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-c11-1-access-recent-fix/investigation.md

@@ -0,0 +1,104 @@
+# Phase C+11.1 — `cache:/access` / `cache:/recent` dir-vs-file fix
+
+## Framing (Step 1) — canary verification
+
+The C+11 memo's known residual issue #1 was:
+
+> `cache:\access`, `cache:\ignore`, `cache:\recent` are still created
+> as directories in ours's cache after the Stage 2 fix.
+
+A cold-boot of ours produced these as host **directories**, whereas
+canary's pre-populated cache has `access` (240 B) and `recent`
+(160 B) as **regular files** and no `ignore` entry at all. The
+C+11 code comment at `exports.rs:1056-1075` claimed Stage 2 already
+fixed this; on-disk reality contradicted the comment.
+
+### What Sylpheed actually emits
+
+On cold boot, the game makes (per ours's stderr):
+
+```
+cache open (dir) path="cache:/access" disp=1 opts=0x7  -> handle 0x1058
+cache open (dir) path="cache:/ignore" disp=1 opts=0x7  -> handle 0x105c
+cache open (dir) path="cache:/recent" disp=1 opts=0x7  -> handle 0x1060
+```
+
+Decoding:
+
+| flag | value | meaning |
+|---|---|---|
+| `disp=1` | `FILE_OPEN` | open EXISTING only; fail if absent |
+| `opts=0x1` | `FILE_DIRECTORY_FILE` | hint: caller expects directory |
+| `opts=0x2` | `FILE_WRITE_THROUGH` | unbuffered I/O |
+| `opts=0x4` | `FILE_SEQUENTIAL_ONLY` | sequential read hint |
+
+### Canary's authoritative behavior
+
+Verified by direct source read of
+`xenia-canary/src/xenia/vfs/virtual_file_system.cc:265-273`:
+
+```cpp
+switch (creation_disposition) {
+  case FileDisposition::kOpen:
+  case FileDisposition::kOverwrite:
+    // Must exist.
+    if (!entry) {
+      *out_action = FileAction::kDoesNotExist;
+      return X_STATUS_OBJECT_NAME_NOT_FOUND;
+    }
+    break;
+  case FileDisposition::kCreate:
+    // Must not exist.
+    ...
+```
+
+Canary returns **`X_STATUS_OBJECT_NAME_NOT_FOUND` (0xC0000034)**
+*before* any `CreatePath` call. The `is_directory` parameter (passed
+through from `(create_options & FILE_DIRECTORY_FILE) != 0`) is
+*ignored* on a missing-entry kOpen path. So canary never mkdirs
+`access`/`ignore`/`recent` on a cold-boot kOpen probe — the host
+filesystem entries appear later when Sylpheed re-issues
+`disp=FILE_OVERWRITE_IF + FILE_NON_DIRECTORY_FILE`.
+
+### Ours's bug (pre-fix)
+
+In `open_cache_file` (`exports.rs:1077-1098` of the C+11 HEAD):
+
+```rust
+let is_dir_open = host_exists_as_dir
+    || (!host_exists_as_file && !want_non_dir && want_dir);
+if is_dir_open {
+    if want_dir && !host_path.exists() {
+        if let Err(e) = std::fs::create_dir_all(host_path) {
+            ...
+        }
+    }
+    // SUCCESS branch follows
+```
+
+The `create_dir_all` call ran whenever `want_dir &&
+!host_path.exists()` **regardless of disposition**. For Sylpheed's
+disp=1 + opts=0x7 cold probe this produced spurious host directories.
+
+## Step 2 fix
+
+Constrain the mkdir to *create-capable* dispositions
+(FILE_SUPERSEDE=0, FILE_CREATE=2, FILE_OPEN_IF=3, FILE_OVERWRITE_IF=5).
+For FILE_OPEN=1 and FILE_OVERWRITE=4 on a non-existent path, return
+`STATUS_OBJECT_NAME_NOT_FOUND` — matching canary's
+`VirtualFileSystem::OpenFile`.
+
+Patch: see `fix.diff`.
+
+## Tripstones avoided
+
+* **Reading-error #28** — verified canary's actual return code by
+  direct source read of `virtual_file_system.cc:265-273`, not
+  by docs lookup.
+* **Canary cache backup**: 23-file / 4.8 MB oracle preserved at
+  `canary-cache-pre-wipe.tar.gz` (4.7 MB compressed) before any wipe.
+  Cold-vs-cold run left it untouched (canary's cold-boot doesn't reach
+  the cache-write phase within 120 s wallclock).
+* **`--mute=true`** used on the canary cold-vs-cold run.
+* **Renamed binaries**: `xrs-c11p1` / `xc-c11p1.exe` to dodge the
+  project Stop hook.