roadmap: ship v0.9, promote Process groups to up-next

- Compact v0.9 (Wake-path latency) into Shipped; record the RFC 004 spinning
  excision as a deviation (preserved on branch rfc-004-spinning).
- Drop the v0.7 entry, folding its reference into the Shipped history pointer.
- Promote Process groups from Later into the up-next slot v0.9 vacated;
  Per-switch cost now leads Later/Highest priority.

ROADMAP.md

@@ -2,20 +2,9 @@
 
 ## Shipped (compacted — full cycle plans and deviation records live in git history)
 
-Cycles before v0.7 (v0.4 actor primitives, v0.5 runtime decomposition &
-pluggable run queue, v0.6 actor ergonomics): see `git log ROADMAP.md`.
-
-### v0.7 — select, on epoch-stamped consuming wakes  ✅
-A 24-bit park-epoch packed into the slot word gives every wait an identity:
-registrations carry `(pid, epoch)`, every successful wake **consumes** the
-epoch, stale wakes die at one failed CAS. Subsumed the per-primitive wait
-seqs (channel, mutex, timer); the only wildcard wake left is `request_stop`
-(terminal). On top: `select`/`select_timeout` — ready-index wait over many
-receivers, priority order, no cancellation pass. Loom theorems re-proved on
-the new word. Notable deviations: `retire_wait` for the no-park exit path
-(plan missed it); the Drop-guard deregistration was superseded by relaxed
-single-receiver asserts; a closed arm is ready *forever* (documented gotcha).
-Commits `4913835`…`00128f3`, `a0a93b6`.
+Cycles before v0.8 (v0.4 actor primitives, v0.5 runtime decomposition &
+pluggable run queue, v0.6 actor ergonomics, v0.7 select on epoch-stamped
+consuming wakes): see `git log ROADMAP.md`.
 
 ### v0.8 — gen_server: handle_info / handle_down + io fd hygiene  ✅
 Spent `select` on the server loop: static info arms (`type Info`,
@@ -27,6 +16,19 @@ entry permanently poisoned the fd). Deviation: the plain-inbox fast path
 narrowed; servers holding a `Watcher` select forever.
 Commits `e5d1b3b`, `24b95c9`, `f6969e5`.
 
+### v0.9 — Wake-path latency  ✅
+Attacked per-wake latency with the RFC 005 **wake slot**: a per-scheduler,
+thread-local, capacity-one wake cache checked before the shared queue, pushed
+only from actor context, slot-then-shared pop with the waker's residual slice
+as the starvation bound (`slot_hits`/`slot_displacements`). Benched via the
+slot on/off dimension of `rq_runtime` — ping-pong-pairs (win), yield-storm
+(regression guard), spawn-storm (neutrality); results annotated in RFC 005.
+The RFC 004 spinning-workers experiment, originally scoped here, was evaluated
+and **excised** (not worth the code cost; preserved on branch
+`rfc-004-spinning`). Also a false-sharing fix (`align(64)` on `SchedulerStats`)
+and a termination wake for idle siblings.
+Commits `2708042`, `37d9319`, `eddf3fe`.
+
 ---
 
 ## Decision record — queue topology  🔒 CLOSED (2026-06-10)
@@ -48,51 +50,7 @@ Consequences:
 
 ---
 
-## v0.9 — Wake-path latency
-
-Goal: attack per-wake latency — the measured ceiling — with the two specified
-mechanisms, each benched against a clean baseline before the next lands.
-Order: RFC 005 first (the slot is measured against the just-benched idle
-policy), then RFC 004 (measured against the slot-accepted baseline), then an
-interaction pass.
-
-Full specs: `rfc_005-wake-slot.md`, `rfc_004-tunable-scheduler-idle-policy.md`
-(artefacts.kalsbeek.dev).
-
-### 1. Wake slot (RFC 005)
-Per-scheduler, thread-local, capacity-one wake cache, checked before the
-shared queue. Runtime-selected via `Config { wake_slot: bool }`, default off
-until accepted (one binary benches both arms).
-- **Push policy:** slot-eligible iff the wake originates from actor context
-  (`current_pid().is_some()`). Scheduler-context wakes (timer/IO drain) and
-  spawns always go shared.
-- **Displacement:** newest wake takes the slot, occupant pushed shared (Go
-  semantics); the branch swap is the fallback if benches look pathological.
-- **Pop order:** slot, then shared. Slot-popped actors inherit the waker's
-  remaining timeslice — a handoff chain is bounded by one slice, so the
-  shared queue is consulted at least once per slice per scheduler (the
-  starvation bound, zero new counters).
-- **Invariant care:** the slot push replaces `run_queue.push` at the tail of
-  the `Parked → Queued` CAS; at-most-once-enqueued holds verbatim (pid in
-  slot ⊕ shared queue). Stall blast radius grows by exactly one actor.
-- Counters: `slot_hits`, `slot_displacements`.
-
-### 2. Slot shootout
-Extend `rq_runtime`/`bench_rq.sh` with the slot on/off dimension (cheap —
-it's a Config knob, not a feature rebuild). Same sweep as the rq shootout.
-- **ping-pong-pairs** — target metric; expect the win, single- and
-  multi-scheduler.
-- **yield-storm** — regression guard; yields never touch the slot, any delta
-  is pop-path overhead.
-- **spawn-storm** — neutrality check; spawns bypass the slot by policy.
-Acceptance flips the default on and re-baselines for RFC 004.
-This is done, see results annotated in RFC005.
-
----
-
-## Later
-### Highest priority
-#### Process groups: the primitive pubsub & channels should have sat on
+## Up next — Process groups: the primitive pubsub & channels should have sat on
 Context: urus is a webserver written on top of smarm to provide a testing target.
 A named pid→multiset map with monitor-backed removal: `registry.rs` generalised
 from name↔pid *bimap* to name→*multiset*, the death hook reused verbatim. Local
@@ -103,6 +61,10 @@ member), with different netsplit consequences. Urus shipped pubsub/channels pred
 and want reframing on top of it. Foundational, so early in the post-v0.9 stack.
 Needs an RFC.
 
+---
+
+## Later
+### Highest priority
 #### Per-switch cost (context shims, epoch protocol)
 The shootout's residual: per-wake latency is 0.16–0.18 µs at N=1 and
 0.8–1.2 µs at N=8+, dominated by the context-switch shims and the epoch