feat(triggers): add silent-merge and branch-sync trigger words

[aseemann]

Summary

Sharpens the skill description so it triggers on a raw branch-to-branch sync (e.g. merging master into an integration branch) — not only PR-shaped merges.

Came from

/retro session on 2026-08-26.
Finding: B15 (skill trigger-coverage gap) — the assistant merged a 90-commit-diverged master into an integration branch and never invoked this skill.
Learning-Id: retro-20260826-git-workflow-merge-trigger

• Symptom: Git auto-merged several files "cleanly" (no conflict markers) while silently dropping content both sides had added independently (app/composer.json's config.platform.php, two site-config YAML files' baseVariants entries). The assistant spent ~40+ ad hoc tool calls manually reconstructing base/ours/theirs diffs per file to catch this.
• Cause: This skill's references/advanced-git.md already documents this exact failure mode ("A merge resolved in favour of the branch silently reverts upstream work") with a ready detection script (git merge-file -p --diff3 against base/ours/theirs/result), and ships two evals for it (detect_upstream_work_dropped_by_merge, clean_merge_can_drop_entries — whose prompt even names composer.json). The description never surfaced it because it reads as PR-centric ("merging PRs", "handling merge conflicts"), not "verify a completed merge" or "sync a long-diverged branch."
• Required behavior: The skill should trigger for "did my merge drop anything", "sync integration from master", and similar branch-sync/merge-verification phrasing, not only PR review language.
• Verification: Existing evals detect_upstream_work_dropped_by_merge and clean_merge_can_drop_entries already cover the content; this PR only widens the trigger surface, verified via skill-repo's validate-skill.sh (0 errors; description-length warning already pre-existing before this change, 657→752 chars).

Change

One-line edit to skills/git-workflow/SKILL.md frontmatter description: added "verifying a merge didn't silently drop changes, syncing a long-diverged branch (e.g. master into integration)" between the existing "handling merge conflicts" and "rebasing a long-lived branch" clauses.

Test plan

• skill-repo's validate-skill.sh run against the repo root: 0 errors, same warning count as before the change
• Confirmed no existing eval needed changes (content already covered)

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[CybotTM]

Reviewed the description delta against the retro finding it encodes: the two inserted clauses name exactly the phrasings the B15 gap missed (merge-verification and branch-sync language), the covering evals already exist (detect_upstream_work_dropped_by_merge, clean_merge_can_drop_entries), and the 752-char description stays within the skill spec's limit — the validator's length warning predates this change. Copilot review is out of monthly quota, so this stands as the review. One mechanical note before merging: the branch is behind main and the classic protection requires up-to-date branches — rebase locally with signing (gh pr update-branch rewrites the head unsigned and trips the signature rule, see #226).

[CybotTM]

Re-approving head 0e30338: identical content to my reviewed ef777c2 — a signed rebase onto current main (author unchanged), no diff delta. Copilot review remains out of monthly quota.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud