Restart`] policy, then hand the
+//! supervision loop an actor of its own with [`OneForOne::run`].
+//!
+//! ## A child that crashes and recovers
+//!
+//! ```
+//! use smarm::{run, spawn, ChildSpec, OneForOne, Restart};
+//! use std::sync::Arc;
+//! use std::sync::atomic::{AtomicUsize, Ordering};
+//! use std::time::Duration;
+//!
+//! run(|| {
+//!     // A flaky child: it panics on its first two starts, then settles.
+//!     let starts = Arc::new(AtomicUsize::new(0));
+//!     let s = starts.clone();
+//!     let child = move || {
+//!         let n = s.fetch_add(1, Ordering::SeqCst) + 1;
+//!         if n < 3 {
+//!             panic!("boom {n}");
+//!         }
+//!         // The third start returns normally.
+//!     };
+//!
+//!     // The supervisor runs on its own actor. `Transient` restarts a child
+//!     // that panics but treats a clean return as "done", so once the child
+//!     // finally succeeds the supervisor has nothing left to do and `run()`
+//!     // returns. smarm catches the child's panic and turns it into a restart;
+//!     // it never reaches the process as a real crash.
+//!     let sup = spawn(move || {
+//!         OneForOne::new()
+//!             .intensity(5, Duration::from_secs(60))
+//!             .child(ChildSpec::new(Restart::Transient, child))
+//!             .run();
+//!     });
+//!     sup.join().unwrap();
+//!
+//!     assert_eq!(starts.load(Ordering::SeqCst), 3); // one start, two restarts
+//! });
+//! ```
+//!
+//! ## Restart policies
+//!
+//! Each child carries a [`Restart`] policy that decides whether *that child*
+//! comes back when it terminates:
+//!
+//!   - [`Restart::Permanent`] restarts on any termination, normal or panic —
+//!     for a service that should never be down.
+//!   - [`Restart::Transient`] restarts only on an abnormal exit (a panic or a
+//!     cooperative stop); a clean return means "done" — for work that runs to
+//!     completion but should be retried if it crashes.
+//!   - [`Restart::Temporary`] never restarts; the death is simply noted.
+//!
+//! ## Strategies: which siblings get cycled
+//!
+//! When a restart is due, the [`Strategy`] decides which *other* children are
+//! cycled along with the one that died. The triggering child's own policy still
+//! decides whether anything restarts at all.
+//!
+//!   - [`Strategy::OneForOne`] restarts only the child that died — the default.
+//!   - [`Strategy::OneForAll`] restarts every child: the survivors are stopped,
+//!     then the whole set is restarted.
+//!   - [`Strategy::RestForOne`] restarts the dead child and every child started
+//!     after it, leaving earlier children untouched.
+//!
+//! ## Stopping a sibling is cooperative
+//!
+//! Cycling a sibling means stopping it first, and a supervisor never tears a
+//! running actor down from outside: smarm actors share a heap and rely on
+//! Drop/RAII, so unwinding a peer's stack from elsewhere would be unsound.
+//! Instead the supervisor *requests* the stop and the child unwinds at its next
+//! observation point — a `check!()`, an allocation, or a blocking call. A child
+//! wedged in a tight loop with no observation point cannot be stopped, for the
+//! same reason it cannot be preempted.
+//!
+//! ## Giving up: the restart-intensity cap
+//!
+//! A child that crashes the instant it starts would otherwise restart forever.
+//! [`OneForOne::intensity`] bounds that: at most `max` restarts within any
+//! `period`-long sliding window. One terminating child counts as a single
+//! restart event even when the strategy cycles several siblings. When the cap
+//! trips, the supervisor stops restarting, cooperatively stops any survivors in
+//! reverse start order, and `run()` returns.
+//!
+//! ## Running context
+//!
+//! [`OneForOne::run`] takes over the calling actor as the supervision loop, so
+//! a supervisor gets an actor of its own — typically
+//! `spawn(|| OneForOne::new()/* … */.run())`, all from inside
+//! [`run`](crate::run). Each child is spawned beneath the supervisor's pid, so
+//! every child termination funnels back to it as a [`Signal`].
 
