feat: add REACT_DOCTOR_NO_SCAN_CACHE for granular cache opt-out

[skoshx]

Problem

React Doctor 0.9.13's whole-scan result cache computes a repository identity using git status --porcelain=v1 -z --untracked-files=all and the contents of dirty files (buildScanResultCacheKey → resolveRepositoryCacheIdentity → buildWorktreeFingerprint). Vite Task automatically records child-process filesystem accesses as inputs. Running Doctor inside a cached package task therefore makes unrelated repository changes invalidate that package's verdict.

The outer task cache already replays the complete verdict. Doctor's per-file lint and sidecar caches remain useful when a changed package actually runs. REACT_DOCTOR_NO_CACHE switches all three off, so it is too broad here.

Solution

Add REACT_DOCTOR_NO_SCAN_CACHE, with the same truthy-value convention as REACT_DOCTOR_NO_CACHE, returning null from buildScanResultCacheKey before isGitIdentityTrustworthy or repository fingerprint collection. Preserve normal behavior when the flag is absent, and leave per-file and sidecar caches enabled.

Implementation

• Added isScanCacheDisabled() function that checks both REACT_DOCTOR_NO_CACHE (global) and REACT_DOCTOR_NO_SCAN_CACHE (granular)
• Modified buildScanResultCacheKey to use the new granular check early, before any Git operations
• Per-file and sidecar caches remain unaffected - they continue to use their own Reference defaults
• Updated documentation in comments to reflect the new flag

Testing

• ✅ Added unit tests for the new environment variable behavior
• ✅ Added test to verify git status is not called when REACT_DOCTOR_NO_SCAN_CACHE is set
• ✅ Added test to verify REACT_DOCTOR_NO_CACHE (global) still overrides REACT_DOCTOR_NO_SCAN_CACHE=false
• ✅ All existing scan-result-cache tests pass (31 tests)
• ✅ Typecheck passes
• ✅ Lint passes
• ✅ Added patch-level changeset

Parity Analysis

Parity testing is not applicable for this change because:

• This is a cache control feature, not a rule or diagnostic change
• The diagnostics output is identical whether the cache is enabled or disabled
• The feature only affects when results are cached, not what results are produced
• When REACT_DOCTOR_NO_SCAN_CACHE is unset (the default), behavior is identical to before

Closes #1804

  

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commit: f18001b

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit f18001b.}

[github-actions]

Interactive terminal E2E

Terminal Control verified the built CLI at f18001b in a real PTY:

• selected a project interactively and observed Scanning... before the three-second Git delay completed
• waited for the clean result and exercised the compact report
• opened copy context and the GitHub Actions confirmation, then cancelled safely

Download the edited MP4 and PNG evidence