Load PPI metadata into documents

docs/modernization/roadmap.md

@@ -249,10 +249,10 @@ Goal: make each component reachable by automated tools and future agents.
 Status: in progress. `tests/` exists, `desktop-fast` runs headlessly, and
 PowerShell/bash wrappers exist for
 configure/build/test/analyze/platform-build/package-smoke. `pano_cli` exists
-with JSON automation commands for creating a `pp_document` model and
-inspecting image signatures, PPI headers, and layout XML; full document/app
-integration is debt-tracked as DEBT-0010 and full PPI body parsing is
-debt-tracked as DEBT-0013.
+with JSON automation commands for creating a `pp_document` model, metadata-only
+PPI project loading, and inspecting image signatures, PPI headers, and layout
+XML; full document/app integration is debt-tracked as DEBT-0010 and full PPI
+body parsing is debt-tracked as DEBT-0013.
 
 Implementation tasks:
 
@@ -320,8 +320,9 @@ corrupt/truncated/unsupported, extreme-dimension, and key/value limit tests.
 CPU reference math for the five current shader blend modes, and deterministic
 stroke spacing/interpolation plus a pure text stroke-script parser.
 `pp_document` has
-started with a pure canvas/layer/frame model, layer metadata operations, frame
-move/duration queries, and layer/frame/undo-redo history invariant tests.
+started with a pure canvas/layer/frame model, alpha-lock metadata, snapshot
+construction, layer metadata operations, frame move/duration queries, and
+layer/frame/undo-redo history invariant tests.
 `pp_renderer_api` has started with renderer-neutral
 texture/readback descriptors and validation tests. `pp_paint_renderer` has
 started with deterministic CPU layer compositing over renderer extents using
@@ -331,6 +332,8 @@ input tests.
 `pano_cli inspect-image` exposes PNG IHDR metadata as JSON,
 `pano_cli inspect-project` reports validated PPI thumbnail/body byte layout,
 body summary, layer/frame descriptors, and dirty-face PNG payload metadata, and
+`pano_cli load-project` creates a metadata-only `pp_document` projection for
+representable PPI timelines.
 `pano_cli create-document` can create simple animation documents with explicit
 frame count/duration, and `pano_cli simulate-stroke` exercises the pure stroke
 sampler for scripted-stroke automation. `pano_cli simulate-stroke-script`
@@ -577,8 +580,8 @@ Results:
 - `pp_paint_blend_tests` passed.
 - `pp_paint_stroke_tests` passed.
 - `pp_paint_stroke_script_tests` passed.
-- `pp_document_tests` passed, including frame move, duration, and history
-  invariants.
+- `pp_document_tests` passed, including snapshot construction, alpha-lock
+  metadata, frame move, duration, and history invariants.
 - `pp_renderer_api_tests` passed, including shader descriptor validation.
 - `pp_paint_renderer_compositor_tests` passed.
 - `pp_ui_core_color_tests` passed.
@@ -594,6 +597,8 @@ Results:
 - `pano_cli_inspect_project_layout_smoke` passed and reports PPI
   thumbnail/body byte layout, body summary, layer/frame descriptors, and
   dirty-face PNG payload metadata JSON.
+- `pano_cli_load_project_metadata_smoke` passed and reports a metadata-only
+  `pp_document` projection for the minimal PPI fixture.
 - `pano_cli_parse_layout_smoke` passed.
 - `pano_cli_simulate_stroke_smoke` passed and reports deterministic stroke
   sample counts/distances.