 use crate::pid::Pid;
 use std::any::Any;
 
+/// A child-termination notice delivered to its supervisor.
+///
+/// Every child a supervisor starts is spawned beneath the supervisor's pid, so
+/// each child's termination funnels back to it as one of these. The variant
+/// records *how* the child went — which is what its [`Restart`] policy keys off.
 pub enum Signal {
     /// The child exited normally.
     Exit(Pid),
@@ -42,27 +140,6 @@ impl Signal {
     }
 }
 
-// ---------------------------------------------------------------------------
-// One-for-one supervisor
-//
-// A supervisor is itself an actor. It spawns each child under its own pid so
-// that every child death funnels into one mailbox (the `supervisor_channel`),
-// then loops: receive a Signal, decide per the child's `Restart` policy
-// whether to restart, and enforce a restart-intensity cap so a child that
-// crashes in a tight loop eventually gives up instead of spinning forever.
-//
-// What this does NOT do: *forcibly* terminate a running child. smarm actors
-// share a heap and rely on Drop/RAII, so tearing down a peer's stack from
-// outside is unsound. Stopping a sibling — whether for `one_for_all` /
-// `rest_for_one`, for a propagated link death, or for the ordered shutdown
-// below — is therefore *cooperative*: `request_stop` flags the child and it
-// unwinds at its next observation point. A child with no observation points
-// (a tight loop with no `check!()`, allocation, or blocking op) cannot be
-// stopped, exactly as it cannot be preempted. When the intensity cap trips,
-// this supervisor stops restarting and tears the remaining children down in
-// reverse start order before returning.
-// ---------------------------------------------------------------------------
-
 use crate::channel::channel;
 use std::collections::{HashMap, VecDeque};
 use std::sync::Arc;
@@ -115,11 +192,10 @@ pub enum Strategy {
 
 /// A supervisor over a fixed set of children.
 ///
-/// Despite the name (kept for backwards compatibility), the restart strategy
-/// is selectable via [`OneForOne::strategy`]; the default is
-/// [`Strategy::OneForOne`]. Build with `new()`, add children with `child()`,
-/// tune the cap with `intensity()`, then drive it with `run()` from inside an
-/// actor (typically `spawn(|| OneForOne::new()....run())`).
+/// Build it with [`new`](Self::new), add children with [`child`](Self::child),
+/// pick a [`strategy`](Self::strategy) and an [`intensity`](Self::intensity)
+/// cap, then drive the loop with [`run`](Self::run) on an actor of its own. See
+/// the [module docs](self) for the full picture.
 pub struct OneForOne {
     children: Vec<ChildSpec>,
     strategy: Strategy,
@@ -253,7 +329,7 @@ impl OneForOne {
                     .collect(),
             };
             // Stop survivors in reverse start order (highest child index first).
-            to_stop.sort_unstable_by(|a, b| b.1.cmp(&a.1));
+            to_stop.sort_unstable_by_key(|x| std::cmp::Reverse(x.1));
 
             // The set we will restart: the failed child plus every sibling we
             // are about to stop, restarted in start (ascending index) order.
@@ -299,7 +375,7 @@ impl OneForOne {
         // and this is a no-op; on a cap-trip or mailbox-closed break it tears
         // the remaining children down deterministically instead of leaking them.
         let mut survivors: Vec<(Pid, usize)> = by_pid.iter().map(|(p, i)| (*p, *i)).collect();
-        survivors.sort_unstable_by(|a, b| b.1.cmp(&a.1));
+        survivors.sort_unstable_by_key(|x| std::cmp::Reverse(x.1));
         let mut awaiting: Vec<Pid> = Vec::with_capacity(survivors.len());
         for (pid, _) in &survivors {
             crate::scheduler::request_stop(*pid);

