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-w-wedge-reattack/fix.diff

@@ -0,0 +1,30 @@
+--- a/xenia-rs/crates/xenia-kernel/src/exports.rs
++++ b/xenia-rs/crates/xenia-kernel/src/exports.rs
+@@ stub_return_zero …
+ fn stub_return_zero(ctx: &mut PpcContext, _mem: &GuestMemory, _state: &mut KernelState) {
+     ctx.gpr[3] = 0;
+ }
+
++/// Phase W: a literal `return 1`. Matches canary's
++/// `VdInitializeEngines_entry` in `xboxkrnl_video.cc:271-279` which
++/// returns `1` (truthy success token) rather than STATUS_SUCCESS=0.
++/// Sylpheed-side guest code branches on this non-zero, so returning
++/// 0 made the game skip the VdInitializeRingBuffer-and-after init
++/// sequence and never set up the post-init render-target state.
++fn stub_return_one(ctx: &mut PpcContext, _mem: &GuestMemory, _state: &mut KernelState) {
++    ctx.gpr[3] = 1;
++}
++
+@@ exports table …
+-    state.register_export(Xboxkrnl, 0x01C2, "VdInitializeEngines", stub_success);
++    state.register_export(Xboxkrnl, 0x01C2, "VdInitializeEngines", stub_return_one);
+
+@@ tests mod …
++    /// Phase W: ensure `VdInitializeEngines` writes `r3=1` …
++    #[test]
++    fn vd_initialize_engines_returns_one() {
++        let (mut ctx, mem, mut state) = fresh();
++        ctx.gpr[3] = 0xDEAD_BEEF; // sentinel — must be overwritten
++        stub_return_one(&mut ctx, &mem, &mut state);
++        assert_eq!(ctx.gpr[3], 1, "stub_return_one must put 1 in r3");
++    }