Prepare document snapshots before legacy saves

docs/modernization/roadmap.md

@@ -669,7 +669,11 @@ frame durations, captured RGBA8 face payloads, and remaining renderer
 payload-readback counts; the retained `legacy_document_canvas_services` bridge
 now builds the same metadata snapshot from live `Canvas` state and has an
 opt-in dirty-face payload snapshot path backed by retained `Layer::snapshot()`
-readback while live save/export adoption remains under `DEBT-0010`/`DEBT-0036`.
+readback. Live Save, Save As, Save Version, and save-before-workflow paths now
+prepare and log a payload-completeness report from that snapshot before
+delegating to retained `Canvas::project_save`; pure PPI writer replacement,
+export adoption, and renderer-owned readback remain under
+`DEBT-0010`/`DEBT-0013`/`DEBT-0036`.
 `pano_cli plan-image-import` exposes app-core planning for File > Import image
 route decisions, including wide equirectangular images, legacy vertical cube
 strips, regular transform-placement images, and invalid image dimensions; live
@@ -2203,6 +2207,13 @@ Results:
   rejection smoke passed and expose live-canvas-to-`pp_document` projection,
   including captured-versus-pending renderer payload-readback counts, as JSON
   automation.
+- Live Save, Save As, Save Version, and save-before-workflow execution now
+  prepare a payload-bearing canvas document snapshot and save-readiness report
+  through `src/legacy_document_session_services.*` before delegating to the
+  retained `Canvas::project_save` writer, keeping behavior stable while moving
+  the app path onto the document/canvas boundary.
+- `pano_cli plan-canvas-document-snapshot` now emits the same save-readiness
+  report (`payloadComplete` and `canExportPpi`) used by the live save bridge.
 - `pp_app_core_document_import_tests` passed, covering wide equirectangular,
   legacy vertical cube strip, regular transform-placement, and invalid-dimension
   import route decisions, equirectangular service dispatch, transform import
@@ -2469,6 +2480,11 @@ Results:
 - `pano_cli apply-stroke-script` exposes file-driven stroke-script application
   to a pure document face payload and writes a PPI artifact for inspect/load
   round-trip automation.
+- Live document save/session paths consume the payload-bearing canvas snapshot
+  boundary before retained PPI serialization: existing Save, Save As, Save
+  Version, and save-before-workflow now log payload completeness and PPI
+  readiness from `pp_app_core` while legacy `Canvas::project_save` still owns
+  the actual file write, progress/threading behavior, and compatibility quirks.
 - Snapshot creation now rejects invalid embedded RGBA8 face payloads before
   document export or history can persist malformed state.
 - Package-smoke wrappers validate the Windows CMake app executable/runtime