Expose asset timestamp probe boundary

docs/modernization/debt.md

@@ -242,6 +242,11 @@ agent or engineer to remove them without reconstructing context from chat.
   `plan_asset_file_load` wrapper still performs the retained `stat` probe for
   mtime platforms until asset/file watching is owned by injected storage
   services.
+- 2026-06-12: DEBT-0054 was narrowed again. The retained mtime probe is now an
+  explicit `pp_platform_api::probe_asset_file_timestamp` boundary with missing
+  and existing file coverage, and `plan_asset_file_load_for_platform` consumes
+  that probe instead of owning the `stat` call inline. Injected file-watch or
+  storage services still need to own the live probe before the debt closes.
 - 2026-06-05: DEBT-0056 was narrowed. `src/asset.h` no longer exposes Android
   SDK types or forward declarations; retained Android asset-manager and asset
   handles are stored as opaque pointers and cast only inside `src/asset.cpp`,

docs/modernization/roadmap.md

@@ -644,6 +644,8 @@ mobile platform keyboard bridges continue.
 `pano_cli plan-cursor-visibility` exposes the app-core cursor visibility
 decision used by live canvas cursor requests before retained desktop platform
 cursor bridges continue.
+`pp_platform_api::probe_asset_file_timestamp` now owns the retained asset mtime
+probe used by layout reload planning, with missing/existing file coverage.
 `pano_cli plan-clipboard-read` and `pano_cli plan-clipboard-write` expose the
 app-core clipboard text decisions used by live clipboard get/set requests
 before retained platform clipboard bridges continue.