Move project save target planning to app core

docs/modernization/roadmap.md

@@ -705,7 +705,11 @@ save-writer route/byte count before retained save continues. The app-core
 snapshot boundary also has a tested pure PPI export helper, and
 `pano_cli plan-canvas-document-snapshot` runs that helper for payload-complete
 snapshots and reports generated byte/dirty-face summaries plus the same
-save-writer route JSON. The same automation now feeds payload-complete snapshots through the shared
+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
 `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
@@ -2304,6 +2308,11 @@ Results:
   the same save-writer route, and payload-complete snapshots now run the pure
   `pp_document` PPI exporter and decoded-project summary before emitting
   `ppiExport` JSON.
+- `pano_cli plan-canvas-project-save-target` now exposes the app-core planner
+  for retained project-save target paths, including the target PPI path,
+  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.
 - 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,