Fix: Kill the server with one keyboard interrupt

[Copilot]

Summary

Pressing Ctrl+C once printed a uvicorn traceback and required a second Ctrl+C to fully exit. There were two separate causes:

1. Traceback on first Ctrl+C: uvicorn's capture_signals() re-raises the captured signal via signal.raise_signal() after graceful shutdown, causing an unhandled KeyboardInterrupt to bubble up through loop.run_until_complete(server.serve()).

2. Process hanging after first Ctrl+C: Even after catching the KeyboardInterrupt, the process would hang indefinitely because Python's interpreter tried to join non-daemon background threads (e.g. the model install service thread) during shutdown.

Fix: wrap the serve call in run_app.py with a try/except KeyboardInterrupt that logs a clean shutdown message and then calls os._exit(0) to force an immediate process exit, bypassing Python's thread-joining phase:

try:
    loop.run_until_complete(server.serve())
except KeyboardInterrupt:
    logger.info("InvokeAI shutting down...")
    # Force exit to avoid hanging on non-daemon background threads (e.g. model install service).
    os._exit(0)

Uvicorn's graceful shutdown still runs normally before the KeyboardInterrupt is re-raised. Normal server exits (e.g. via API shutdown endpoint) are unaffected.

Related Issues / Discussions

QA Instructions

Start invokeai-web and press Ctrl+C once. The server should exit immediately and cleanly with an InvokeAI shutting down... log line, no traceback, and no need to press Ctrl+C a second time.

Merge Plan

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[enhancement]: Kill the server with one keyboard interrupt</issue_title>
<issue_description>### Is there an existing issue for this?

• I have searched the existing issues

Contact Details

No response

What should this feature add?

Currently to kill invokeai-web from the command line, you must press ^C twice. The first ^C gives this:

^C[2026-02-26 18:56:13,606]::[ModelInstallService]::INFO --> Installer thread 139253501650624 exiting                                                                                                         
Traceback (most recent call last):                                                                      
  File "/home/lstein/invokeai-lstein/.venv/bin/invokeai-web", line 12, in <module>                                                                                                                              
    sys.exit(run_app())                                                                                 
             ^^^^^^^^^                                                                                  
  File "/home/lstein/Projects/InvokeAI-lstein/invokeai/app/run_app.py", line 103, in run_app                                                                                                                    
    loop.run_until_complete(server.serve())                                                                                                                                                                     
  File "/home/lstein/.local/share/uv/python/cpython-3.12.12-linux-x86_64-gnu/lib/python3.12/asyncio/base_events.py", line 678, in run_until_complete                                                            
    self.run_forever()                                                                                                                                                                                          
  File "/home/lstein/.local/share/uv/python/cpython-3.12.12-linux-x86_64-gnu/lib/python3.12/asyncio/base_events.py", line 645, in run_forever                                                                   
    self._run_once()                                                                                                                                                                                            
  File "/home/lstein/.local/share/uv/python/cpython-3.12.12-linux-x86_64-gnu/lib/python3.12/asyncio/base_events.py", line 1999, in _run_once                                                                    
    handle._run()                                                                                                                                                                                               
  File "/home/lstein/.local/share/uv/python/cpython-3.12.12-linux-x86_64-gnu/lib/python3.12/asyncio/events.py", line 88, in _run                                                                                
    self._context.run(self._callback, *self._args)                                                                                                                                                              
  File "/home/lstein/invokeai-lstein/.venv/lib/python3.12/site-packages/uvicorn/server.py", line 70, in serve                                                                                                   
    with self.capture_signals():                                                                                                                                                                                
         ^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                                                 
  File "/home/lstein/.local/share/uv/python/cpython-3.12.12-linux-x86_64-gnu/lib/python3.12/contextlib.py", line 144, in __exit__                                                                               
    next(self.gen)                                                                                                                                                                                              
  File "/home/lstein/invokeai-lstein/.venv/lib/python3.12/site-packages/uvicorn/server.py", line 331, in capture_signals                                                                                        
    signal.raise_signal(captured_signal)   
KeyboardInterrupt                                                                                                                                                                      

The second ^C gives these messages and it does finally shut down:

</details>



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- Fixes lstein/InvokeAI#93

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[lstein]

Almost, but not quite. After running for a while I still have to press ^C twice. Here's the first time:

^C[2026-02-26 19:17:48,392]::[ModelInstallService]::INFO --> Installer thread 140553368897216 exiting
[2026-02-26 19:17:49,395]::[InvokeAI]::INFO --> InvokeAI shutting down...

I waited for about 30s and then ^C again:

^CException ignored in: <module 'threading' from '/home/lstein/.local/share/uv/python/cpython-3.12.12-linux-x86_64-gnu/lib/python3.12/threading.py'>
Traceback (most recent call last):
  File "/home/lstein/.local/share/uv/python/cpython-3.12.12-linux-x86_64-gnu/lib/python3.12/threading.py", line 1624, in _shutdown
    lock.acquire()
KeyboardInterrupt: 

[Copilot]

Almost, but not quite. After running for a while I still have to press ^C twice. Here's the first time:

^C[2026-02-26 19:17:48,392]::[ModelInstallService]::INFO --> Installer thread 14055336889721...

The root cause was that after catching KeyboardInterrupt, the process still hung waiting for non-daemon background threads (model install service, etc.) to finish — hence the second Ctrl+C.

Fixed in commit 1f0f476 by calling os._exit(0) immediately after logging the shutdown message. This forces an immediate process exit, bypassing Python's thread-joining phase entirely. It's scoped only to the KeyboardInterrupt path, so a normal server stop still returns cleanly.

[lstein]

Works as advertised.