fix: graceful HTTP server shutdown with in-flight request draining

[enriquevalenzuelagalaxy]

PR Description

Adds graceful HTTP server shutdown to Runner. When close() is called, the server now waits for any in-flight HTTP requests to complete before closing the Vert.x HttpServer, preventing abrupt connection resets under load or during rolling restarts.

Changes:

• Added trackInFlightRequests() — wraps the request handler to atomically increment/decrement an in-flight counter, guarded against double-counting via AtomicBoolean per request
• Added waitForInFlightRequestsToComplete() — blocks the shutdown thread (up to 20 seconds) using Object.wait/notifyAll on a monitor
• Added gracefulHttpShutdown() — drains in-flight requests then closes the HttpServer via its async close() with a latch
• Modified close() to call gracefulHttpShutdown() before closing other resources
• httpServer promoted from local variable to volatile instance field so close() can reference it

Fixed Issue(s)

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.

Testing

• I thought about testing these changes in a realistic/non-local environment.

RunnerGracefulShutdownTest covers three scenarios using a real embedded Vert.x server:

1. closeWaitsForInFlightRequestBeforeShuttingDown — verifies close() blocks until a slow in-flight request completes before returning
2. closeCompletesNormallyWithNoInFlightRequests — verifies close() doesn't block when idle
3. closeBeforeRunDoesNotThrow — verifies the null-guard on httpServer is correct

---

Note

Medium Risk
Changes core HTTP lifecycle and shutdown ordering for a signing service; bounded timeouts mean very long requests may still be cut off, but signing logic is unchanged.

Overview
Runner.close() now drains active HTTP work before tearing down other resources, so rolling restarts and shutdown under load are less likely to reset connections mid-signing.

Shutdown sets a shuttingDown flag and wraps the Vert.x request handler with trackInFlightRequests, which counts in-flight requests, rejects new ones with 503 once shutdown has started, and decrements on response completion (with guards against double-counting). gracefulHttpShutdown waits up to 20 seconds for the counter to reach zero, then closes the HttpServer asynchronously with a bounded wait. The server instance is stored on the runner so close() can run this path even when run() was never started (null-safe).

RunnerGracefulShutdownTest exercises blocking close() until a slow handler finishes, idle shutdown, and close() before run().

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[github-actions]

All contributors have signed the CLA ✍️ ✅
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[enriquevalenzuelagalaxy]

I have read the CLA Document and I hereby sign the CLA

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Reviewed by Cursor Bugbot for commit 3e7d4a2. Configure here.}

[ejether]

I have read the CLA Document and I hereby sign the CLA

[sonarqubecloud]

Quality Gate passed

Issues
9 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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