fix(retro): language-agnostic test detection + anti-fabrication guard

[SholtoMc]

Problem

While verifying a generated weekly retro against git history, two headline metrics turned out to be fabricated:

• "Bootstrap commit #2203 — 5,165 files · 1.4M lines · 1,455 test files." The cited commit was actually a 2-file, 187-line docs PR. No bootstrap had occurred (the repo was 8+ months / 1,200+ commits old).
• "0 new tests added." In reality ~28 test files were added that week.

Root cause

The /retro Step-1 data collection counts tests with JS/TS-only patterns:

# "Test files changed in window"
git log ... --name-only | grep -E '\.(test|spec)\.' | sort -u | wc -l

\.(test|spec)\. only matches foo.test.ts / foo.spec.js. It returns 0 for:

• Python test_*.py / *_test.py
• Terraform *.tftest.hcl
• Bats *.bats
• path-based tests/…

The total-test find (command 10) likewise missed the test_*.py prefix convention. So the generator saw "N total tests exist" but "0 added this period," and reconciled that contradiction by inventing a non-existent "bootstrap commit" with made-up file/LOC figures — there was no guard forcing per-commit numbers to come from the commit itself.

Fix

• Commands 10 / 12 / 13 now use a language-agnostic test pattern (Python / JS-TS / Ruby / Terraform / Bats / path-based), exclude vendored dirs, and split tests ADDED (--diff-filter=A) from TOUCHED. Command 10 uses git ls-files (respects .gitignore).
• New Step 1.5 "plausibility guard": per-commit figures must come from git show --shortstat <hash>; never invent a "bootstrap/foundation/initial-import" narrative; reconcile count contradictions by re-checking command 12, not by narrating an unverified event.
• Applied to both retro/SKILL.md.tmpl (source) and retro/SKILL.md (runtime).
• test/regression-retro-test-detection.test.ts locks in both invariants (21 tests).

Verification

On the affected repo's window the patched commands return 28 tests added / 47 touched (was 0). bun test test/regression-retro-test-detection.test.ts → 21/21 pass; existing regression-1624-retro-stale-base.test.ts → 13/13 pass.

🤖 Generated with Claude Code

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[jbetala7]

Overlap heads-up: this shares its command-10 change with the older, issue-linked #2013 (Closes #1999). Both rewrite the same glob at retro/SKILL.md:1000 and the mirrored line in retro/SKILL.md.tmpl — JS/TS-only find … | grep -v node_modules → polyglot pattern + vendored-dir exclusion — so whichever merges second will conflict on those exact lines.

The deltas here are real and worth keeping: this PR additionally fixes commands 12/13 (retro/SKILL.md:1009, still grep -E '\.(test|spec)\.' on main, which #2013 doesn't touch) and adds the Step 1.5 plausibility guard + regression test — the headline anti-fabrication value. #2013 is narrower but carries the issue link.

Suggestion: since this is a superset, consider adding Closes #1999 and crediting #2013, so the maintainer can land this one and close the narrow PR without dropping the issue. If #2013 lands first instead, this just needs a rebase to drop the duplicate command-10 / vendored-exclusion hunk.