#43: CM-4 filing kit — schedule-agnostic sync-streams patch + ready-to-file issue draft

[lann]

What

The remaining deliverable of #43 (the runtime migration landed in #45; the adjudication re-scoped the issue to the filing kit): ready-to-file upstream artifacts for the CM-4 test-defect finding.

• upstream-issue-sync-streams-schedule-overfit.md — issue draft against WebAssembly/component-model, following the upstream-issue-stale-async-drop.md convention. Body distills the final adjudication (issue CM-4: sync-streams.wast:145 overfits wasmtime's scheduler — upstream test-defect filing kit #43, 2026-08-10): gate semantics are agreed by definitions.py, wasmtime, and the CanonicalABI.md prose; what sync-streams.wast:145 hard-asserts is the entry-decision timing, a non-normative scheduler policy on which the reference (eager-inline → STARTING) and wasmtime (deferred → STARTED) conformingly disagree.
• upstream-sync-streams-schedule-agnostic.patch — the proposed test fix, git apply --check-verified against spec HEAD 73b7ad5: accept STARTING|STARTED from the lower; on STARTING, wait for the subtask's admission (STARTED) before touching the stream; every other assertion unchanged. The STARTED arm is byte-identical to today's assertions, so the current runner (wasmtime) loses no coverage.
• Tracker CM-4 entry updated to kit-READY; filing remains operator-gated via File the upstream findings (IROH-1; component-model tracker) #15.

Every definitions.py/CanonicalABI.md/wast line citation in the draft was re-verified against the 73b7ad5 submodule pin.

Closes #43.

Verification

Pipeline: scratch test-dir → testgen --test-dir X --out-dir Y async → runWastJson with RuntimeExecutor (real shim), no xfail filtering.

leg	arm exercised	FIFO	seed 1	seed 4242
pristine sync-streams.wast (control)	STARTED	2/2	—	—
patched sync-streams.wast	STARTED (else-arm)	2/2	2/2	2/2
STARTING-variant (below)	STARTING (hard-asserted)	2/2	2/2	2/2

The STARTING arm is dead code under deltic's drain-to-quiescence policy in the patched scenario (deltic answers STARTED, like wasmtime). To execute the new arm on a live engine rather than argue it by inspection, the variant leg reorders $D.run so $C.set is called before the stream-1 read: $C.get's mid-frame park is then unready, no amount of draining can admit the callee, and the call reports STARTING (the semantics pinned by runtime/tests/entry_deferral_test.ts). The variant hard-asserts STARTING at the call, performs the stream-1 read/drop to make the holder ready, then runs the patched STARTING arm verbatim (wait for SUBTASK/STARTED with payload asserts) and the unchanged tail. Its 2/2 pass under FIFO + both seeds means the proposed arm's waits and asserts executed and held.

Reproduction recipe

# worktree at this PR's commit; shim + testgen built:
cargo build -p translator-shim --target wasm32-unknown-unknown --release
cargo build -p testgen

mkdir -p /tmp/cm4/{pristine,patched}/test/async
cp third_party/component-model/test/async/sync-streams.wast /tmp/cm4/pristine/test/async/
cp third_party/component-model/test/async/sync-streams.wast /tmp/cm4/patched/test/async/
(cd /tmp/cm4/patched && git apply $OLDPWD/upstream-sync-streams-schedule-agnostic.patch)

for t in pristine patched; do
  cargo run -q -p testgen -- --test-dir /tmp/cm4/$t/test --out-dir /tmp/cm4/$t/generated async
done
# run each generated async/sync-streams.json through harness/src/runner.ts
# runWastJson + RuntimeExecutor.create(shim), asserting zero failures; rerun
# with DELTIC_SCHED_SEED=1 and =4242. (Scratch driver: ~25 lines importing
# @deltic-workspace harness modules; must run from inside the workspace so
# the @deltic/* workspace specifiers resolve.)

Variant construction: apply the kit patch, then in $D.run (1) add (local $rx2 i32), (2) move the stream-1 read/assert/drop block to after the $C.set call + waitable-set.new/join, calling $set with $rx2 from the stream.new pair, (3) replace the two-arm if with a hard (if (i32.ne (i32.const 0 (; STARTING ;)) ...) (then unreachable)) followed by the STARTING arm's wait/asserts inline, (4) leave the tail unchanged. Header comment in the variant marks it deltic-verification-only (not for upstream).

Filing boundary

Nothing is filed upstream by this PR; the draft + patch are artifacts for the operator (#15). The wasmtime-dev leg (wasmtime wast -W component-model-async=y -W component-model-more-async-builtins=y test/async/sync-streams.wast) is documented in the filing notes as an optional pre-filing courtesy — by construction the patch only adds an arm wasmtime never takes.