v0.6: state.stack, until(loc), finish(), prelude show.* helpers

- StackRegion from /proc/<pid>/maps, exposed as state.stack
  ({top, usable_base, guard_size} BigInts per spec)
- until(loc) one-shot bp wrapper that cleans up via try/finally,
  works even if a different stop fires first
- finish() reads return address from [rbp+8] and uses until()
- updated js.rs module doc; allow(dead_code) on the kept-for-future
  BreakpointSet::find_by_name

src/js.rs

@@ -1,15 +1,22 @@
 //! QuickJS REPL: persistent context, ptrace target lives behind an Rc<RefCell>,
 //! globals are installed once at construction.
 //!
-//! v0.1 surface:
-//!   spawn(path, ...args) -> { pid, status }
-//!   step(n=1)            -> stop-reason string
-//!   continue()           -> stop-reason string  (exposed as `continue` and `cont`)
-//!   print(...args)       -> writes to stdout
-//!   ctx                  -> persistent plain object
-//!   state.pc / .sp       -> BigInt
-//!   state.registers      -> object of BigInts
-//!   state.memory(addr)   -> { u8(), u32(), u64(), i64(), bytes(n) }
+//! Native globals installed here:
+//!   spawn(path, ...args)                       -> { pid, status }
+//!   step(n=1) / cont()                         -> stop-reason string
+//!   print(...args), ctx (persistent object)
+//!   state.pc, state.sp                         -> BigInt (live ptrace)
+//!   state.registers                            -> object of BigInts
+//!   state.memory(addr) -> { u8/u32/u64/i64/bytes }
+//!   state.disasm(n=8)                          -> [{addr, bytes, text, target?, target_sym?}]
+//!   state.stack                                -> { top, usable_base, guard_size }
+//!   prev                                       -> register snapshot from before last resume
+//!   sym(addr), addr(name), symbols()
+//!   disasm(addr, n=8)
+//!   breakpoint / bp: .set, .remove, .list
+//!
+//! JS-side helpers (in prelude.js): hex, unhex, dump, repr, addrstr, here,
+//! until, finish, show.{disasm,bp,regs}.
 
 use crate::target::Target;
 use rquickjs::function::Rest;
@@ -314,6 +321,24 @@ fn install_globals<'js>(
             state_obj.set("disasm", f)?;
         }
 
+        // state.stack — accessor returning {top, usable_base, guard_size} as BigInts
+        {
+            let target = target.clone();
+            state_obj.prop(
+                "stack",
+                Accessor::from(move |c: Ctx<'js>| -> rquickjs::Result<Value<'js>> {
+                    let slot = target.borrow();
+                    let t = slot.as_ref().ok_or_else(|| throw(&c, "no target attached"))?;
+                    let s = t.stack().ok_or_else(|| throw(&c, "no stack info"))?;
+                    let obj = Object::new(c.clone())?;
+                    obj.set("top", u64_to_bigint(&c, s.high)?)?;
+                    obj.set("usable_base", u64_to_bigint(&c, s.low)?)?;
+                    obj.set("guard_size", u64_to_bigint(&c, s.guard_size)?)?;
+                    Ok(obj.into_value())
+                }),
+            )?;
+        }
+
         globals.set("state", state_obj)?;
     }