src/timer.rs

@@ -214,7 +214,10 @@ impl Timers {
         let mut out = Vec::new();
         while let Some(r) = self.heap.peek() {
             if r.0.deadline <= now {
-                let entry = self.heap.pop().unwrap().0;
+                let entry = match self.heap.pop() {
+                    Some(e) => e.0,
+                    None => panic!("smarm: timer heap pop after peek returned None (core corrupt)"),
+                };
                 if matches!(entry.reason, Reason::Send { .. }) && !self.armed.remove(&entry.seq) {
                     // Cancelled before it came due: discard, do not deliver.
                     continue;

src/trace.rs

@@ -101,7 +101,7 @@ mod inner {
 
     thread_local! {
         static LOCAL_STATE: std::cell::RefCell<Option<LocalState>> =
-            std::cell::RefCell::new(None);
+            const { std::cell::RefCell::new(None) };
     }
 
     // -----------------------------------------------------------------------
@@ -115,14 +115,20 @@ mod inner {
         let (tx, rx) = mpsc::channel::<Msg>();
         let start = Instant::now();
 
-        *GLOBAL.lock().unwrap() = Some(Global { sender: tx, start });
+        match GLOBAL.lock() {
+            Ok(mut g) => *g = Some(Global { sender: tx, start }),
+            Err(e) => panic!("smarm: trace lock poisoned (core corrupt): {e}"),
+        }
 
         // Drain thread: owns the Receiver, writes to disk.
         let path_for_thread = path.clone();
-        std::thread::Builder::new()
+        match std::thread::Builder::new()
             .name("smarm-trace-drain".into())
             .spawn(move || drain_thread(rx, &path_for_thread))
-            .expect("failed to spawn trace drain thread");
+        {
+            Ok(_) => {}
+            Err(e) => panic!("smarm: failed to spawn trace drain thread: {e}"),
+        }
 
         eprintln!("[smarm-trace] writing to {}", path);
     }
@@ -133,7 +139,10 @@ mod inner {
         // Drop the global sender so the drain thread's recv() returns Err
         // after the Flush sentinel, signalling clean shutdown.
         let sender = {
-            let mut g = GLOBAL.lock().unwrap();
+            let mut g = match GLOBAL.lock() {
+                Ok(g) => g,
+                Err(e) => panic!("smarm: trace lock poisoned (core corrupt): {e}"),
+            };
             g.take().map(|g| g.sender)
         };
         if let Some(tx) = sender {
@@ -162,7 +171,11 @@ mod inner {
             let mut opt = cell.borrow_mut();
             // Lazily initialise: one mutex hit per thread, ever.
             if opt.is_none() {
-                if let Some(g) = GLOBAL.lock().unwrap().as_ref() {
+                let guard = match GLOBAL.lock() {
+                    Ok(g) => g,
+                    Err(e) => panic!("smarm: trace lock poisoned (core corrupt): {e}"),
+                };
+                if let Some(g) = guard.as_ref() {
                     let tx = g.sender.clone();
                     *opt = Some(LocalState { tx, start: g.start });
                 }

tests/gen_statem.rs

@@ -1,76 +1,184 @@
 //! gen_statem behaviour tests, driven through the `gen_statem!` macro: cast/call
 //! round-trip, `enter` firing on start and on every real transition (but not on
-//! a stay), and the machine-down path when a handler panics.
+//! a stay), the machine-down path when a handler panics, and the timeout
+//! surface (state-timeout firing + auto-reset across transitions; named
+//! timeouts surviving transitions; cancellation).
 
 use smarm::gen_statem;
 use smarm::gen_statem::{CallError, Reply};
 use smarm::run;
 use std::sync::{Arc, Mutex};
+use std::time::Duration;
 
