[iterate-2M] PCR+0x10C (PRCB.current_cpu): init per-HW-thread to unwedge spin-barrier

Ours never initialized the PRCB `current_cpu` byte at PCR+0x10C
(prcb_data@0x100 + current_cpu@0xC). Canary sets it from
`GetFakeCpuNumber(affinity)` (xthread.cc:847 `pcr->prcb_data.current_cpu =
cpu_index`), which equals the HW thread id ours already writes at PCR+0x2C.
Left unwritten it read 0 for every thread.

Guest spin-barrier `sub_824D1328` (used by the audio/update pump threads at
entries 0x824D2878 / 0x824D2940, ours tid 9 / tid 10) indexes a per-HW-thread
occupancy byte array via `lbz r11, 268(r13)` then `stbx ..., [array+index]`.
With index 0 for all threads, every thread marked slot 0; the multi-byte
rendezvous signature it then spins on (`ld [obj+0x164]` compared against the
packed per-slot expectation) could never assemble. Both pump threads busied at
pc 0x824d140c/0x824d1410 forever (Ready, 5M+ barrier iterations) and never ran
their `KeSetEvent` loops — so the events they signal (the 21k-per-thread
heartbeat in canary) never fired, starving the downstream worker handshake.

Fix: write `hw_id` to PCR+0x10C alongside PCR+0x2C in both the static thread
image init (thread.rs) and the dynamic PcrWriter (state.rs, used by scheduler
spawn + affinity migration) so the two stay in sync.

Runtime-verified BOTH engines. Post-fix the pump threads escape the barrier
(barrier iterations 5M+ -> 3) and advance into their loop bodies, now correctly
Blocked(WaitAny) at pc 0x824d28d0 / 0x824d29c0 (was spinning at 0x824d140c).
imports at n50M 339,766 -> 451,508; deterministic (two cold runs byte-identical).
draws still 0 (a later, separate render gate). golden re-baselined.
cargo test --workspace: 672 passed, 0 failed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/xenia-app/tests/golden/sylpheed_n50m.json

@@ -1,6 +1,6 @@
 {
-  "instructions": 50000000,
-  "imports": 339766,
+  "instructions": 50000003,
+  "imports": 451508,
   "unimpl": 0,
   "draws": 0,
   "swaps": 2,

crates/xenia-kernel/src/state.rs

@@ -17,6 +17,16 @@ impl PcrWriter for GuestMemoryPcr<'_> {
         // `GuestMemory::write_u32` takes `&self` post-M2 trait flip; the
         // wrapping `&'a GuestMemory` is sufficient.
         self.0.write_u32(pcr_base + 0x2C, hw_id as u32);
+        // PRCB.current_cpu byte at PCR+0x10C (prcb_data@0x100 + current_cpu@0xC).
+        // Canary writes `GetFakeCpuNumber(affinity)` here (xthread.cc:847
+        // `pcr->prcb_data.current_cpu = cpu_index`), which equals the HW thread
+        // id we already compute. Guest spin-barriers (e.g. sub_824D1328, used by
+        // the audio/update pump threads at entries 0x824D2878/0x824D2940) index a
+        // per-HW-thread occupancy array by `lbz r11, 268(r13)` = this byte. Left
+        // unwritten it stayed 0 for every thread, so all threads collided on
+        // slot 0 and the multi-thread rendezvous signature never assembled —
+        // the pump threads spun forever and never fired their KeSetEvent loops.
+        self.0.write_u8(pcr_base + 0x10C, hw_id);
     }
 }
 

crates/xenia-kernel/src/thread.rs

@@ -57,6 +57,11 @@ pub fn allocate_thread_image(
     mem.write_u32(pcr_base, tls_base);
     mem.write_u32(pcr_base + 0x2C, hw_thread_id as u32);
     mem.write_u32(pcr_base + 0x100, 0x1000);
+    // +0x10C  prcb_data.current_cpu — canary `pcr->prcb_data.current_cpu`
+    //         (PRCB@0x100 + current_cpu@0xC). Guest spin-barriers index a
+    //         per-HW-thread slot array by `lbz r11, 268(r13)` = this byte; it
+    //         must equal the HW thread id (== PCR+0x2C). See state.rs PcrWriter.
+    mem.write_u8(pcr_base + 0x10C, hw_thread_id);
     mem.write_u32(pcr_base + 0x150, 0);
 
     Some(ThreadImage {