feat(render): Phase A8 — indoor visibility + streaming fixes batch

Lands the working A8 indoor-rendering and streaming fixes accumulated this
session. User has verified these visually to some degree (e.g. lifestone /
translucent meshes confirmed fine under the FrontFace flip; bridge / wall /
collision regressions confirmed fixed after travel); not every path has been
exhaustively gated. The cellar-flap defect remains OPEN and will be solved
the retail-faithful way via a dedicated brainstorm (see handoff docs).

Rendering core (reviewed, high confidence):
- EnvCellRenderer SSBO stride fix: upload packed Matrix4x4[] (64B) instead of
  the 80B CPU InstanceData struct the shader never expected — fixes the
  transform/texture "explosion" for any draw with >1 instance (cells that
  dedupe to a shared cellGeomId). Real root cause.
- WB-style global FrontFace(CW) + per-batch CullMode carried through the MDI
  layout (GroupKey + BuildIndirectArrays + DrawIndirectRange split into
  same-cull runs with absolute uDrawIDOffset per run).
- EntitySet partitioning (IndoorPass / OutdoorScenery / LiveDynamic) +
  WorldEntity.BuildingShellAnchorCellId so building shells scope to their
  dat-derived building cell instead of rendering everywhere.
- RenderOutsideInAcdream (look into buildings from outside) +
  CollectVisiblePortalBuildings frustum cull of portal bounds.
- Sky-when-inside-building + per-cell audit probe + GL-state probe.

Streaming / perf (test-covered; not independently code-reviewed this session):
- Near/far priority queues so near work wins over far; PromoteToNear carries
  full landblock + mesh data; LandblockEntriesWithoutAnimatedIndex avoids
  rebuilding the animated-lookup dict in the hot draw path. Fixes the
  bridge-not-appearing / missing-walls / broken-collision-after-travel
  regressions and improves post-transition FPS.

Tooling + docs:
- tools/A8CellAudit: offline dat cell/portal/building dumper (portals +
  buildings modes) — reproduces the cellar-flap investigation with no launch.
- docs/research cellar-flap root-cause + option-2 handoff (the didInsideStencil
  double-duty finding + the WB-recursive design decision + brainstorm prompt),
  entity-taxonomy, replan, issue-78 visibility investigation.

Diagnostics retained on purpose: ACDREAM_A8_DIAG_* gates, portal_stencil.vert
provisional pos.w clamp, and the probe families are kept (env-var gated, zero
cost when off) because the pending option-2 cellar-flap brainstorm needs them.
Strip in the option-2 ship commit.

Indoor branch stays behind ACDREAM_A8_INDOOR_BRANCH=1 (default off = pre-A8
visual). Build green; App tests + Core (streaming/dispatcher/loader) tests pass.

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

src/AcDream.App/Rendering/Shaders/portal_stencil.vert

@@ -1,6 +1,6 @@
 #version 430 core
 //
-// Phase A8 — portal stencil mark + far-depth punch.
+// Phase A8 - portal stencil mark + far-depth punch.
 //
 // Position is in WORLD space (pipeline transforms cell-local portal
 // polygon vertices through cell.WorldTransform on the CPU before
@@ -10,10 +10,16 @@ layout(location = 0) in vec3 aPosition;
 
 uniform mat4 uViewProjection;
 
-// Note: no pos.w clamp — coplanar-camera degenerate is accepted per spec.
-// If stencil artifacts appear when the camera straddles an exit portal plane,
-// re-introduce the clamp from WB's PortalStencil.vert.
 void main()
 {
-    gl_Position = uViewProjection * vec4(aPosition, 1.0);
+    vec4 pos = uViewProjection * vec4(aPosition, 1.0);
+
+    // Match WorldBuilder's PortalStencil.vert: keep portal polygons stable
+    // when the chase camera straddles an exit portal plane. Without this,
+    // near-zero clip W can explode the screen-space portal mask and let the
+    // Step 4 terrain pass punch into indoor floor/wall pixels for a frame.
+    if (abs(pos.w) < 0.001)
+        pos.w = pos.w < 0.0 ? -0.001 : 0.001;
+
+    gl_Position = pos;
 }