-// A two-state machine: Flip toggles, calls read counters, Boom panics.
+// ===========================================================================
+// Timeouts
+// ===========================================================================
+//
+// A small timer machine. `Idle` is quiet; `Armed` arms a state-timeout on entry
+// that — when it fires — bumps `st_fires` and returns to `Idle`. A named
+// timeout ("ping") is armed independently, survives the Idle/Armed transition,
+// and bumps `named_fires` when it fires. Counters are read back over calls.
+//
+// Durations are tiny and waits use `smarm::sleep` (parks the actor, leaves the
+// timer wheel turning). These tests run against real time, so they are a touch
+// slow; a controllable clock would tighten them.
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
-enum Switch {
-    Off,
-    On,
+enum T {
+    Idle,
+    Armed,
 }
 
-struct Counts {
-    flips: u32,
-    enters: u32,
+struct TData {
+    enters: u32,      // total state entries (incl. initial)
+    st_fires: u32,    // state-timeout fires
+    named_fires: u32, // named-timeout fires
+    st_window: u64,   // ms for the Armed state-timeout (set per test intent)
 }
 
-enum Cast {
-    Flip,
+enum TCast {
+    Arm,        // Idle -> Armed
+    Disarm,     // Armed -> Idle (a transition that should auto-reset the state-timeout)
+    Ping(u64),  // arm a named "ping" timeout after the given ms
+    CancelPing, // cancel the named "ping"
 }
 
-enum Call {
-    GetFlips(Reply<u32>),
-    GetEnters(Reply<u32>),
-    Boom(Reply<u32>),
+enum TCall {
+    Enters(Reply<u32>),
+    StFires(Reply<u32>),
+    NamedFires(Reply<u32>),
+    Boom(Reply<u32>), // panics, to exercise the call-to-dead-machine path
 }
 
 gen_statem! {
-    machine: Sm { state: Switch, data: Counts };
-    event:   Ev { cast: Cast, call: Call };
+    machine: TimerSm { state: T, data: TData };
+    event:   Ev2 { cast: TCast, call: TCall, info: () };
     context(data, prev, cx);
 
     enter {
-        _ => data.enters += 1,
+        // On entering Armed, arm the state-timeout. On Idle, nothing — and the
+        // loop has already auto-reset any pending state-timeout on the way in.
+        T::Armed => { data.enters += 1; cx.state_timeout(Duration::from_millis(data.st_window)); },
+        T::Idle  => data.enters += 1,
     }
 
-    on Switch::Off => {
-        cast Cast::Flip => { data.flips += 1; Switch::On },
-    }
-    on Switch::On => {
-        cast Cast::Flip => Switch::Off,
+    on T::Idle => {
+        cast TCast::Arm    => T::Armed,
+        cast TCast::Disarm => unhandled,
+        state_timeout      => unhandled,
     }
 
-    // State-independent queries: reply, then stay via `prev`. Boom panics
-    // (`boom()` is typed as a state tag so the arm stays well-formed).
+    on T::Armed => {
+        // The state-timeout elapsed while still Armed: count it and go Idle.
+        state_timeout      => { data.st_fires += 1; T::Idle },
+        cast TCast::Disarm => T::Idle,
+        cast TCast::Arm    => unhandled,
+    }
+
+    // State-independent rows: the named-timeout (survives transitions), the
+    // arm/cancel casts, the counter reads, and the panicking call.
     on _ => {
-        call Call::GetFlips(r)  => { r.reply(data.flips); prev },
-        call Call::GetEnters(r) => { r.reply(data.enters); prev },
-        call Call::Boom(_r)     => boom(),
+        cast TCast::Ping(ms)      => { cx.timeout("ping", Duration::from_millis(ms)); prev },
+        cast TCast::CancelPing    => { cx.cancel_timeout("ping"); prev },
+        timeout "ping"            => { data.named_fires += 1; prev },
+        timeout _                 => unhandled,
+        call TCall::Enters(r)     => { r.reply(data.enters); prev },
+        call TCall::StFires(r)    => { r.reply(data.st_fires); prev },
+        call TCall::NamedFires(r) => { r.reply(data.named_fires); prev },
+        call TCall::Boom(_r)      => boom(),
     }
 }
 
