Move project save write planning to app core

docs/modernization/roadmap.md

@@ -709,7 +709,11 @@ save-writer route JSON. `pp_app_core` also owns the retained project-save target
 path planner for target, temporary PPI, and timelapse sidecar paths; live
 `Canvas::project_save_thread` consumes that planner and
 `pano_cli plan-canvas-project-save-target` exposes it for automation. The same
-automation now feeds payload-complete snapshots through the shared
+app-core boundary now also plans the retained save write mode, distinguishing
+direct first saves from existing-target temporary writes that swap into place
+and preserving the legacy direct-write fallback when the temporary file cannot
+be opened. The same automation now feeds payload-complete snapshots through the
+shared
 `pp_paint_renderer::prepare_document_frame_export_readiness` report, which
 records renderer-neutral six-face texture upload commands and encodes the
 active document frame's six composited faces to PNG bytes. This gives CLI
@@ -2313,6 +2317,9 @@ Results:
   temporary `.tmp.ppi` path, and timelapse `.pptl` sidecar. The live
   `Canvas::project_save_thread` consumes the same planner before retained
   serialization, reducing inline path compatibility logic in the legacy writer.
+  It also reports the app-core write-mode plan for direct first saves versus
+  existing-target temporary writes, including the retained fallback to direct
+  target writes when the temporary file cannot be opened.
 - The same payload-complete snapshot automation now uploads the active document
   frame through `pp_paint_renderer::upload_document_frame_faces` and the
   `RecordingRenderDevice`, emitting `rendererUpload` JSON with texture,