phase(N.5): retirement amendment — InstancedMeshRenderer + StaticMeshRenderer + WbFoundationFlag deleted

Final cross-cutting review of N.5 found that Task 15's deletion of
mesh_instanced.vert/.frag left InstancedMeshRenderer orphaned —
ACDREAM_USE_WB_FOUNDATION=0 silently rendered terrain+sky only with
no entities. The SHIP commit's "[x] ACDREAM_USE_WB_FOUNDATION=0 still
works" claim was inaccurate.

Resolution: formal retirement of the legacy renderer path within N.5
instead of deferring to N.6.

Deleted:
- src/AcDream.App/Rendering/InstancedMeshRenderer.cs
- src/AcDream.App/Rendering/StaticMeshRenderer.cs
- src/AcDream.App/Rendering/Wb/WbFoundationFlag.cs

GameWindow simplified — capability detection is unconditional, missing
bindless throws NotSupportedException with a clear message at startup.
WbDrawDispatcher + mesh_modern shader load are mandatory after init.
No escape hatch.

GpuWorldState simplified — WbFoundationFlag.IsEnabled guards on
AddLandblock/RemoveLandblock removed; adapter calls are unconditional
when the adapter is non-null.

PendingSpawnIntegrationTests updated — WbFoundationFlag.ForTestsOnly_ForceEnable
static ctor removed (flag is gone; adapter calls are unconditional).

The ApplyLoadedTerrain physics-data loop was also simplified: the
EnsureUploaded sub-loop that fed InstancedMeshRenderer is gone;
_pendingCellMeshes is now explicitly cleared to prevent unbounded
accumulation (the worker thread still populates it, but WB handles
EnvCell geometry through its own pipeline).

Spec §2 Decision 5 + §10 Out-of-Scope updated. Plan ship-amendment
section added. Roadmap updated (N.5 ships with retirement; N.6 scope
narrowed to perf-only). CLAUDE.md "WB integration cribs" updated.
Perf baseline doc updated. WbDrawDispatcher class summary docstring
corrected to describe the as-shipped SSBO + multi-draw-indirect path.
ISSUES.md #51 updated (terrain not in N.5 scope; deferred to N.7).

Bindless support is now a hard requirement. Modern desktop GPUs
universally expose GL_ARB_bindless_texture + GL_ARB_shader_draw_parameters;
if a user hits the NotSupportedException, that's a real bug report
worth investigating, not a silent fallback.

Build: 0 errors, 0 warnings. Tests: 71/71 (Wb+MatrixComposition+TextureCacheBindless filter).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -55,9 +55,11 @@ ourselves".
   `EntitySpawnAdapter.cs` — bridge spawn lifecycle to WB ref-counts.
   Atlas tier (procedural) goes via Landblock; per-instance tier
   (server-spawned, palette/texture overrides) goes via Entity.
-- `WbFoundationFlag` is default-on. `ACDREAM_USE_WB_FOUNDATION=0`
-  falls back to legacy `InstancedMeshRenderer` (kept as escape hatch
-  until N.6 fully retires it).
+- **Modern path is mandatory as of N.5 ship amendment (2026-05-08).**
+  `WbFoundationFlag`, `InstancedMeshRenderer`, and `StaticMeshRenderer`
+  are deleted. Missing `GL_ARB_bindless_texture` or
+  `GL_ARB_shader_draw_parameters` throws `NotSupportedException` at
+  startup. There is no legacy fallback.
 - **WB's modern rendering path** (GL 4.3 + bindless) packs every mesh
   into a single global VAO/VBO/IBO. Each batch references its slice
   via `FirstIndex` (offset into IBO) + `BaseVertex` (offset into VBO).
@@ -500,21 +502,25 @@ acdream's plan lives in two files committed to the repo:
   acceptance criteria. Do not drift from the spec without explicit user
   approval.
 
-**Currently in flight: Phase N.6 — Retire legacy renderers + perf polish.**
+**Currently in flight: Phase N.6 — Perf polish.**
 Roadmap entry at [`docs/plans/2026-04-11-roadmap.md`](docs/plans/2026-04-11-roadmap.md).
-Builds on N.5. Retires `InstancedMeshRenderer` + `StaticMeshRenderer` entirely.
-Optional candidates: WB atlas adoption, persistent-mapped buffers, GPU-side
-culling via compute pre-pass, GL_TIME_ELAPSED query double-buffering, direct
-N.4 vs N.5 perf measurement. Plan + spec written when work begins.
+Builds on N.5. Legacy renderers (`InstancedMeshRenderer`, `StaticMeshRenderer`,
+`WbFoundationFlag`) were retired in the N.5 ship amendment — N.6 scope is
+perf-only: WB atlas adoption, persistent-mapped buffers, GPU-side culling,
+GL_TIME_ELAPSED query double-buffering, direct N.4 vs N.5 perf measurement,
+legacy `Texture2D`/`sampler2D` TextureCache path retirement (Sky/Terrain/Debug).
+Plan + spec written when work begins.
 
-**Phase N.5 (Modern Rendering Path) shipped 2026-05-08.** `WbDrawDispatcher`
+**Phase N.5 (Modern Rendering Path) shipped + amended 2026-05-08.** `WbDrawDispatcher`
 on bindless textures + `glMultiDrawElementsIndirect`. CPU dispatcher 1.23ms/frame
-at Holtburg (~810 fps). Plan archived at
+at Holtburg (~810 fps). **Ship amendment:** `InstancedMeshRenderer`,
+`StaticMeshRenderer`, `WbFoundationFlag` deleted in same phase — modern path is
+mandatory; missing bindless throws at startup. Plan archived at
 [`docs/superpowers/plans/2026-05-08-phase-n5-modern-rendering.md`](docs/superpowers/plans/2026-05-08-phase-n5-modern-rendering.md).
 
 **Phase N.4 (Rendering Pipeline Foundation) shipped 2026-05-08.** WB's
-`ObjectMeshManager` is integrated and is the default rendering path
-behind `ACDREAM_USE_WB_FOUNDATION` (default-on). Plan archived at
+`ObjectMeshManager` is integrated and is the production rendering path
+(mandatory as of N.5 ship amendment). Plan archived at
 [`docs/superpowers/plans/2026-05-08-phase-n4-rendering-foundation.md`](docs/superpowers/plans/2026-05-08-phase-n4-rendering-foundation.md).
 
 **Rules:**