ci(lint): skip prettier on push events — autofix handles main drift

[topcoder1]

Summary

• The loop being fixed: The lint reusable's prettier job ran on push:main events, scanning the full glob (no PR context for prettier_changed_only). Fleet repos with pre-existing markdown formatting drift (~20-70 files) fail every push:main lint run → prettier-autofix.yml fires, pushes a fix commit → triggers another push:main → repeat. webcrawl had 24 Lint failures out of 59 runs in a recent 7-day window from this loop alone.
• The fix: Added github.event_name == 'pull_request' to the prettier job's if: condition (combined with the existing run_prettier check). Prettier now only runs on PR events; push events skip it entirely.
• Backwards-compatible: Existing callers see prettier fire less often, never more. The prettier_changed_only input and all other inputs are unchanged. Actionlint and shellcheck remain on both event types.

Why this is safe

• Prettier on push:main can't gate anything — the merge already happened.
• prettier-autofix.yml already handles main-branch formatting drift on push:main — prettier's job is now just catching new bad files before they land (PR-only).
• The prettier_changed_only behavior on PRs is fully preserved.

What changes

Before: prettier job if: = format('{0}', inputs.run_prettier) != 'false' (fires on both PR and push events)

After: prettier job if: = github.event_name == 'pull_request' && format('{0}', inputs.run_prettier) != 'false' (fires on PR events only)

The header comment block is also updated to document this behavior and the rationale.

Fleet impact

~20 fleet repos use the lint reusable via topcoder1/ci-workflows. All benefit immediately after this merges — no caller changes needed. Estimated savings: ~$2-3/mo in CI minutes. More importantly, eliminates the Lint-failure alarm fatigue on main.

Test plan

• Self-test of lint.yml on pull_request trigger: prettier job runs and checks changed markdown files (unchanged behavior)
• Self-test of lint.yml on push:main trigger (after this PR merges): prettier job is skipped; actionlint still runs
• actionlint on the modified workflow: passes (verified locally with actionlint v1.7.12 — zero errors)
• Spot-check a fleet repo (e.g. webcrawl): after next push:main, confirm Lint no longer shows a prettier failure

Auto-merge rationale: Touches .github/workflows/** which is high-risk per claude-author-automerge.yml policy — manual click-merge required. Change is backwards-compatible (prettier fires less often, never more). Actionlint clean. No caller changes needed.

🤖 Generated with Claude Code

[github-actions]

Coverage Floor — mode: enforce

metric	value
measured	100.0%
floor (current)	99.0%
target	100.0%
last bumped	2026-05-12

[claude]

Flagged 1 issue: the prettier_changed_only input description (line ~68, not in diff) still says "Push events always scan the full glob" — but push events now skip prettier entirely. Should read something like "Not applicable on push events (prettier is skipped)." No logic bugs found; the github.event_name gate is correct and the reusable-workflow event-name behavior is handled.