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/tests/sylpheed_oracles.rs

@@ -24,10 +24,25 @@
 
 use std::process::Command;
 
-const ISO_DEFAULT: &str = "/home/fabi/RE Project Sylpheed/Project Sylpheed - Arc of Deception (USA, Europe) (En,Ja).iso";
+const ISO_DEFAULT: &str = "/home/fabi/RE - Project Sylpheed/Project Sylpheed - Arc of Deception (USA, Europe) (En,Ja).iso";
 
+/// Resolve the Sylpheed ISO, in priority order:
+///   1. `SYLPHEED_ISO` env var (explicit override),
+///   2. the repo-root `sylpheed.iso` symlink (the documented per-machine
+///      setup — see HANDOFF §0b), so a standard checkout runs without env vars,
+///   3. a last-resort absolute default.
+/// Returns the first existing path, else the default string so the caller's
+/// existence check still produces the "SKIPPING" message.
 fn iso_path() -> String {
-    std::env::var("SYLPHEED_ISO").unwrap_or_else(|_| ISO_DEFAULT.to_string())
+    if let Ok(p) = std::env::var("SYLPHEED_ISO") {
+        return p;
+    }
+    // Repo root is two levels up from this crate's manifest dir.
+    let symlink = std::path::Path::new(env!("CARGO_MANIFEST_DIR")).join("../../sylpheed.iso");
+    if symlink.exists() {
+        return symlink.to_string_lossy().into_owned();
+    }
+    ISO_DEFAULT.to_string()
 }
 
 fn run_oracle(label: &str, max_instr: u64, golden_rel: &str) {