Move project save write planning to app core

docs/modernization/build-inventory.md

@@ -301,8 +301,11 @@ powershell -ExecutionPolicy Bypass -File scripts\automation\apple-remote-build.p
   retained project-save target paths, including the requested PPI path,
   temporary `.tmp.ppi` path, and timelapse `.pptl` sidecar path. The live
   `Canvas::project_save_thread` consumes the same planner before retained
-  serialization, and the command is covered by forward-slash, Windows
-  backslash, and invalid-path smokes.
+  serialization. The command also reports the app-core write-mode plan for
+  direct first saves versus existing-target temporary writes, including the
+  retained direct-write fallback when the temporary file cannot be opened, and
+  it is covered by forward-slash, Windows backslash, existing-target, and
+  invalid-path smokes.
 - Live equirectangular, layer, animation-frame, and cube-face export adapters
   now prepare and log the same payload-bearing canvas document snapshot plus
   shared paint-renderer export-readiness report.
@@ -1182,7 +1185,8 @@ powershell -ExecutionPolicy Bypass -File scripts\automation\apple-remote-build.p
   prepare and log a payload-bearing canvas document snapshot report, run the
   app-core pure PPI save-writer route for payload-complete snapshots, log
   generated byte counts, and derive project-save target/tmp/timelapse paths
-  through `pp_app_core` before delegating to retained `Canvas::project_save`.
+  plus direct-vs-temporary write-mode decisions through `pp_app_core` before
+  delegating to retained `Canvas::project_save`.
   Retained legacy UI/canvas
   execution and actual live save serialization remain tracked by `DEBT-0040`,
   `DEBT-0041`, and `DEBT-0042`; the pure snapshot-to-PPI export handoff is