enter-sync-call: sibling reentrance cycle (A -> C -> A) is untrapped — reference mandates trap; needs corpus/wasmtime differential

[lann]

Severity: medium (conformance), adjudication required before code.

enter-sync-call (intrinsics/mod.ts:454-483) performs no may_enter
check. In the reference, every guest->guest call routes through the callee
lift's enter gate (definitions.py:581 chain), so a sync fused-adapter
cycle A -> C -> A traps "cannot enter component instance". FACT's static
trap covers only same/ancestor pairs (trusted fact/trampoline.rs:124), and
the trusted wasmtime sources examined (concurrent.rs:1723) show no obvious
sibling-cycle rejection either — this may be wasmtime parity or a shared
gap.

Protocol (docs/architecture.md §1): bare wasmtime behavior never
supersedes the reference; a corpus assertion counts only if
schedule-independent. So:

1. Check the official suite + wasmtime misc corpus for sibling-cycle
   coverage (async/ and linking/ wast files). If a schedule-independent
   corpus test pins the permissive behavior, stop and re-adjudicate
   (CM-3-style exception, named finding).
2. Build the differential fixture (3-component composition, A -> C -> A
   through sync fused adapters) and run it under native wasmtime
   (installed CLI, 47.x) and deltic.
3. Absent corpus backing for permissiveness: implement the reference trap
   in enter-sync-call (may_enter check against the callee instance,
   same-instance/ancestor semantics per the reference chain), and record
   any wasmtime delta in upstream-component-model-repo-findings.md
   (tracker entry; filing is the operator's call).

Found in the 2026-08-10 adversarial conformance review (runtime + translator vs component-model @ 73b7ad5 definitions.py; wasmtime-environ 47.0.3 treated as trusted).

[lann]

Adjudication landed with PR #103 (commit 68dc4cf): reference gate implemented at enter-sync-call; sibling cycle unreachable by construction (instance-import DAG — wasm-tools rejects the mutual-import composition; wasmtime elides the runtime check on the same ground, concurrent.rs:1876-1886). No wasmtime/reference delta to record. The reachable residue (host-entry gate locks only the leaf because the instance parent chain has no wire form) is #101; the FACT exit-before-result-translation timing note from the same investigation is recorded in #101's body.

[lann]

Fixed by PR #103 (merged; commits 058894f/9a6bb9c/3500ab4/68dc4cf/26d6016/c855b33 per issue group — GitHub didn't link the full comma-separated Fixes list).