Add frontend production project

docs/PROJECT-STRUCTURE.md

@@ -106,7 +106,7 @@ S:\Game Hacking\Eushully\Himegari\           ← workspace root (three siblings)
     │   ├── opcodes.json                        GENERATED from opcodes.toml (machine view for the C# VM)
     │   └── manifest.json, opcode-coverage.md   (opcode-coverage.md GENERATED from opcodes.toml)
     │
-    ├── engine/                              DELIVERABLE — the .NET VM core (AgeEngine.sln: Age.Engine / Age.Cli / tests)
+    ├── engine/                              DELIVERABLE — the .NET VM/runtime projects and tests (AgeEngine.sln)
     │   ├── Age.Engine/Model/                retained graphics state plus separately navigable public
     │                                       render, transition, diagnostic, and persistence contracts
     │   ├── Age.Engine/Sys4/                 runtime game-root selection, catalog parser, loose-first bounded
@@ -118,6 +118,9 @@ S:\Game Hacking\Eushully\Himegari\           ← workspace root (three siblings)
     │   ├── Age.Engine/Persistence/          native S3SD/S4SD + S3RT codecs, shared payload/ReadTextDB,
     │                                       layout-3 numbered state/history/gfx, DAT/STH pair + BMP codec,
     │                                       and profile-owned state
+    │   ├── Age.Engine.Frontend/             platform-neutral frontend diagnostics/options project: page
+    │                                       locator, timeline/trace/step-limit diagnostics, VM/window launch
+    │                                       options, and performance-frame logging
     │   └── Age.Engine.Text.Windows/         optional exact Windows GDI gray-4 reference backend; kept
     │                                       outside the platform-neutral VM/runtime core
     ├── native/                              authored native runtime boundaries
@@ -147,6 +150,13 @@ surface-transition drawing, raster helpers, and compositor decision logging. `go
 Godot input routing, locator/debug hotkeys, debug-scene dispatch, cursor control, native alerts, and
 full-width text entry.
 
+`engine/Age.Engine.Frontend/` is the production owner of frontend helpers that do not depend on Godot types.
+Both `engine/AgeEngine.sln` and `godot/Himegari.sln` include the project; Godot and `Age.Engine.Tests` consume it
+through project references rather than compiling duplicate linked sources. The first owned cluster contains
+`PageLocatorState`, `GodotTimelineLog`, `GodotTraceSink`, `StepLimitDiagnosticFormatter`, `GodotVmOptions`,
+`PerformanceFrameLog`, and `WindowLaunchOptions`. Movie runtime/decoder helpers remain under `godot/` until their
+separate ownership slices.
+
 `godot/GodotAdvHost.cs` retains cross-domain host coordination. Its partial-class companion
 `godot/GodotAdvHost.AdvText.cs` owns live/retained ADV text, surface glyph rasterization and caching,
 history presentation, message-window alpha, and retained wait-indicator configuration/publication.

docs/remake-architecture-and-roadmap.md

@@ -827,6 +827,13 @@ do not mix mechanical moves with semantic changes.
    code into a small production project referenced by Godot, tests, and the corpus gate. Retain both existing
    solution files because Godot export requires the frontend-local solution.
 
+   **Progress (2026-08-03):** the first bounded build-graph slice introduced the platform-neutral
+   `Age.Engine.Frontend` production project and added it to both existing solutions. Page locator, timeline/trace
+   and step-limit diagnostics, VM/window launch options, and performance-frame logging moved unchanged from
+   `godot/` into the new owner. Godot and `Age.Engine.Tests` now use project references, eliminating seven direct
+   test source links without changing public types, namespaces, behavior, or export configuration. Both solution
+   builds and runtime validation remain green.
+
 5. **Close repository-policy and storage gaps.** Add an explicit project license, third-party notices and
    checksums/provenance for committed binaries, consistent editor/build policy, a pinned .NET SDK, and a
    CI entry point built on the same validation driver. Remove the empty workspace-root `.git` directory and
@@ -1181,8 +1188,9 @@ layer's rendering diverges from ADV; save layout.
 
 ## 8. Immediate next step
 Begin step 4 of the **codebase consolidation** maintenance slice: make the build graph express source ownership
-without changing behavior. Introduce the production project boundary for platform-neutral frontend helpers now
-linked directly from `godot/` into `Age.Engine.Tests`, starting with the diagnostic/options helper cluster. Replace
-source links with project references while retaining both existing solution files and Godot export behavior.
+without changing behavior. Move the platform-neutral movie abstractions and runtime support—decoder interfaces,
+movie/audio runtime state, movie-surface registry, and RIFF sanitization—from `godot/` into
+`Age.Engine.Frontend` next. Replace their test source links while preserving the intentionally internal API through
+explicit friend-assembly access; leave FFmpeg interop/decoder ownership for the following slice.
 Concrete playthrough blockers may still preempt this bounded maintenance work; the consolidation effort does
 not replace Phase B gameplay validation or the open cross-platform gates.