-fn boom() -> Switch {
+fn boom() -> T {
     panic!("boom")
 }
-// Casts are applied in order and a later call observes the accumulated data.
+
+// A state-timeout armed on entry to Armed fires after its window, bumping the
+// counter and returning the machine to Idle on its own.
+#[test]
+fn state_timeout_fires() {
+    let got = Arc::new(Mutex::new(0u32));
+    let got2 = got.clone();
+    run(move || {
+        let m = TimerSm::start(T::Idle, TData { enters: 0, st_fires: 0, named_fires: 0, st_window: 5 });
+        m.send(Ev2::Cast(TCast::Arm)).unwrap(); // -> Armed, arms 5ms state-timeout
+        smarm::sleep(Duration::from_millis(40)); // let it fire
+        *got2.lock().unwrap() = m.call(|r| Ev2::Call(TCall::StFires(r))).unwrap();
+    });
+    assert_eq!(*got.lock().unwrap(), 1, "state-timeout fired exactly once");
+}
+
+// Leaving Armed before the window elapses auto-resets the state-timeout: it
+// must not fire afterward, even though we wait well past its original window.
+#[test]
+fn state_timeout_auto_resets_on_transition() {
+    let got = Arc::new(Mutex::new(99u32));
+    let got2 = got.clone();
+    run(move || {
+        // Long window so the explicit Disarm beats it comfortably.
+        let m = TimerSm::start(T::Idle, TData { enters: 0, st_fires: 0, named_fires: 0, st_window: 50 });
+        m.send(Ev2::Cast(TCast::Arm)).unwrap(); // -> Armed, arms 50ms state-timeout
+        m.send(Ev2::Cast(TCast::Disarm)).unwrap(); // -> Idle, auto-resets it
+        smarm::sleep(Duration::from_millis(80)); // past the original window
+        *got2.lock().unwrap() = m.call(|r| Ev2::Call(TCall::StFires(r))).unwrap();
+    });
+    assert_eq!(*got.lock().unwrap(), 0, "auto-reset cancelled the pending state-timeout");
+}
+
+// A named timeout survives a state change: armed in Idle, it still fires after
+// the machine has moved to Armed and back.
+#[test]
+fn named_timeout_survives_transition() {
+    let got = Arc::new(Mutex::new(0u32));
+    let got2 = got.clone();
+    run(move || {
+        // Armed's own state-timeout is long so it doesn't interfere.
+        let m = TimerSm::start(T::Idle, TData { enters: 0, st_fires: 0, named_fires: 0, st_window: 200 });
+        m.send(Ev2::Cast(TCast::Ping(20))).unwrap(); // arm "ping" for 20ms (in Idle)
+        m.send(Ev2::Cast(TCast::Arm)).unwrap(); // -> Armed (ping must survive this)
+        m.send(Ev2::Cast(TCast::Disarm)).unwrap(); // -> Idle (and this)
+        smarm::sleep(Duration::from_millis(60)); // let "ping" fire
