fix(router): rmi snapshot image on PR merge so it isn't leaked to disk

[zbigniewsobiecki]

Summary

pr-merged previously called invalidateSnapshot(projectId, workItemId) — a registry-only operation. The Docker image lingered in storage, and the periodic 5-minute cleanup loop iterates registry entries only — so the now-orphaned image was leaked permanently, freed only by docker image prune -af or host disk pressure.

This is a primary contributor to the 2026-04-29 prod disk-fill incident that put Redis into MISCONF write-block.

Fix

• invalidateSnapshot(projectId, workItemId) now RETURNS the removed metadata (or undefined). Callers can docker rmi the underlying image; removing the registry entry without the image is the leak.
• New invalidateAndRemoveSnapshot(projectId, workItemId) in snapshot-cleanup.ts chains invalidateSnapshot + the existing removeSnapshotImage (which gracefully handles 404 / 409 and Sentry-captures unexpected docker errors).
• pr-merged.ts calls the new helper as fire-and-forget (void … .catch(logger.warn)) — preserves the non-blocking property of the original call site.
• removeSnapshotImage is now exported so the new helper reuses it without duplicating the rmi block.

Test plan

• tests/unit/router/snapshot-manager.test.ts — pins invalidateSnapshot returning metadata when an entry exists / undefined when not.
• tests/unit/router/snapshot-cleanup.test.ts — pins invalidateAndRemoveSnapshot calling docker.getImage().remove() on the registered image, no-op when nothing is registered, swallows 404 / 409.
• tests/unit/triggers/pr-merged.test.ts — mock target moved from snapshot-manager.invalidateSnapshot to snapshot-cleanup.invalidateAndRemoveSnapshot; existing assertions verify the helper is called with the right args on merged PRs and not on closed-but-not-merged or work-item-less PRs.
• All 8717 unit tests pass.
• npm run typecheck clean.
• npm run lint clean.

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 80.76923% with 5 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/triggers/github/pr-merged.ts	37.50%	5 Missing ⚠️

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