fix(api): non-blocking asyncio.sleep in lifespan db-retry backoff (#140)

[Jovonni]

What

The FastAPI startup lifespan retried init_db() with a blocking time.sleep(retry_delay) inside an async def. That blocks the event loop for the full backoff window on every failed attempt, so anything sharing the loop from the first instant (health/readiness probes) can be delayed while the DB is reconnecting.

Swaps it for await asyncio.sleep(retry_delay) (non-blocking), and adds import asyncio at module top.

Why

Flagged in #140 — small, correct one-liner with a real (if narrow) impact on startup responsiveness.

Tests

New regression subsuite core/tests/test_lifespan_async.py:

• static guard — the lifespan source contains no time.sleep and uses await asyncio.sleep
• functional — init_db() fails once then succeeds; asserts the retry path awaits the non-blocking sleep exactly once (event loop never blocks)

Runs under the existing core/tests/ pytest suite in CI.

Closes #140

[Copilot]

Pull request overview

This PR improves FastAPI startup responsiveness by replacing a blocking backoff (time.sleep) inside the async lifespan retry loop with a non-blocking await asyncio.sleep, and adds a regression test to prevent reintroducing blocking sleeps in the future.

Changes:

• Replace time.sleep(retry_delay) with await asyncio.sleep(retry_delay) in the lifespan DB-init retry backoff.
• Add import asyncio to support the non-blocking sleep call.
• Add a new pytest module covering both a static guard and a functional retry/backoff behavior check.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
core/fastapi_app.py	Switches lifespan retry backoff to non-blocking await asyncio.sleep and imports asyncio.
core/tests/test_lifespan_async.py	Adds regression tests asserting the lifespan retry path uses non-blocking sleep.

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