feat(gastown): tRPC + HTTP for babysit PR (chunk 1)

[jrf0110]

Summary

Chunk 1 of 6 for the "Babysit existing PR" feature. Builds on chunk 0 (already merged) which added slingExistingPr and submitExternalPrToReviewQueue.

• gastown.babysitPr tRPC mutation — validates input, verifies rig ownership, calls townStub.slingExistingPr with sourceAgentId: 'system'
• gastown.previewPr tRPC query — returns PR metadata (state, branches, SHA, title) without side effects. Returns repo_matches: false on repo mismatch instead of throwing, so the UI can render a clear error
• POST /api/mayor/:townId/tools/babysit-pr — mayor-tools HTTP route, mirrors existing MayorSlingBody pattern, calls slingExistingPr with sourceAgentId: 'mayor'
• Refinery bypass — dispatch_agent in actions.ts returns null for merge_request beads with metadata.babysit === true, preventing refinery dispatch
• Reconciler fast-track — new block in reconcileMergeRequests fast-tracks open MR beads with metadata.babysit=true to in_progress regardless of the rig's code_review config. Also excludes babysat beads from refinery dispatch queries.

Verification

• All 60 unit tests pass (36 new in babysit-pr.test.ts, 24 existing in sling-existing-pr.test.ts)
• Pre-existing client.test.ts JWT token failures are unrelated to this change

Visual Changes

N/A

Reviewer Notes

• The previewPr method on TownDO reuses the same repo-validation and SCM-fetch logic as slingExistingPr (both call checkPRStatus). No duplicate code paths.
• The reconciler babysit fast-track runs independently of the code_review: false fast-track, so babysat beads on rigs with code_review: true are handled correctly.
• The dispatch_agent null return for babysat beads means the reconciler's transition_bead action is the sole path that moves them to in_progress, which then triggers poll_pr on the next alarm tick.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

The merge conflict markers in process-manager.test.ts (the sole CRITICAL issue from the previous review) have been resolved; no new issues were introduced.

Resolved Issues

• services/gastown/container/src/process-manager.test.ts — merge conflict markers removed ✓
• services/gastown/test/unit/sling-existing-pr.test.ts — duplicate file was removed in a prior commit ✓

Files Reviewed (14 files)

• services/gastown/container/src/process-manager.test.ts — resolved ✓
• services/gastown/src/db/tables/bead-events.table.ts
• services/gastown/src/dos/Town.do.ts
• services/gastown/src/dos/town/actions.ts
• services/gastown/src/dos/town/reconciler.ts
• services/gastown/src/dos/town/review-queue.ts
• services/gastown/src/dos/town/town-scm.ts
• services/gastown/src/gastown.worker.ts
• services/gastown/src/handlers/mayor-tools.handler.ts
• services/gastown/src/trpc/router.ts
• services/gastown/src/trpc/schemas.ts
• services/gastown/src/util/platform-pr.util.ts
• services/gastown/test/unit/babysit-pr.test.ts
• services/gastown/test/unit/sling-existing-pr.test.ts — removed ✓

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_{Reviewed by claude-sonnet-4.6 · 192,151 tokens}

_{Review guidance: REVIEW.md from base branch gastown-staging}