fix(regenerate): tolerate orphaned ACC baseline SHA in module detection

[GeekTrainer]

Description

The scheduled Regenerate learner branches (pull model) workflow has been failing on its daily cron. The detect step reads the last-processed ACC commit from course-build/.last-acc-sha and diffs it against the current ACC main HEAD. When the recorded baseline SHA no longer exists in the ACC repo (its history was rewritten / force-pushed, orphaning the commit), detect-affected-modules.mjs ran git diff <bad-object> and aborted with fatal: bad object ..., failing the run.

This makes detection resilient: an unreachable baseline is now treated the same as "no baseline" (a full regen) instead of crashing, so the pipeline self-heals on the next run (the regen PR advances .last-acc-sha to a valid commit on merge).

Related Issue

N/A

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to change)
• 📚 Documentation update
• 🧪 Test update
• 🔧 Refactor (no functional changes)

Affected Services

• web (Astro SSR + React)
• assets-svc (.NET 10)
• workforce-svc (Java 21 / Spring Boot 3)
• reporting-svc (Python FastAPI)
• notifications-svc (Python FastAPI)
• audit-svc (legacy Java 11 / Spring Boot 2.7)
• auth-svc (legacy Java 11 / Spring Boot 2.7)
• devcontainer / tooling / docs

Changes Made

• Add a commitExists(cwd, rev) reachability check (via git cat-file -e <rev>^{commit}) to detect-affected-modules.mjs.
• When the supplied --from baseline is not a reachable commit in the ACC repo, fall back to first-run semantics (full regen) instead of running git diff on a bad object. This is surfaced via a WARN log and a new baselineMissing field in the JSON output.
• Add a temp-repo integration selftest exercising both the valid-baseline (normal diff) and orphaned-baseline (fallback, no crash) paths.

Testing

• End-to-end (web): npm run test:e2e (Playwright) passes
• .NET: dotnet test in services/assets-svc passes
• Python: pytest in services/reporting-svc and/or services/notifications-svc passes
• Modern Java: mvn test in services/workforce-svc passes
• Currency-lagging Java: mvn test in services/audit-svc and/or services/auth-svc passes
• Manually verified the app runs (npm run dev or docker compose up --build) and the affected flow works at http://localhost:4321

Ran node course-build/scripts/selftest.mjs (the same suite invoked by validate-branches.yml); all checks pass, including the new baseline-fallback cases.

Checklist

• My change targets main (I have not hand-edited generated learner branches or promoted refs — see CONTRIBUTING.md)
• My code follows the project's coding standards for the affected language/stack
• My changes are focused on a single concern
• I have added or updated tests where it makes sense
• I have updated documentation (README, per-service READMEs, exercises.md) if needed
• I have written clear commit messages explaining what and why

Additional Notes

This resilience fix lands the code path, but the .last-acc-sha currently committed on main still points at the orphaned SHA. With this change, the next scheduled run no longer errors: it performs a full regen and opens a PR that advances .last-acc-sha to a valid commit. No manual baseline edit is required, though committing a valid SHA would also work as an immediate unblock.

[Copilot]

Pull request overview

Improves resilience of the course-build “detect affected modules” script used by the regenerate workflow by handling an invalid/orphaned baseline ACC SHA without crashing, and adds an integration selftest covering the fallback path.

Changes:

• Add commitExists() and baselineMissing output to treat an invalid --from baseline as first-run/full-regen semantics.
• Emit a warning when the baseline commit is missing/unresolvable instead of failing on git diff.
• Extend selftest.mjs with a temp-repo integration test covering both valid and missing-baseline behavior.

Show a summary per file

File	Description
course-build/scripts/detect-affected-modules.mjs	Adds baseline-existence guard and exposes baselineMissing to prevent git diff from crashing on bad baseline SHAs.
course-build/scripts/selftest.mjs	Adds an integration selftest that creates a temp git repo and verifies both normal diff and missing-baseline fallback behavior.

Review details

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Suppressed comments (1)

course-build/scripts/detect-affected-modules.mjs:88

• baselineMissing is computed using args.from.trim(), but git diff is run with the untrimmed args.from/args.to. If either value contains whitespace/newlines (e.g. read from a file), the baseline check can pass while git diff still fails with a bad revision. Consider normalizing from/to once and using those values for both the existence check and the diff.

  let files = [];
  if (!firstRun) {
    const out = git(args.acc, 'diff', '--name-only', `${args.from}`, `${args.to}`);
    files = out.split('\n').map(s => s.trim()).filter(Boolean);

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Lite