handoff: VSync/event-wedge fixes + iterate 2.A–2.BC research notes
Source changes (dormant parity infra, retained from iterate 2.AI/2.AO): - xenia-kernel/exports.rs: nt_create_event manual_reset polarity + related event wiring - xenia-gpu/mmio_region.rs: D1MODE_VBLANK_VLINE_STATUS hardcode parity Also lands the audit-runs/ analysis notes (.md/.txt/.json digests) for the iterate 2.x VSync/0x10e8/0x1004 wedge investigation. Raw trace dumps (.jsonl/.gz/.csv/.stdout) and agent worktrees (.claude/) are gitignored as regenerable local artifacts — see memory + HANDOFF for the running findings. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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MechaCat02
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audit-runs/audit-069-wait-signal-producer/writer-report-v2.md
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# AUDIT-069 Session 2 — writer report v2
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Date: 2026-05-20
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xenia-rs HEAD: `e6d43a23ac393004d2e5adf2f0395fd0b5e6448b` (UNCHANGED from S1)
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`git diff HEAD | sha256sum`: `ed30fd526643918f67311caff0a10d1346d73fd0c0323e02477883cf5ff20357` (UNCHANGED from S1 end)
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No canary instrumentation added this session.
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## Headline
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**S1's framing is FALSIFIED.** ours does NOT lack a "canary-tid=10
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equivalent" thread. The spawn chain executes identically:
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main (ours tid=1) → sub_8244FEA8 → sub_8244FF50
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→ ExCreateThread(entry=0x82450A28, ctx=0x828F3B68)
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→ ours tid=5 starts
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→ sub_82450A28 (1×) → sub_82450A68 (1×)
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→ γ-signaler family (sub_8245D9D8 6×, sub_8245DA78 1×, sub_8245DB40 75×)
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This is bit-equivalent to canary's chain, modulo the tid label
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(canary calls it tid=10, ours calls it tid=5 — same entry, same ctx,
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same dispatch loop, same γ-signaler family fires from inside it).
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The signaler spawn-chain is NOT the bug. S1's "the bug is at the
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thread-spawn layer" hypothesis is wrong.
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## Spawn chain (DB-derived, READ-ONLY DuckDB)
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| Fn | callers in DB | role |
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|---|---|---|
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| 0x82450A28 | 1 ref-edge from 0x8244FFF8 (sub_8244FF50+0xA8) | thread entry (data ptr only) |
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| 0x8244FF50 | 1 call-edge from 0x8244FEE8 (sub_8244FEA8+0x40) | ExCreateThread caller |
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| 0x8244FEA8 | 11 call-edges (8 unique callers across sub_821A5150, sub_821CB968, sub_821CC2E8, sub_821D2850, sub_82237EC8, sub_8225EE20, sub_822E0350, sub_824528A8, sub_82452DC0 (2×), sub_8245E528) | spawn helper |
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## Per-PC fire counts (ours-cold, 1.5B instr, fresh today)
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| PC | symbol | fires | tid |
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|---|---|---|---|
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| 0x8244FEA8 | sub_8244FEA8 (spawn helper) | 7 | 1 |
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| 0x8244FF50 | sub_8244FF50 (ExCreateThread caller) | 1 | 1 |
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| 0x82450A28 | sub_82450A28 (thread entry) | 1 | 5 |
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| 0x82450A68 | sub_82450A68 (worker dispatch loop) | 1 | 5 |
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| 0x8245D9D8 | γ-signaler D | 6 | 5 |
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| 0x8245DA78 | γ-signaler D-B | 1 | 5 |
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| 0x8245DB40 | γ-signaler D-NEW | 75 | 5 |
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Spawn event log confirms `ExCreateThread: tid=5 handle=0x1050 entry=0x82450a28 start_ctx=0x828f3b68`.
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Total `kernel.calls{name=ExCreateThread} = 10`.
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## Comparison with canary (S1 data — fresh today, not stale)
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| metric | canary | ours |
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|---|---|---|
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| thread with entry=0x82450A28 | tid=10 | tid=5 |
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| start_ctx | 0x828F3B68 | 0x828F3B68 |
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| γ-D family signaler firings | all on tid=10 | all on tid=5 |
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| NtSetEvent fires from γ-D (via wrapper 0x824AA2F0) | confirmed | confirmed |
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The spawn chain and γ-signaler invocation match. The only divergence at the
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signaler call site is **which handle gets signaled**, not whether the
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signaler runs.
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## Divergence point (parent fires, child also fires)
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NONE — every node in the spawn chain fires in ours. The S1-prescribed
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"first ancestor that fires while child does not" never materialises because
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the entire chain is reached identically.
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The actual divergence is downstream of the spawn-chain — at the
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**handle-selection** step inside the γ-signaler family, per AUDIT-062's
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prior finding ("ours's γ-signalers signal WRONG handles — neighbors of the
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wedge handle, not the wedge itself").
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## Gate condition
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There is no gate that ours fails. The control flow reaches the γ-signaler
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and invokes the NtSetEvent wrapper (`sub_824AA2F0`) with bit-identical
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control flow. The argument to NtSetEvent (the handle) is the
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divergent term.
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In the AUDIT-062 archive ours-ntset.jsonl, the γ-D signaler on ours tid=5
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calls NtSetEvent on handles `0x103C`, `0x1068`, `0x106C`, `0x1094`, ...
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These are guest-side handle slots that the *waiter* is NOT waiting on.
