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/fix.diff

@@ -0,0 +1,105 @@
+Phase C+11.1 — `cache:/access` / `cache:/recent` dir-vs-file fix
+================================================================
+
+File: crates/xenia-kernel/src/exports.rs
+Function: open_cache_file
+
+Hunk 1: replace the post-existing-file-wins block with a
+disposition-gated mkdir + STATUS_OBJECT_NAME_NOT_FOUND on miss.
+
+Pre-fix (Phase C+11 HEAD):
+
+    let host_exists_as_dir = host_path.is_dir();
+    let host_exists_as_file = host_path.is_file();
+    let is_dir_open = host_exists_as_dir
+        || (!host_exists_as_file && !want_non_dir && want_dir);
+    if is_dir_open {
+        // For non-existent paths the guest wants us to create as a
+        // directory, mkdir-p; canary's HostPathDevice does the same
+        // when FILE_DIRECTORY_FILE is set on a kCreate disposition.
+        if want_dir && !host_path.exists() {
+            if let Err(e) = std::fs::create_dir_all(host_path) {
+                ...STATUS_UNSUCCESSFUL...
+            }
+        }
+        // ... falls through to SUCCESS / handle alloc
+
+Post-fix (Phase C+11.1):
+
+    let host_exists_as_dir = host_path.is_dir();
+    let host_exists_as_file = host_path.is_file();
+    let is_dir_open = host_exists_as_dir
+        || (!host_exists_as_file && !want_non_dir && want_dir);
+    if is_dir_open {
+        // Phase C+11.1 — only create the host directory when the
+        // disposition is *create-capable*. Mirrors canary's
+        // `VirtualFileSystem::OpenFile` (virtual_file_system.cc:265-273):
+        // for `FileDisposition::kOpen`/`kOverwrite` on a non-existent
+        // path the function returns `X_STATUS_OBJECT_NAME_NOT_FOUND`
+        // *before* any `CreatePath` call — i.e. mkdir is never invoked
+        // on these dispositions. The pre-fix code (Phase C+11) called
+        // `create_dir_all` whenever `want_dir && !host_path.exists()`,
+        // so Sylpheed's cold-boot probes for `cache:/access`,
+        // `cache:/ignore`, `cache:/recent` (disp=1, opts=0x7) succeeded
+        // and produced spurious host directories. Canary instead
+        // returns NOT_FOUND, after which Sylpheed re-creates these as
+        // FILES via `disp=5` + `FILE_NON_DIRECTORY_FILE`.
+        //
+        // Create-capable dispositions (mkdir OK):
+        //   0 FILE_SUPERSEDE
+        //   2 FILE_CREATE
+        //   3 FILE_OPEN_IF
+        //   5 FILE_OVERWRITE_IF
+        // Non-create dispositions (must miss when path is absent):
+        //   1 FILE_OPEN
+        //   4 FILE_OVERWRITE
+        let disp_is_create_capable = matches!(
+            create_disposition,
+            FILE_SUPERSEDE | FILE_CREATE | FILE_OPEN_IF | FILE_OVERWRITE_IF
+        );
+        if !host_path.exists() {
+            if !disp_is_create_capable {
+                if handle_out != 0 {
+                    mem.write_u32(handle_out, 0);
+                }
+                write_io_status_block(
+                    mem,
+                    io_status_block,
+                    STATUS_OBJECT_NAME_NOT_FOUND as u32,
+                    0,
+                );
+                tracing::info!(
+                    "cache open (dir) MISS path={:?} disp={} opts={:#x} -> NOT_FOUND",
+                    guest_path,
+                    create_disposition,
+                    create_options
+                );
+                return STATUS_OBJECT_NAME_NOT_FOUND;
+            }
+            // create-capable + want_dir → mkdir-p the directory.
+            if want_dir {
+                if let Err(e) = std::fs::create_dir_all(host_path) {
+                    ...STATUS_UNSUCCESSFUL...
+                }
+            }
+        }
+        // ... falls through to SUCCESS / handle alloc as before
+
+Hunk 2 (tests): two new unit tests added in
+crates/xenia-kernel/src/exports.rs after
+`cache_top_level_manifests_create_as_files`:
+
+  - cache_open_directory_on_missing_path_returns_not_found
+    Loops over the three cold-probe paths Sylpheed actually emits
+    (cache:\\access, cache:\\ignore, cache:\\recent) and asserts
+    NtCreateFile + disp=1 + opts=0x7 returns NOT_FOUND, writes
+    handle=0, and leaves no host entry on disk.
+
+  - cache_disp5_after_disp1_miss_creates_file
+    Pins the canary two-call sequence: cold disp=1 returns NOT_FOUND;
+    immediately following disp=5 + opts=0x60 (FILE_NON_DIRECTORY_FILE)
+    succeeds and produces a host FILE.
+
+LOC summary: ~30 added in open_cache_file (mkdir gate + NOT_FOUND
+return branch + comments), ~6 removed (the unconditional mkdir
+flow); ~88 lines of test code for the two new tests.