vcr-debugger

name: vcr-debugger description: Diagnose and fix VCR manifest/render failures. Use when vcr check, vcr lint, vcr preview, vcr render-frame, or vcr build fail; when output is blank/incorrect; or when determinism and backend behavior must be investigated.

VCR Debugger

Debug VCR failures quickly with a deterministic triage sequence.

Triage Sequence

1. Validate manifest shape and references:
   • vcr check <scene>.vcr
   • vcr lint <scene>.vcr
2. Inspect frame-level state:
   • vcr dump <scene>.vcr --frame <n>
3. Reproduce with a single frame:
   • vcr render-frame <scene>.vcr --frame <n> -o renders/debug_f<n>.png
4. Verify runtime/dependency health:
   • vcr doctor
5. If determinism is in question:
   • vcr determinism-report <scene>.vcr --frame <n> --json

Debug Heuristics

• Start with check before any expensive render.
• Prefer minimal frame repro (render-frame) over full build during debugging.
• Isolate params and disable optional complexity (post/shaders) when narrowing root cause.
• Confirm backend assumptions for GPU-only features.

Common Root Causes

• Schema/key typos (deny_unknown_fields).
• Missing required environment fields.
• Invalid expression functions/variables.
• Invalid or out-of-scope asset paths.
• GPU-only features executed on software backend.

Success Criteria

• Reproducible root cause identified.
• Error state removed (check passes).
• Target frame or preview matches expected visual behavior.

Failure Handling

• If failing command output is unclear, rerun on reduced scene complexity.
• If render mismatch persists, compare with a known-good minimal manifest.
• If backend-specific behavior diverges, document backend + platform in repro notes.