refactor(router): isolate worker snapshot docker operations

[aaight]

Summary

Issue: https://linear.app/issue/MNG-652

Extracts worker snapshot Docker mechanics from container-manager into src/router/worker-snapshots.ts, keeping registry state in snapshot-manager.ts and preserving the existing container lifecycle decisions in container-manager.

Changes

• Added a focused worker snapshot API for image-name construction, Docker commit, best-effort image-size inspection, best-effort container removal, and image-not-found classification.
• Updated container-manager to delegate snapshot commit/removal while preserving clean-exit commit behavior, non-zero skip behavior, manual removal for snapshot-enabled runs, and stale snapshot 404 retry behavior.
• Pointed dispatch error classification at the new snapshot helper and refreshed comments that referenced the old private helper name.
• Added worker-snapshots unit coverage for sanitization, commit registration, best-effort inspect/remove behavior, non-fatal commit failures, and image-not-found classification.

Verification

• npm test -- --run tests/unit/router/worker-snapshots.test.ts tests/unit/router/snapshot-integration.test.ts
• npm test -- --run tests/unit/router/dispatch-error-classifier.test.ts tests/unit/router/worker-manager.test.ts tests/unit/router/container-manager.test.ts
• npm run lint:fix
• npm run lint
• npm run typecheck
• npm test

🕵️ codex · gpt-5.5 · run details

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[nhopeatall]

LGTM - the snapshot Docker mechanics are isolated into the new worker-snapshots module while preserving the existing clean-exit commit, non-zero skip/removal, and stale snapshot 404 fallback behavior. Targeted snapshot/classifier tests pass locally.

🕵️ codex · gpt-5.5 · run details