webxr: clear framebuffer to dark blue in headless mode

[gareth-morgan-nv]

Summary

• In headless mode the CloudXR frame blit is skipped while tracking/streaming continue, previously leaving stale/garbage framebuffer contents on screen.
• The connected-but-suppressed frame now clears to a fixed dark blue (0x00194d) every frame, so it's visually obvious the client is alive and running headless - matching what non-headless mode would otherwise be rendering.
• The "no session yet" / "not connected" skip branches are unchanged.

Test plan

• npx tsc --noEmit in deps/cloudxr/webxr_client (clean, no new errors introduced by this change)
• Manually verify: load the client with headless=true, confirm the canvas shows solid dark blue once the CloudXR session connects, instead of a blank/stale frame

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Summary by CodeRabbit

• Bug Fixes
  • Headless mode now displays a consistent dark-blue screen when rendering is suppressed.
  • Connected headless frames clear previous framebuffer contents, preventing stale visuals from remaining visible.

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📝 Walkthrough

Walkthrough

Headless mode now uses a dark-blue clear color. A React effect applies the color to the Three.js renderer when headless mode or the renderer changes. Connected headless frames clear the framebuffer with this color instead of retaining previous contents.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: 🔵 Low · up to 54a6b

This change makes connected headless frames display a dark-blue marker, but switching headless mode off can leave normal frames clearing dark blue. Restore the normal clear color before merge.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: clearing the framebuffer to dark blue in WebXR headless mode.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
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Actionable comments posted: 1

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Inline comments:
In `@deps/cloudxr/webxr_client/helpers/react/CloudXRComponent.tsx`:
- Around line 203-205: Update the renderer configuration in CloudXRComponent so
the effect handling headless changes sets HEADLESS_CLEAR_COLOR when headless is
true and restores the normal clear color when headless becomes false without
remounting. Ensure later threeRenderer.clear() calls use the appropriate color
for the current mode.

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• deps/cloudxr/webxr_client/helpers/react/CloudXRComponent.tsx

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[gareth-morgan-nv]

Fixed in 4a75af6: captured the renderer's original clear color/alpha once and restore it when headless toggles back to false, so later threeRenderer.clear() calls in the non-headless path no longer stay stuck on the dark blue marker color.