intro-video RE: deep demux-core instrumentation + handoff hygiene

Investigation probes for the ADV.wmv intro-video deadlock (feeder's demux
source-read 0x825211a0 returns no-data 0x80500000 where canary returns 0).

- xenia-kernel/state.rs: extend AUDIT-DEREF (fire_audit_pc_probe_if_match) to
  deep-dump the demux-state object (to +0xfc), its buffer descriptor [sub+4],
  the byte-source sub-objects ([sub+0]/[+0x30]/[+0x94] and [src0+0x2c]), and
  to WALK the windowed-buffer cached-block linked list (AUDIT-BLK: per-block
  64-bit start/size/dataptr) exactly as mapper 0x82522118 does. Read-only,
  env-gated (XENIA_AUDIT_DEREF); lockstep digest unaffected.
- xenia-app/main.rs: XENIA_DUMP_SLOTS observe-only scheduler runqueue dump.
- xenia-app/tests/sylpheed_oracles.rs: resolve ISO via SYLPHEED_ISO, then the
  repo-root sylpheed.iso symlink, then default; fix path typo.
- .gitignore: exclude .claude/ (71k files / 66GB agent worktrees) and the
  local investigation artifacts (audit-runs/, exit-thread-state.json, zq_*.py).

Findings (full chain in handoff notes): all ASF header metadata parses
correctly (packet size 16415, count 4728, 2 streams); cursors correct
(cur=5868, limit=77.6M); the windowed buffer works and slides (512B blocks);
no-data originates deep in the byte-read/parse chain, not from an empty buffer.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/xenia-app/src/main.rs

@@ -4276,6 +4276,34 @@ fn dump_thread_diagnostic(
     }
     use xenia_kernel::objects::KernelObject;
 
+    // STEP-10 diagnostic (observe-only, env-gated `XENIA_DUMP_SLOTS=1`).
+    // Prints each scheduler slot's full runqueue with the fields needed to
+    // distinguish "Blocked(Suspended) forever" from "Ready but never picked":
+    // tid, handle, state, suspend_count, idx, and the slot's running_idx.
+    // Read-only — no guest state mutation, no scheduler-behavior change — so
+    // the lockstep digest is unaffected. Not gated on `--quiet` so the
+    // documented headless invocation still emits it.
+    if std::env::var("XENIA_DUMP_SLOTS").as_deref() == Ok("1") {
+        println!("\n=== SLOT DUMP (XENIA_DUMP_SLOTS) ===");
+        for (hw_id, slot) in kernel.scheduler.slots.iter().enumerate() {
+            println!("  hw={} running_idx={:?} depth={}", hw_id, slot.running_idx, slot.runqueue.len());
+            for (idx, t) in slot.runqueue.iter().enumerate() {
+                println!(
+                    "    idx={} tid={} handle={:?} state={:?} suspend_count={} pri={} mask={:#04x} pc={:#010x}",
+                    idx,
+                    t.tid,
+                    t.thread_handle.map(|h| format!("{:#06x}", h)),
+                    t.state,
+                    t.suspend_count,
+                    t.priority,
+                    t.affinity_mask,
+                    t.ctx.pc,
+                );
+            }
+        }
+        println!("=== END SLOT DUMP ===\n");
+    }
+
     // Toolkit-audit fix (2026-06-21): only the ALWAYS-ON thread/waiter table
     // is suppressed by `--quiet`. The explicitly-armed diagnostics below
     // (`--trace-handles`, `--trace-handles-focus`, `--dump-addr`) are