classifyFile: order code/config/test extension checks before the docs/ prefix fallback (latent carry-forward soundness)

[mfittko]

Problem

classifyFile() in packages/core/src/analysis/diff-analyzer.mjs returns docs for any path under docs/ because the docs/ prefix check precedes the code/.mjs and config/.json extension checks. A code or config file hosted under docs/ (e.g. docs/example.mjs imported by a test, docs/fixture.json consumed at runtime) classifies as docs.

Two fail-closed consumers depend on this classifier and would then treat such a file as prose:

• Angle carry-forward (resolveAngleCarryForward, perf(gate): iterative small-fix convergence re-fans all angles + Copilot re-flags resolved nits #1308): a doc-only delta carries a clean code-angle verdict forward — a docs/-hosted code file could carry a code angle over an unreviewed code change.
• Copilot round-cap convergence (resolveConvergenceCarryForward, feat(gate): wire the Copilot loop to consume convergence carry-forward (AC2 follow-up to #1308) #1326): a post-convergence docs/-hosted code/config change could be suppressed from a fresh Copilot round.

Status: latent, not active

docs/ currently holds only .md/.html/.css prose + presentation assets — no .mjs/.json/.yml. So no code escapes today. The analogous "load-bearing .md" case (SKILL.md etc.) is intentionally docs (Copilot does not code-review prose) and is correct by design. This is a defense-in-depth hardening against a future docs/-hosted script/config being silently carried forward.

Acceptance criteria

• classifyFile() classifies a path by known code/config/test extension before the docs/ (and any other directory-prefix) fallback, so a docs/example.mjs → code and docs/fixture.json → config, while docs/foo.md stays docs.
• Unit tests cover a code/config/test-extension file under docs/ classifying by extension, and a .md/.html/.css under docs/ still classifying as docs.
• Both carry-forward consumers (resolveAngleCarryForward, resolveConvergenceCarryForward) inherit the corrected classification (a docs/-hosted code/config delta now re-runs the angle / re-opens the round).
• npm run verify green.

Non-goals

Changing the docs/-hosted prose (.md/SKILL.md) → docs behavior. Reworking the surface map or the carry-forward decision logic (only the file-kind classifier's ordering).

Found during the #1329 pre-approval deep review.