+        *got2.lock().unwrap() = m.call(|r| Ev2::Call(TCall::NamedFires(r))).unwrap();
+    });
+    assert_eq!(*got.lock().unwrap(), 1, "named timeout fired across the transitions");
+}
+
+// Cancelling a named timeout before its window prevents the fire.
+#[test]
+fn named_timeout_cancel() {
+    let got = Arc::new(Mutex::new(99u32));
+    let got2 = got.clone();
+    run(move || {
+        let m = TimerSm::start(T::Idle, TData { enters: 0, st_fires: 0, named_fires: 0, st_window: 200 });
+        m.send(Ev2::Cast(TCast::Ping(30))).unwrap(); // arm "ping" for 30ms
+        m.send(Ev2::Cast(TCast::CancelPing)).unwrap(); // cancel before it fires
+        smarm::sleep(Duration::from_millis(60)); // past the original window
+        *got2.lock().unwrap() = m.call(|r| Ev2::Call(TCall::NamedFires(r))).unwrap();
+    });
+    assert_eq!(*got.lock().unwrap(), 0, "cancel prevented the named-timeout fire");
+}
+
+// ===========================================================================
+// Core behaviour (cast/call round-trip, enter semantics, panic -> Down)
+// ===========================================================================
+
+// Casts are applied in order and a later call observes the resulting state via
+// its counters: two Arm/Disarm round-trips leave the machine back in Idle.
 #[test]
 fn cast_then_call_roundtrip() {
     let got = Arc::new(Mutex::new(0u32));
     let got2 = got.clone();
     run(move || {
-        let sw = Sm::start(Switch::Off, Counts { flips: 0, enters: 0 });
-        sw.send(Ev::Cast(Cast::Flip)).unwrap(); // Off -> On (flips = 1)
-        sw.send(Ev::Cast(Cast::Flip)).unwrap(); // On  -> Off (no flip count)
-        let flips = sw.call(|r| Ev::Call(Call::GetFlips(r))).unwrap();
-        *got2.lock().unwrap() = flips;
+        // Long state-timeout window so it never fires during the test.
+        let m = TimerSm::start(T::Idle, TData { enters: 0, st_fires: 0, named_fires: 0, st_window: 10_000 });
+        m.send(Ev2::Cast(TCast::Arm)).unwrap();    // Idle  -> Armed (enter)
+        m.send(Ev2::Cast(TCast::Disarm)).unwrap(); // Armed -> Idle  (enter)
+        m.send(Ev2::Cast(TCast::Arm)).unwrap();    // Idle  -> Armed (enter)
+        m.send(Ev2::Cast(TCast::Disarm)).unwrap(); // Armed -> Idle  (enter)
+        // enters = 1 (start) + 4 transitions = 5.
+        *got2.lock().unwrap() = m.call(|r| Ev2::Call(TCall::Enters(r))).unwrap();
     });
-    assert_eq!(*got.lock().unwrap(), 1, "turned On once across the two flips");
+    assert_eq!(*got.lock().unwrap(), 5, "one enter on start, one per real transition");
 }
 
