forth: JIT cooperation hooks (vm-eligible flag + call-count + forth-hot-words)

plans/forth-on-sx.md

@@ -100,12 +100,24 @@ Representation:
 ### Phase 6 — speed
 - [x] Inline primitive calls during compile (skip dict lookup)
 - [x] Tail-call optimise colon-def endings
-- [ ] JIT cooperation: mark compiled colon-defs as VM-eligible
+- [x] JIT cooperation: mark compiled colon-defs as VM-eligible
 
 ## Progress log
 
 _Newest first._
 
+- **Phase 6 close — JIT cooperation hooks (Hayes unchanged at 618/638).**
+  Every word record now carries `:vm-eligible? true` and a
+  `:call-count` counter that `forth-execute-word` bumps on every
+  invocation. The flag is a hint for downstream JIT consumers — our
+  bodies are plain SX lambdas already, so the existing SX VM's
+  on-first-call JIT lifts them into bytecode automatically; the
+  metadata just makes that fact discoverable. Added
+  `forth-hot-words state threshold` returning `(name count)`
+  pairs above a threshold so a future tracing JIT can pick out
+  hot definitions to specialise. Phase 6 boxes all ticked.
+  All 306 internal tests green; Hayes Core stays at 618/638.
+
 - **Phase 6 — TCO at colon-def endings (Hayes unchanged at 618/638).**
   `forth-run-body` now special-cases the final op when it's a plain
   function (not a branch dict): we call it in tail position with no