IOS LLE: optional IPC request/reply metadata trace (StarletOS phase 11 L2)

With DOLPHIN_IPC_TRACE=1 and the original IOS on the emulated Starlet, log
each request Broadway posts (X1: command, descriptor, argument words, an
OPEN's path) and each reply Starlet posts (Y1: original command, result).
Buffer contents are never read; nothing changes without the variable.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

docs/StarletOS_Checkpoint.json

@@ -46,6 +46,11 @@
       "sha256": "7e9bcfff87f526510aad149e781ae57140e32f7b32beafec00271fbcdb152848",
       "bytes": 4526
     },
+    {
+      "path": "Source/Core/Core/HW/WII_IPC.cpp",
+      "sha256": "e216d272f7653b4650481a3335989a86550eee3d90aa7e6c7f06bb1ce87822e1",
+      "bytes": 21443
+    },
     {
       "path": "Source/Core/Core/IOS/Starlet/ARMCore.cpp",
       "sha256": "40d45aed7c5edb4540105dcdee4dd8dcde88c21ba7f3279eff0a9564f2d02a29",
@@ -122,5 +127,14 @@
     "unpublishedHistoricalFileVersionsScanned": 67,
     "privateFindings": 0,
     "newFullBuildOrHardwareTest": "NOT RUN: publication of existing qualified bytes only; see companion phase reports"
-  }
+  },
+  "updates": [
+    {
+      "recordedAt": "2026-10-06",
+      "purpose": "StarletOS Phase 11 proposal L2: IPC request/reply metadata trace while the original IOS runs (DOLPHIN_IPC_TRACE=1); no behavior change otherwise",
+      "files": [
+        "Source/Core/Core/HW/WII_IPC.cpp"
+      ]
+    }
+  ]
 }