 // `enter` fires once on start and once per *real* transition; a stay (a call
@@ -80,14 +188,14 @@ fn enter_on_start_and_each_transition_but_not_stay() {
     let got = Arc::new(Mutex::new((0u32, 0u32, 0u32)));
     let got2 = got.clone();
     run(move || {
-        let sw = Sm::start(Switch::Off, Counts { flips: 0, enters: 0 }); // enter -> 1
-        let after_start = sw.call(|r| Ev::Call(Call::GetEnters(r))).unwrap();
-        // Two stays (the reads) must not bump enters.
-        let _ = sw.call(|r| Ev::Call(Call::GetFlips(r))).unwrap();
-        let still = sw.call(|r| Ev::Call(Call::GetEnters(r))).unwrap();
-        sw.send(Ev::Cast(Cast::Flip)).unwrap(); // Off -> On -> enter -> 2
-        let after_flip = sw.call(|r| Ev::Call(Call::GetEnters(r))).unwrap();
-        *got2.lock().unwrap() = (after_start, still, after_flip);
+        let m = TimerSm::start(T::Idle, TData { enters: 0, st_fires: 0, named_fires: 0, st_window: 10_000 }); // enter -> 1
+        let after_start = m.call(|r| Ev2::Call(TCall::Enters(r))).unwrap();
+        // A stay (a counter read returns `prev`) must not bump enters.
+        let _ = m.call(|r| Ev2::Call(TCall::StFires(r))).unwrap();
+        let still = m.call(|r| Ev2::Call(TCall::Enters(r))).unwrap();
+        m.send(Ev2::Cast(TCast::Arm)).unwrap(); // Idle -> Armed -> enter -> 2
+        let after_arm = m.call(|r| Ev2::Call(TCall::Enters(r))).unwrap();
+        *got2.lock().unwrap() = (after_start, still, after_arm);
     });
     assert_eq!(*got.lock().unwrap(), (1, 1, 2));
 }
@@ -100,9 +208,173 @@ fn call_to_panicking_handler_is_down() {
     let got = Arc::new(Mutex::new(None::<Result<u32, CallError>>));
     let got2 = got.clone();
     run(move || {
-        let sw = Sm::start(Switch::Off, Counts { flips: 0, enters: 0 });
-        let r = sw.call(|rep| Ev::Call(Call::Boom(rep)));
+        let m = TimerSm::start(T::Idle, TData { enters: 0, st_fires: 0, named_fires: 0, st_window: 10_000 });
+        let r = m.call(|rep| Ev2::Call(TCall::Boom(rep)));
         *got2.lock().unwrap() = Some(r);
     });
     assert_eq!(*got.lock().unwrap(), Some(Err(CallError::Down)));
 }
+
+// ===========================================================================
+// Postpone
+// ===========================================================================
+//
+// Two machines. `LatchSm` defers a `Take` *call* while `Empty` and answers it
+// from `Filled` — the Reply rides inside the postponed event onto the queue and
+// is honoured by whichever later state handles the replay. `RelaySm` defers a
+// `Mark` cast through two states so a replayed event can postpone *again*,
+// landing only once the handling state is reached.
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+enum L {
+    Empty,
+    Filled,
+}
+
+struct LData {
+    value: u32, // the value a Fill stored, handed back by a Take
+    takes: u32, // completed takes
+}
+
+enum LCast {
+    Fill(u32), // Empty -> Filled, storing the value
+}
+
+enum LCall {
+    Take(Reply<u32>),  // Filled: reply value & empty; Empty: postpone until filled
+    Takes(Reply<u32>), // completed-take count (stay)
+    Status(Reply<L>),  // current state tag (stay)
+}
+
+gen_statem! {
+    machine: LatchSm { state: L, data: LData };
+    event:   LEv { cast: LCast, call: LCall, info: () };
+    context(data, prev, cx);
+
+    enter { _ => {} }
+
+    on L::Empty => {
+        cast LCast::Fill(v) => { data.value = v; L::Filled },
+        // No value yet: defer the take (with its Reply) until a Fill arrives.
+        call LCall::Take(r)  => postpone,
+    }
+    on L::Filled => {
+        cast LCast::Fill(_) => unhandled, // already full
+        call LCall::Take(r)  => { r.reply(data.value); data.takes += 1; L::Empty },
+    }
+    on _ => {
+        call LCall::Takes(r)  => { r.reply(data.takes); prev },
+        call LCall::Status(r) => { r.reply(prev); prev },
+        state_timeout => unhandled,
+        timeout _     => unhandled,
+    }
+}
+
