Opt-in head yield observer — 2026-10-24

Implementation passes cheap controls. Native off/on equivalence is NOT qualified. The only authorized retained-module attempt failed an off-control fixture assertion before the on lane ran. No repeat, game, build, acquisition, box or deployment. Historical original-game zero-record cause, EDI target and errno remain UNKNOWN.

tools/maelstrom-head-yield-observer.cjs transforms only the historical runner SHA-256 4d7b9587676db38fcf3314807acb2b2a42b5f09d2c98fcf3dccb8a6cde9e1809, with pinned export source 739397dc54a77e93b367334fd4ca96c921180f57a7558913a3301f1de4520b86 at revision d8cd8c54c8d63c107696f1e4ef7a1e229dcadc1e. Disabled transform returns the input byte for byte. Enabled mode requires exact, unique anchors and both pins. Raw watch flags are rejected during argument parsing, before guest memory exists, including deferred/JS-only watch configurations.

The explicit profile is --trace-at=7a3362 --trace-at-start-batch=36163 --trace-at-limit=1 --count=7a3362,7a3366, original batch size 1000, no break or watch configuration. Use the historical runner's normal startup recipe; this profile does not itself supply game inputs or authorize a guest. CLI:

node tools/maelstrom-head-yield-observer.cjs --enable PINNED_RUN_JS PINNED_EXPORTS_WAT NEW_ADJACENT_RUN_JS

The new output must be adjacent to the runner for its relative imports. No extra run, breakpoint write, counter clear, clock change or guest-memory write is added. The existing set_bp is observed, and the existing main run/skip conditional is wrapped without changing its scheduling decision. A genuine head halt requires halt 5, matching EIP/breakpoint readback and exact instruction bytes 8b e8 ff d7 83 38 04. Registers EDI/EAX/EBP/ESP, yield reason/flag, halt, entry counters, cache stores/clears/invals and block count are read through real export names from pinned src/13-exports.wat. Six boundary pairs, arm and summary produce at most 14 records, with enforced ceilings of 16 records/8192 bytes. Later boundaries are unsampled; absence of a later record establishes nothing.

Only pinned reason 1 with halt 4, unchanged head EIP, registers and cache state is classified as pending yield before instructions. Other transitions remain UNKNOWN. A head breakpoint says the current instructions have not yet run at that halt; it does not say no instructions executed earlier in the invocation. Entry counts never establish executed CALLs. Genuine halt/readback checks precede code reads.

Cheap command (under the retained bounded supervisor):

node --max-old-space-size=256 test/test-maelstrom-head-yield-observer.js PINNED_RUN_JS PINNED_EXPORTS_WAT

Controls passed: disabled identity; altered/missing pins; missing/duplicate anchors; early watch conflict with untouched sentinel; all missing exports; wrong halt, EIP, breakpoint and instruction readback; misleading counters and halts; skipped runner boundaries; bounded output; syntax of transformed runner/native fixture; no extra run or observer writes. Existing accepted tools and default/interior assertions are unchanged. Exact-revision native acceptance at 369ba073 is reused only as historical evidence; the old probe was not rerun.

The one native attempt used the standing 1879746-byte module SHA-256 8fac39936b6df2418ad86cab118cef19a65a727f649fbc14c412b37818904686, source b41a7c5f4b752d1f0bdab1141a11d4fed4dc6f9a, ABI 291/layout 9a3bc9149d58209c, fixed shared 512 MiB arena and Node heap 512 MiB. Native admission passed with MemAvailable 2915176448; CPU 90 s/wall 60 s, output 131072, per file 24 MiB, exclusive /tmp/wine-ops-heavy-runtime.lock. It instantiated exactly once and executed only a synthetic CPU microprogram. All native child processes exited naturally and were reaped.

Disjoint off-control 0x7a3c62/66 started with counts [0,0] before any run. Five pending-yield entries alternated halts 5/4/5/4/5, head counts 0/1/1/2/2, unchanged EBP/ESP and zero cache-store growth. Clearing yield consumed the head skip, executed MOV/CALL/synthetic RET/CMP/JMP and halted at the head with EBP=EAX. The final real interior breakpoint reached 0x7a3c66, but interior count was 2, not the fixture's expected 1. Pinned set_bp preserves bp_skip_once: the earlier head halt's skip carries into the first interior arrival; it counts and loops, then the second arrival halts. This was an independent fixture oracle failure. The on lane did not run. It provides no evidence of observer correctness or original-game causality.

The corrected fixture expects [0,0,0,0,0,1,2] interior counts and a cleanup count of 3. Retained off rows match the correction in a static replay; corrected native execution remains untested. A new native attempt requires a coordinator assignment and fresh resource admission, not an unchanged retry in this task.

Evidence is sealed in the adjacent maelstrom-head-yield-observer-20261024/ directory. Full operational evidence and recovered exact blobs remain under /tmp/maelstrom-head-yield-observer-oct24/ops. Recovery uses the immutable manifest /tmp/maelstrom-native-errno-capture-oct24/manifest.json, SHA-256 86111762b21d2c589925d13686bb2285bed23c89cce5243d1c27c407beb244fe, and its runner donor/revision; export source is recovered from that same revision and hash checked. No broad checkout or donor mutation occurred. The initial manifest capture exceeded the requested read bound and was truncated; subsequent inspection selected entries in process. That procedural mistake is retained in admission.json.

Disk receipts count sparse checkout/Git, copies, temp/evidence, full external session and launcher logs, positive SQLite high-water growth, future growth and 8 MiB reserve inside 64 MiB, plus the other worker's reservation and host floor. Standing tools and read-only donor inputs are separately recorded. No main merge.