fix: prevent camera reset when toggling pathtracing with CurveAttachment

[PythonFZ]

Known issue:

1. attach camera to curve
2. toggle pathtracing on
3. toggle it off
4. detach camera from curve
   Now positions is 0,0,0 and the camera only becomes responsive again, when setting positions manually.
   Also webgl context loss on pathtracing changes.

When pathtracing was toggled, cameras using CurveAttachment positions would reset to the first point of the curve instead of maintaining their current position.

Root cause: PathTracingRenderer returned different component types depending on pathtracing state (Fragment vs Pathtracer), causing React to remount children. When Camera remounted, its state reinitialized to the first curve point instead of the resolved CurveAttachment position.

Changes:

• PathTracingRenderer: Always render Pathtracer with enabled prop to maintain stable React tree structure and prevent child remounting
• Canvas: Remove pathtracingEnabled from Canvas key (unnecessary)
• Curve: Return empty group instead of null when pathtracing enabled to keep curveRef registered for CurveAttachment resolution

Summary by CodeRabbit

• Bug Fixes

  • Prevented unnecessary remounts when toggling path tracing and ensured 3D attachments remain resolvable during path tracing.
  • Pathtracer now correctly respects the enabled setting and omits related updaters when disabled.

• Improvements

  • Smoother, more stable camera positioning and interpolation, including curve-based interpolation for transitions and loading.

• Refactor

  • Unified and simplified camera and rendering logic for more consistent behavior.

• Chore

  • Adjusted screenshot membership/permission check on the server side.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

Memoized camera position resolution added via a new resolvePosition utility and integrated into Canvas and Camera; PathTracing rendering now respects the enabled flag and conditionally mounts updater/capture/environment; Curve components remain mounted during pathtracing; server-side membership check changed from RoomKeys.members() to RoomKeys.users().

Changes

Cohort / File(s)	Summary
Camera utilities & resolution app/src/utils/cameraUtils.ts	Added interpolateCurvePosition and resolvePosition to resolve direct coordinates or CurveAttachment references from geometries.
Camera component refactor app/src/components/three/Camera.tsx	Replaced inline position/target resolution with resolveToVector3 that uses resolvePosition/curve interpolation; unified projection updates and simplified camera-type handling.
Canvas position memoization app/src/components/Canvas.tsx	Introduced useMemo + resolvePosition to compute cameraPosition from sessionCameraData.position (default [0,0,10]) before early returns.
Pathtracing gating & renderer app/src/components/PathTracingRenderer.tsx	Use actual enabled prop for Pathtracer; render PathtracingUpdater, PathtracingCaptureProvider, and Environment only when enabled (and environment preset not "none").
Curve mounting behavior app/src/components/three/Curve.tsx	When pathtracing is enabled, mount an empty <group /> instead of returning null to preserve curveRef registration for attachments.
Server session route change src/zndraw/app/session_routes.py	Switched membership verification from RoomKeys.members() to RoomKeys.users() in request_screenshot.

Sequence Diagram(s)

(omitted — changes are internal/conditional rendering and utilities that do not introduce a new multi-component sequential workflow warranting a diagram)

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• Feat/screenshot system improvements #864: Modifies the screenshot/capture and pathtracing subsystems (frontend capture/providers and backend screenshot endpoints), likely related to these rendering and capture changes.

Poem

🐰
I hop through vectors, soft and spry,
I memoize the camera sky.
Curves stay planted, waiting near,
Pathtraces whisper, "Mount, not clear."
A rabbit cheers — the render's here!

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main issue being fixed: preventing camera reset when toggling pathtracing with CurveAttachment, which is the root cause addressed across multiple component changes.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

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[coderabbitai]

Actionable comments posted: 0

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

app/src/components/PathTracingRenderer.tsx (1)

45-48: Remove Fragment fallback to maintain stable component tree and prevent unnecessary remounts.

Lines 24-25 return a Fragment when enabled is false, which changes the wrapper type based on the enabled state. This violates the pattern already established on line 8 (which renders <Pathtracer enabled={false}> for loading state) and can cause remounts when the enabled prop changes. Always render Pathtracer and let the enabled prop control behavior, as shown in the suggested fix.

Suggested fix

-	// Pass through if not enabled
-	if (!enabled) {
-		return <>{children}</>;
-	}
-
-	return (
-		<Pathtracer
-			minSamples={min_samples}
-			samples={samples}
-			bounces={bounces}
-			tiles={tiles}
-			enabled={enabled}
-		>
+	return (
+		<Pathtracer
+			minSamples={min_samples}
+			samples={samples}
+			bounces={bounces}
+			tiles={tiles}
+			enabled={enabled}
+		>
 			{enabled && <PathtracingUpdater settings={settings} />}
 			{enabled && <PathtracingCaptureProvider />}
 			{enabled && environment_preset !== "none" && (
 				<Environment
 					preset={environment_preset}
 					background={environment_background}
 					backgroundBlurriness={environment_blur}
 					environmentIntensity={environment_intensity}
 				/>
 			)}
 			{children}
 		</Pathtracer>
 	);

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 79.79%. Comparing base (731ce39) to head (9f9c252).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/zndraw/app/session_routes.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #866      +/-   ##
==========================================
- Coverage   79.81%   79.79%   -0.02%     
==========================================
  Files         165      165              
  Lines       20213    20213              
==========================================
- Hits        16133    16129       -4     
- Misses       4080     4084       +4     

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