[Fix] Background service failures can surface as unhandled rejections

[zoomote]

​Created by Roomote. Follow up by mentioning @roomote, in the web UI, or in Discord.

What changed

• Expanded the type-aware @typescript-eslint/no-floating-promises ratchet to services/**/*.ts and resolved all six existing findings.
• Added explicit failure handling for detached code-index startup and MCP settings watcher initialization.
• Replaced scanner cleanup finally() chains with success/failure cleanup handlers that cannot create an unobserved rejected promise.
• Replaced test-only Promise scheduling with queueMicrotask and added focused startup-rejection and threshold-batch cleanup coverage.

Why this change was made

Long-running indexing and MCP watcher setup are intentionally started in the background, but their rejected promises were not owned by a terminal handler. Scanner cleanup also discarded the promise returned by finally(), which can reject whenever its source rejects.

Impact

Background service failures are now logged instead of surfacing as unhandled rejections, batch cleanup still runs on success and failure, and future floating promises in services/** fail lint. Background execution timing remains unchanged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[zoomote]

Addressed both lines from Codecov’s initial report with a threshold-one scanner test that executes the in-loop batch cleanup path. Local coverage confirms the reported lines are now exercised; the full lint, type-check, and test suites pass.

Pushed in commit b1bfc2d55. Codecov will refresh from the updated branch.