Checkpoint 2: integrate native Editor, MCP, gameplay builds and standalone export

docs/IMPLEMENTATION.md

@@ -28,9 +28,60 @@ Observed validation on Linux:
 - MkDocs strict build passed with MkDocs 1.6.1 and Material 9.7.7.
 
 The full editor, user-project build pipeline, MCP integration, standalone exports,
-and Windows acceptance are still being implemented. This checkpoint is not the MVP release.
+and Windows acceptance were still being implemented at that checkpoint. Later progress is recorded below.
 
 Known intermediate constraints include box-only physics colliders, root-level physics
-objects, static glTF triangles/UV0, a conservative serial renderer, and unfinished
-world-preserving authoring reparent operations. These remain implementation work or
+objects, static glTF triangles/UV0, a conservative serial renderer, and then-unfinished
+world-preserving authoring reparent operations (completed in checkpoint 2). These remain implementation work or
 explicit profile limits to review during final acceptance.
+
+## Checkpoint 2 — integrated Editor, gameplay iteration and export
+
+Implemented and integrated:
+
+- Separate Player and SchemaExporter executables; statically linked project gameplay,
+  configurable simulation settings, real contact-based grounded queries, and four
+  compiled scripting tutorials embedded directly into the English MkDocs manual.
+- Shared authoring commands and a real stdio MCP server, optimistic revisions,
+  transactional retries, jobs/cancellation, recovery of unsaved documents, and
+  viewport capture in graphical sessions only.
+- Cancellable native subprocess execution, incremental project builds, schema export,
+  binary scene/resource packaging, distinct Debug development and Release export
+  directories, immutable published generations and retained last-good builds.
+- A native retained UI with pinned FreeType/HarfBuzz and bundled Noto Sans:
+  scene tree, schema Inspector, viewport camera/picking/gizmos, assets, diagnostics,
+  build/play controls, commands, recovery and startup-loaded extension action panels.
+- Exact-build native Editor SDK, dependency validation, owner-bound registrations,
+  example Beacon runtime component/editor command/panel, and unknown-data preservation.
+- Full world-preserving TRS reparent with explicit rejection of unsupported shear.
+- Read-only cooked asset target for Player. Import/build/editor/MCP services remain
+  outside the shipping runtime dependency graph.
+
+Observed validation:
+
+- Integrated Linux Clang 21 build: 19 CTests pass, including GPU rendering, retained
+  widgets, Editor authoring interaction, actual plugin loading, real MCP stdio,
+  process/cook contracts, and all four compiled gameplay tutorials.
+- Real 2D and imported-glTF 3D standalone exports render with zero Vulkan validation
+  errors on NVIDIA RTX 2080 Ti. Changing gameplay rebuilds metadata; failed C++
+  compilation preserves the last successful published build.
+- Runtime/tutorial checks also pass with Clang 18; runtime ASan/UBSan checks pass.
+- Unmodified Blender 4.5.3 exports through the optional add-on. Real Editor imports
+  preserve output IDs after rename/geometry edits, report deleted-output conflicts,
+  retain the last generation on failure, and preserve separate scene placement/color.
+  Reproduce with `tools/verify_blender_roundtrip.py --blender PATH --editor PATH`.
+- Strict MkDocs build passes. Tutorial source snippets are compiled by CTest.
+- Previous checkpoint headless Linux and Windows GitHub CI passed after portability
+  fixes. New checkpoint and full Windows graphical/export checks are separate work;
+  Linux validation does not imply Windows validation.
+
+This is an implementation checkpoint, not an MVP release. Finished playable sample
+projects, complete Windows graphical/export acceptance, fresh-install checks,
+performance measurements, and final UX review remain. Standalone image import is
+integrated but its dedicated PNG/JPEG edge-case checks are the next asset task.
+
+The baseline profile currently uses box colliders, root-level rigid bodies, static
+triangle glTF meshes/UV0, basic PBR/directional shadows and a conservative serial
+Vulkan renderer. Advanced rendering and broader content profiles remain later work.
+The generated UI reference determines visual direction only; architecture, behavior
+and acceptance criteria remain authoritative.