captures: readable player-view captures with a coverage gate (L69); R36 native-generator survey

- Capture exports now cover a 90-degree player frustum (radius 3, LOD 0-8, overlap patches);
  a 17x9 ray coverage probe aborts before rendering if tiles are missing (truncated-mesh
  control: 480 uncovered samples, rejected). Clear colour is sky blue, so un-meshed space can't
  pass as dark rock. 16 views of the owner's four-strate plan.
- Explore commandlet: finite XYZ spawn override for traces (Source/, Linux-compiled).
- In-engine four-strate trace NOT obtained: the engine-generated plan fails passage validation
  at a solid centerline voxel (~(-43,-34.5,-448.5) m) while the headless owner_world.json
  plan passes. Engine and headless plans diverge.
- R36 (read-only): order TN -> VS -> FI for native migration; native FI is reachable from the
  adapter but not selected in the owner run, cause unknown.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Source/LinuxOffscreenCapture.cpp

@@ -794,7 +794,9 @@ void main()
         glEnableVertexAttribArray(5);glVertexAttribPointer(5,4,GL_FLOAT,GL_FALSE,sizeof(FVertex),
             reinterpret_cast<void*>(offsetof(FVertex,Material)));
         glViewport(0,0,Width,Height);glDisable(GL_CULL_FACE);glEnable(GL_DEPTH_TEST);
-        glDepthFunc(GL_LEQUAL);glClearColor(0.035f,0.055f,0.075f,1.0f);
+        // A covered empty ray represents open air. Keep it visibly blue so it cannot
+        // be mistaken for the old near-black result from a scene that lacked tiles.
+        glDepthFunc(GL_LEQUAL);glClearColor(0.30f,0.48f,0.62f,1.0f);
         glClearDepthf(1.0f);glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
         glUseProgram(Program);
         glUniform1f(glGetUniformLocation(Program,"uTanHalfHorizontal"),static_cast<float>(TanHalfHorizontal));