Add document export CLI automation

docs/modernization/roadmap.md

@@ -352,6 +352,9 @@ exposes the generated writer for metadata-only and test dirty-face-payload
 round-trips through `load-project`.
 `pp_document::export_ppi_project_document` converts pure documents into PPI
 bytes using that writer, including PNG-encoded layer/frame face payloads.
+`pano_cli simulate-document-export` exercises that pure document export path,
+decodes the generated PPI bytes, reimports them, and emits JSON round-trip
+metadata.
 `pano_cli create-document` can create simple animation documents with explicit
 frame count/duration. `pano_cli simulate-document-edits` exercises pure
 layer metadata, frame reordering, active-index preservation, tiny face-payload
@@ -359,6 +362,8 @@ attachment, and selection-mask attachment. `pano_cli simulate-document-history`
 pure `pp_document::DocumentHistory` apply/undo/redo path and emits JSON state
 summaries. `pano_cli simulate-image-import` decodes an embedded tiny PNG
 through `pp_assets` and attaches the resulting RGBA8 payload to `pp_document`.
+`pano_cli simulate-document-export` exercises pure document-to-PPI export,
+asset-level PPI image decode, and document reimport in one automation command.
 `pano_cli simulate-stroke` exercises the pure stroke sampler for
 scripted-stroke automation. `pano_cli simulate-stroke-script`
 loads stroke script fixtures, parses them through `pp_paint`, and samples every
@@ -716,6 +721,9 @@ Results:
   state as JSON.
 - `pano_cli_simulate_document_history_smoke` passed and reports real
   `pp_document::DocumentHistory` apply/undo/redo state as JSON.
+- `pano_cli_simulate_document_export_smoke` passed and reports pure
+  `pp_document` export to PPI bytes, asset-level decode, and document reimport
+  round-trip state as JSON.
 - `pano_cli_simulate_image_import_smoke` passed and reports embedded PNG decode
   plus `pp_document` face-payload attachment state as JSON.
 - `pano_cli_inspect_image_rejects_unsupported` passed as an expected failure
@@ -814,6 +822,8 @@ Results:
 - `pp_document::export_ppi_project_document` exposes pure document-to-PPI byte
   export through CTest coverage; legacy Canvas save integration remains tracked
   by DEBT-0010/DEBT-0013.
+- `pano_cli simulate-document-export` exposes the same export path through JSON
+  automation for agents.
 - Snapshot creation now rejects invalid embedded RGBA8 face payloads before
   document export or history can persist malformed state.
 - PowerShell package-smoke wrapper validates the Windows CMake app executable