feat(gastown+web): slingExistingPr + BeadPanel babysit badge (chunks 0+4)

[jrf0110]

Summary

Implements chunks 0 and 4 of the "Babysit existing PR" feature:

Chunk 0 — Town DO slingExistingPr method + review-queue refactor:

• Refactored submitToReviewQueue to extract createMergeRequestBeadCore private helper (public signature unchanged, no caller changes)
• Added submitExternalPrToReviewQueue function that creates merge_request + review_metadata rows with gt:babysit label, no tracks edge, and babysit_started activity event
• Added Town.do.ts::slingExistingPr method with repo validation, open-state check, PR metadata fetch, and title/body defaults
• Extended checkPRStatus return shape with head_branch, base_branch, head_sha, title (existing callers unchanged)
• Added parsePrUrlForRepoMatch utility for repo-match validation

Chunk 4 — BeadPanel babysit badge + metadata surfacing:

• "Babysat external PR" badge in BeadPanel header when gt:babysit label present
• Head SHA (abbreviated) and force-push status in metadata panel
• Extracted eventDescription to separate module for testability
• Added event formatters for babysit event types: babysit_started, pr_feedback_detected, pr_conflict_detected, pr_auto_merge, pr_status_changed
• Added babysit_started event type to bead-events table

Verification

• pnpm --filter cloudflare-gastown test — all 19 new unit tests pass
• babysit-ui.test.ts — 9 event description tests pass (imports from extracted event-description.ts, no runtime component import)
• Manual: verified BeadPanel renders babysit badge and metadata for gt:babysit labeled beads

Visual Changes

BeadPanel now shows "Babysat external PR" badge, head SHA, and force-push status for babysat beads. Event timeline renders babysit-specific event types with appropriate icons and descriptions.

Reviewer Notes

• The createMergeRequestBeadCore refactor is intentionally minimal — single private helper, public API unchanged
• checkPRStatus extension is backward-compatible: new fields are optional
• Chunk 4 was included because it's tightly coupled to the chunk 0 metadata/label schema and could run in parallel with chunks 2-3

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

All 5 issues from the previous review have been addressed in commit d1d866b34; no new issues were found in the incremental diff.

Previously Reported Issues — All Resolved

File	Issue	Status
services/gastown/src/util/platform-pr.util.ts	lastSlash > 0 silently dropped root-level GitLab projects	✅ Fixed (>= 0 + fallback return)
apps/web/src/components/gastown/ActivityFeed.tsx	Redundant export { eventDescription } barrel re-export	✅ Removed
services/gastown/src/dos/Town.do.ts	Planning artifact "wired in chunk 1" in user-facing warning string	✅ Removed
apps/web/src/components/gastown/event-description.ts	as string | undefined casts on metadata fields bypassed runtime type safety	✅ Replaced with typeof guards
services/gastown/src/dos/town/review-queue.ts	No deduplication guard in submitExternalPrToReviewQueue	✅ Added dedup query + warning return

Files Reviewed (6 files, incremental)

• apps/web/src/components/gastown/ActivityFeed.tsx — previously flagged issue resolved
• apps/web/src/components/gastown/event-description.ts — previously flagged issue resolved
• services/gastown/src/dos/Town.do.ts — previously flagged issue resolved
• services/gastown/src/dos/town/review-queue.ts — previously flagged issue resolved
• services/gastown/src/util/platform-pr.util.ts — previously flagged issue resolved
• services/gastown/test/unit/sling-existing-pr.test.ts — new dedup test and root-level GitLab test added

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_{Reviewed by claude-4.6-sonnet-20260217 · 1,006,657 tokens}

_{Review guidance: REVIEW.md from base branch convoy/babysit-existing-pr-feature-re-staged/254a4b7e/head}