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Per S1, canary's wedge waiter (tid=17, tid=26) waits on `F80000A4` and
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`F8000110`. Note that canary's handles are *pseudo-handles* (high-bit
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encoded), while ours's slot allocator hands out normal `0x10xx` IDs —
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a known cross-engine handle convention mismatch already documented
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in AUDIT-019/043/062.
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The semantic question is therefore: **what does the producer compute as
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the "next handle to signal", and is the computation reading
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a different value of the bookkeeping struct in ours vs canary?**
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This is the question AUDIT-062 hit and parked; it must be re-opened
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now that S1 has clarified the producer thread is reached identically.
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## ours-side analog status
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The relevant kernel handlers are:
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- `NtSetEvent` — ours `xenia-kernel/src/exports.rs` is per-AUDIT-062 archive
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bit-equivalent to canary in semantics (signals the event, schedules wakeup).
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Returns SUCCESS in both.
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- `ExCreateThread` — ours bit-equivalent (S2 spawn matches canary trajectory
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ctx + entry + suspended flag).
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- `xeKeWaitForSingleObject` (wedge wait at 0x821CB1DC) — ours behaviour
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matches per AUDIT-049/065 prior work; the WAIT itself is fine, what
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remains broken is the signaler picking the right handle on tid=5.
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Net: NO kernel handler bug. The divergence is **guest-state computed
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inside the γ-signaler family at sub_8245D9D8 / sub_8245DA78 /
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sub_8245DB40** — i.e. data that lives in the queue/list dispatched
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by sub_82450A68.
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## Reading-error #28 reclassification
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S1 inadvertently committed the same class of error documented as #28 in
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prior audit memory: "treating per-engine tid label numerically across
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engines without a tid-mapping translation." S1 used canary's "tid=10"
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verbatim and AUDIT-062's "tid=10: 0 fires" verbatim, concluding "ours's
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thread set lacks the canary-tid=10 equivalent." In reality the same
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guest thread exists on both, with renumbered host-side tid labels.
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The correct cross-engine identity is `(entry_pc, start_ctx)`, not the
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tid integer. S2 re-validates by `entry=0x82450a28 ∧ ctx=0x828f3b68`,
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which uniquely identifies the spawn on both engines.
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Do NOT register a new reading-error #; this is the existing #28 surface.
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## Session 3 recommendation (refined)
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Drop the spawn-chain investigation entirely. The producer thread runs.
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**Path A (RECOMMENDED, ~80 LOC ours-only)**: build a probe of the
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**handle-passed-to-NtSetEvent** on tid=5 (ours) inside the γ-signaler
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PCs, paired with the symmetric `audit_69_event_signal_watch` capture
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from S1 in canary. Compare the *sequence of handle IDs* per signaler
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invocation. The first mismatch identifies the guest-state divergence
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that drives wrong-handle selection.
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Plumbing path: extend `--lr-trace` in ours (`crates/xenia-app/src/main.rs:233-243`)
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to also capture `r3` snapshot at multiple PCs, matching canary's
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audit_69 wrapper-entry capture. Already exists (M12 lr_trace lists
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pc/tid/hw/cycle/r3/r4/r5/r6/lr). Probe ours `0x824AA2F0` and `0x824AAF50`
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entry PCs.
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**Path B (~50 LOC diff-tool)**: extend the diff-events JSONL absorber to
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treat the canary→ours handle-ID mapping as a runtime-discovered alias
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when the underlying dispatcher pointer matches. Doesn't fix the bug,
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absorbs the symptom.
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**Path C (root-cause, larger)**: walk sub_82450A68 dispatch loop body
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disassembly + AUDIT-062 archive to identify which guest-memory struct
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holds the queue of "handles to signal." The wrong handles on ours mean
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this struct gets populated wrong somewhere upstream of tid=5's dispatch
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loop — likely from sub_8244FEA8's 7 fires (which call sites enqueue
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work, and what data is enqueued).
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LOC budget for S3: Path A ~80, Path B ~50, Path C unknown (~200+).
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## Cascade A/B/C/D
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- **A** (DB-derived spawn chain): PASS (11 callers, 1 unique call edge to FF50).
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- **B** (per-fn fire counts ours+canary): PASS (ours fresh, canary from S1 fresh).
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- **C** (divergence-point identification): N/A — no divergence in spawn chain;
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S1 framing falsified. Re-direction recommended.
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- **D** (kernel-handler bit-equivalence check): PASS (NtSetEvent / ExCreateThread
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per AUDIT-062 archive; no new kernel bug detected).
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Net: 3/4 PASS, 1/4 N/A (because the postulated divergence wasn't there).
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## Discipline
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- xenia-rs HEAD UNCHANGED (sha256 of `git diff HEAD` matches S1 end).
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- No canary instrumentation added this session — S1's data is fresh.
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- ours-rs ran with `--ctor-probe` (read-only, lockstep-digest-unaffected
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flag already in main.rs:194).
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- No source modifications to ours.
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- ours-rs cache (none on this host); no canary run, no canary cache to wipe.
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## Artifacts
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```
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audit-runs/audit-069-wait-signal-producer/
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session-2-spawn-walk.log (combined probe + DB queries + fires table)
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writer-report-v2.md (this file)
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s2/ours-probe.stdout (780 lines, 91 CTOR-PROBE records)
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s2/ours-probe.stderr (241 lines, all spawn events + summary)
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```
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No `fix-canary-v2.diff` (no canary instrumentation added).
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