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>

audit-runs/phase-host-audio-eager/re-validation.md

@@ -0,0 +1,127 @@
+# Phase Host-Audio-Eager — Re-validation (2026-05-19)
+
+## Progression metric (primary gate)
+
+| metric | pre-fix baseline | post-fix | delta |
+|-------:|:----------------:|:--------:|:-----:|
+| **swaps** | 1 | **1** | **0** |
+| **draws** | 0 | **0** | **0** |
+
+**The progression metric did NOT move.** Despite landing the eager-seed
+implementation cleanly with 3× reproducibility, neither swaps nor draws
+advanced. This matches the prior agent's diagnosis: the audio worker
+ordering issue is real, but the deeper root cause is voice-struct state
+divergence — the audio callback at `0x824D6640` in ours blocks on
+`KeWaitForMultipleObjects([0x82928B04, 0x82928AE0])` immediately
+because the voice struct at `[r31+356]` reads `0x01` (ours) vs `0x00`
+(canary). Pre-seeding 8 fires lets `try_inject_audio_callback` deliver
+the first callback earlier, but the callback still blocks on the same
+guest dispatchers — fires 2-8 sit in the queue because
+`interrupts.is_in_callback()` stays true.
+
+## 3× determinism
+
+```
+73e99d60029128b4d5c3dd98e540457d82a52b8a962e7495132be2be31411aca  /tmp/digest_eager_1.json
+73e99d60029128b4d5c3dd98e540457d82a52b8a962e7495132be2be31411aca  /tmp/digest_eager_2.json
+73e99d60029128b4d5c3dd98e540457d82a52b8a962e7495132be2be31411aca  /tmp/digest_eager_3.json
+```
+
+All three cold runs produce byte-identical digest JSON. The
+seed-at-register implementation is fully deterministic in lockstep
+mode (the ticker accumulator gets pre-populated synchronously inside
+the register handler, no host-thread non-determinism).
+
+## Digest JSON
+
+```json
+{
+  "instructions": 50000007,
+  "imports": 40390,
+  "unimpl": 0,
+  "draws": 0,
+  "swaps": 1,
+  "unique_render_targets": 0,
+  "shader_blobs_live": 0,
+  "texture_cache_entries": 0
+}
+```
+
+`imports`/`unimpl` unchanged from the C+22 baseline (40390/0).
+
+## Phase B invariant
+
+```
+image_loaded_sha256 = ea8d160e9369328a5b922258a92113efb8d7ce3e1a5c12cc521e375985c91c18
+```
+
+UNCHANGED — Phase B is not affected by audio-runtime changes.
+
+## Per-chain matched-prefix
+
+100M-instruction cold trace vs canary baseline
+(`xenia-rs/audit-runs/phase-d-stage1/canary-cvaroff-trunc.jsonl` —
+pre Phase D D-extension absorber, so main reads at the C+18
+102,424 value, NOT the post-D-extension 105,046).
+
+| chain | pre-fix | post-fix | delta | first divergence |
+|------:|--------:|---------:|------:|:-----------------|
+| canary tid=4 → ours tid=11 | 11 | **11** | 0 | (preserved) |
+| canary tid=6 → ours tid=1 | 102,424 | **102,424** | **0** | `NtQueryFullAttributesFile` (C+18-era) |
+| canary tid=7 → ours tid=2 | 32 | **32** | 0 | (preserved) |
+| canary tid=12 → ours tid=7 | 4 | **4** | 0 | C+23 idx=4 |
+| canary tid=14 → ours tid=9 | 41 | **41** | 0 | (no advance — primary target) |
+| canary tid=15 → ours tid=10 | 16 | **16** | 0 | (no advance — primary target) |
+
+The two primary targets (tid=14→9 and tid=15→10) were the audio worker
+guest threads spinning on the uninitialized voice struct. Their
+matched-prefix did NOT advance.
+
+## Kernel tests
+
+- Pre: 217 passed
+- Post: **221 passed** (+4 new `seed_fires_for_*` tests)
+- Failures: 0
+- All existing tests pass
+
+## Build
+
+`cargo build --release` clean. One pre-existing dead-code warning
+unrelated to this fix.
+
+## Total LOC
+
+| file | added | removed |
+|------|------:|--------:|
+| `crates/xenia-kernel/src/xaudio.rs` | 86 | 0 |
+| `crates/xenia-kernel/src/exports.rs` | 18 | 5 |
+| **total** | **104** | **5** |
+
+Net ~100 LOC, of which ~60 LOC are tests + doc comments. Engine logic
+delta is ~25 LOC.
+
+## Conclusion
+
+The implementation lands cleanly:
+- 3× cold-deterministic
+- Phase B unchanged
+- All tests pass
+- Sister chains preserved
+
+But the progression metric (swaps/draws) did NOT move. This is an
+HONEST NEGATIVE RESULT: the eager-seed approach addresses the symptom
+(ticker delays the first callback) but not the root cause (the
+callback at 0x824D6640 still blocks on guest dispatchers that only
+tid=9/10 can signal, and tid=9/10 are stuck on a voice-struct field
+that the callback would need to clear — but doesn't, because canary's
+callback takes a DIFFERENT control-flow path that doesn't reach the
+KeWaitForMultipleObjects in the first place).
+
+The deeper fix requires either:
+- Identifying the guest write that initializes `[r31+356]` to 0 in
+  canary's boot path and ensuring ours produces the same write.
+- A true host-side audio worker thread that can run the callback
+  in a host context (substantial threading-model rework).
+
+Both are out of scope for this session per the brief's "Don't widen
+scope" tripstone.