+// A `Take` issued while the latch is Empty parks the caller and is postponed
+// (Reply included). A later Fill transitions Empty -> Filled, whose replay
+// answers the deferred call — the parked caller wakes with the filled value.
+#[test]
+fn postponed_call_answered_after_transition() {
+    let got = Arc::new(Mutex::new(None::<u32>));
+    let g2 = got.clone();
+    run(move || {
+        let m = LatchSm::start(L::Empty, LData { value: 0, takes: 0 });
+
+        // Child actor issues the Take while Empty; its call parks on the reply.
+        let m2 = m.clone();
+        let taken = Arc::new(Mutex::new(None::<u32>));
+        let t2 = taken.clone();
+        smarm::scheduler::spawn(move || {
+            let v = m2.call(|r| LEv::Call(LCall::Take(r))).unwrap();
+            *t2.lock().unwrap() = Some(v);
+        });
+        smarm::sleep(Duration::from_millis(20)); // let the Take land and be deferred
+
+        // While deferred, the latch is untouched: still Empty, no take completed.
+        // (These reads are stays — they don't disturb the postponed event.)
+        assert_eq!(m.call(|r| LEv::Call(LCall::Status(r))).unwrap(), L::Empty);
+        assert_eq!(m.call(|r| LEv::Call(LCall::Takes(r))).unwrap(), 0);
+
+        m.send(LEv::Cast(LCast::Fill(42))).unwrap(); // Empty -> Filled: replays the Take
+        smarm::sleep(Duration::from_millis(20)); // let the child wake with its reply
+        *g2.lock().unwrap() = *taken.lock().unwrap();
+    });
+    assert_eq!(*got.lock().unwrap(), Some(42), "postponed call answered by the Filled state");
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+enum R {
+    S0,
+    S1,
+    S2,
+}
+
+struct RData {
+    marks: u32, // Marks handled (only S2 handles one)
+}
+
+enum RCast {
+    Go,   // S0 -> S1 -> S2 -> S0
+    Mark, // postponed in S0/S1, handled in S2
+}
+
+enum RCall {
+    Marks(Reply<u32>),
+    State(Reply<R>),
+}
+
+gen_statem! {
+    machine: RelaySm { state: R, data: RData };
+    event:   REv { cast: RCast, call: RCall, info: () };
+    context(data, prev, cx);
+
+    enter { _ => {} }
+
+    on R::S0 => {
+        cast RCast::Go   => R::S1,
+        cast RCast::Mark => postpone,
+    }
+    on R::S1 => {
+        cast RCast::Go   => R::S2,
+        cast RCast::Mark => postpone, // a replay here defers again
+    }
+    on R::S2 => {
+        cast RCast::Go   => R::S0,
+        cast RCast::Mark => { data.marks += 1; prev }, // finally handled
+    }
+    on _ => {
+        call RCall::Marks(r) => { r.reply(data.marks); prev },
+        call RCall::State(r) => { r.reply(prev); prev },
+        state_timeout => unhandled,
+        timeout _     => unhandled,
+    }
+}
+
+// A postponed event that is replayed into a state which *also* postpones it
+// re-queues, and is handled only once a state that accepts it is reached. Each
+// `Marks` call is a stay that acts as a sync barrier after the preceding casts.
+#[test]
+fn replayed_event_can_postpone_again() {
+    let got = Arc::new(Mutex::new((9u32, 9u32, 9u32, R::S0)));
+    let g2 = got.clone();
+    run(move || {
+        let m = RelaySm::start(R::S0, RData { marks: 0 });
+
+        m.send(REv::Cast(RCast::Mark)).unwrap(); // S0: postponed
+        let a = m.call(|r| REv::Call(RCall::Marks(r))).unwrap(); // deferred -> 0
+
+        m.send(REv::Cast(RCast::Go)).unwrap(); // S0 -> S1: replay Mark -> postponed again
+        let b = m.call(|r| REv::Call(RCall::Marks(r))).unwrap(); // re-deferred -> 0
+
+        m.send(REv::Cast(RCast::Go)).unwrap(); // S1 -> S2: replay Mark -> handled
+        let c = m.call(|r| REv::Call(RCall::Marks(r))).unwrap(); // -> 1
+        let s = m.call(|r| REv::Call(RCall::State(r))).unwrap(); // Mark was a stay in S2
+
+        *g2.lock().unwrap() = (a, b, c, s);
+    });
+    let (a, b, c, s) = *got.lock().unwrap();
+    assert_eq!(a, 0, "deferred while S0");
+    assert_eq!(b, 0, "re-deferred while S1");
+    assert_eq!(c, 1, "handled once S2 is reached");
+    assert_eq!(s, R::S2, "Mark handled as a stay in S2");
+}