pin-advance migration map: CM#705 removes the may_enter flag/trap

[lannbot]

Upstream is removing the non-reentrancy restriction: WebAssembly/component-model#705 ("CABI: remove the may_enter flag/trap", open as of 2026-08-20) deletes the may_enter flag+trap from the canon lift, resource.drop (destructor), and subtask.cancel paths and from cooperative scheduling conditions, making previously-trapping reentrance valid (new WAST coverage: reentrance.wast, the during-sync-call-* family, rewritten trap-on-reenter.wast). What remains upstream is "run to completion": exclusive-thread serialization of async callback turns via automatic backpressure. (#696/#697 are obviated by it.)

Discipline: the pinned definitions.py stays the tie-breaker until the submodule pin is deliberately advanced (docs/architecture.md §1). Nothing is removed preemptively. This issue is the map, filed so (a) no further investment lands in machinery with an expiry date, and (b) the pin-advance PR has a plan waiting.

Inventory: deltic machinery keyed on may_enter, with dispositions

1. Synthetic per-instantiation root (plan v3 amendment 4 / plan/task: component instance tree has no wire form — host-entry reentrance gate locks only the leaf #101: ComponentInstanceState.rootOf, isSyntheticRoot, enteringSet's host-entry {leaf, root}) — exists solely so host-entry reentrance traps through entering_set(None). Delete. The plan format never carried a wire form for the tree, so this is a contract-text amendment (orchestrator event), not a wire change.
2. The enter/leave bracket discipline at every site: createLiftedFunction's host-entry gate, Store.tick's bracket, Thread.resumeWith's bracket, Task.requestCancellation's delivery gate+bracket (#705 removes the subtask.cancel check outright — note task core: record tick's poison marker; keep the bracket broken on cancellation-delivery traps #164's fix there is on the removal list), the FACT start-call gates (fact_calls.ts), enter-sync-call's check (adjudicated reentrance: enter-sync-call checks the callee gate but never takes it — host-mediated reentry passes where the reference traps #165), and the dtor lift's entry gate. Reentrance enforcement goes; only poisoning refusal remains (next item). The lift harness itself (resources: host-initiated dtors run as full canonical lifts #163) stays — it is canon_resource_drop's model independent of the gate.
3. Poisoning re-keys onto the marker. Per-instance poisoning (deltic's named divergence from store-fatal traps) is currently implemented as "mayEnter stays false forever" with the poisonedInstances WeakMap as a shadow (Go components trap (and poison their instance) when the Go runtime reads the clock inside cabi_realloc #145). Post-#705 the WeakMap marker is the only mechanism: entry refusal = isInstancePoisoned + withPoisonCause; releaseSyntheticRootOnPoison deleted. Prerequisite — every bracket-break site must record the marker — landed in task core: record tick's poison marker; keep the bracket broken on cancellation-delivery traps #164 (the tick-path gap).
4. The scheduler: tick skips threads whose instance is not host-enterable #155 tick filter and scheduler: resumeWith has the same not-host-enterable window as tick, and the tick fix cannot transfer #156/scheduler: settled tails defer while their instance is not host-enterable #161 deferral machinery (readyCandidates enterability filter, dispatchableTail, hasServiceableSettled, serviceSettled skip-in-place, driveAsync's race-set exclusion and all-deferred fallthrough). The lock states they defend against cease to exist; what survives is poisoned-tail retirement (resumeWith's early return). Most of scheduler: settled tails defer while their instance is not host-enterable #161 becomes removable — revisit whether the race-set exclusion is still load-bearing once nothing can defer (a queued settled entry is then always immediately serviceable).
5. Trap-message surface: the transient "cannot enter component instance (reentrance forbidden)" disappears; the poisoned-corpse refusal (with the Go components trap (and poison their instance) when the Go runtime reads the clock inside cabi_realloc #145 cause suffix) remains. Check corpus wording expectations.
6. Unaffected: backpressure/exclusive-thread and the CM-4: sync-streams.wast:145 overfits wasmtime's scheduler — upstream test-defect filing kit #43 deferred-entry policy (run-to-completion is retained upstream); the settlement/host-activity driver architecture; embedder/streams: a lifted wrapper's HostActivity arm outlives the hand-back to the guest — one identity round-trip suppresses deadlock verdicts forever #162 (arm liveness), streams: teardown abandon of a parked-write future discards a delivered value; reader poisoned for the writer's fault #168 (future teardown), embedder boundary: missing record/flags labels lower silently; multi-store lift failures escape as AssertionError #170 (embedder fault discipline) — orthogonal.
7. Tests: the task_test.ts synthetic-root section (plan/task: component instance tree has no wire form — host-entry reentrance gate locks only the leaf #101/scheduler: tick skips threads whose instance is not host-enterable #155/scheduler: resumeWith has the same not-host-enterable window as tick, and the tick fix cannot transfer #156/task core: record tick's poison marker; keep the bracket broken on cancellation-delivery traps #164 pins), settled_deferral_test.ts, and dtor_normalization_test.ts's sibling-enterability pin mostly invert or become obsolete; the poisoning pins survive re-keyed per item 3. The conformance corpus gains #705's new reentrance family and loses trap expectations — testgen regen + expectation triage, including per-browser overlays.

Sequencing sketch

1. Wait for upstream merge (the PR may still change — re-derive this map against the merged form).
2. Pin advance in its own PR: submodule bump + testgen regen + corpus triage, no runtime changes beyond what the corpus forces.
3. Mechanical removal tracks, poisoning re-key (item 3) FIRST, then filters/deferral (item 4), then the root (item 1, with the contract amendment).
4. Close reentrance: enter-sync-call checks the callee gate but never takes it — host-mediated reentry passes where the reference traps #165's named-divergence entry in docs/architecture.md as resolved.