Fix: lfx serve asyncio event loop error

[HzaRashid]

lfx serve [flow-json-file-path] ...] throws the following exception:

✗ Failed to start server: asyncio.run() cannot be called from a running event loop
sys:1: RuntimeWarning: coroutine 'Server.serve' was never awaited
RuntimeWarning: Enable tracemalloc to get the object allocation traceback

because the serve_command handler is wrapped in a syncify decorator which creates its own event loop, while uvicorn.run() tries to create another event loop inside of it. This is fixed by starting the server as a coroutine inside the syncify event loop by calling await server.serve() directly

[coderabbitai]

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Walkthrough

The PR refactors the server startup mechanism in the CLI by replacing a direct uvicorn.run() invocation with explicit uvicorn.Server API usage. It constructs a Config object, instantiates a Server, and awaits its serve() method while maintaining configuration parameters and error handling.

Changes

Cohort / File(s)	Summary
Server startup refactoring src/lfx/src/lfx/cli/commands.py	Replaced uvicorn.run() call with explicit Server API: creates uvicorn.Config, instantiates uvicorn.Server(config), and awaits server.serve(). Host, port, and log_level configuration preserved.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

• Verify that all necessary parameters (host, port, log_level) are correctly passed to the Config object
• Confirm error handling remains intact in the new async/await pattern
• Ensure the Server lifecycle (initialization and serve) is properly managed

Pre-merge checks and finishing touches

Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error, 1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Test Coverage For New Implementations	❌ Error	Test file test_serve.py still mocks uvicorn.run() instead of uvicorn.Server API and lacks asyncio fix regression tests.	Update test_serve.py to mock uvicorn.Server and add regression tests verifying the asyncio event loop fix works correctly.
Test Quality And Coverage	⚠️ Warning	PR fixes critical asyncio event loop error in serve_command by refactoring uvicorn initialization but includes zero test coverage for the async functionality change.	Add comprehensive tests: (1) async test with pytest.mark.asyncio for uvicorn.Server initialization, (2) CliRunner test verifying no event loop errors, (3) error scenario tests, (4) validation that original issue is resolved.
Test File Naming And Structure	❓ Inconclusive	PR modifies only implementation file (src/lfx/src/lfx/cli/commands.py) with no test files added or modified according to the provided summary.	Clarify whether test files were added/modified in this PR. If tests exist, verify they follow naming conventions (test_*.py for Python, *.test.ts/tsx for TypeScript) and proper structure.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Fix: lfx serve asyncio event loop error' directly and specifically describes the main change: resolving an asyncio event loop conflict in the lfx serve command.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Excessive Mock Usage Warning	✅ Passed	PR modifies only CLI command handling; no test files altered, so no excessive mock usage to evaluate.

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[github-actions]

Frontend Unit Test Coverage Report

Coverage Summary

Lines	Statements	Branches	Functions
	15.45% (4251/27504)	8.62% (1812/21011)	9.7% (588/6059)

Unit Test Results

Tests	Skipped	Failures	Errors	Time
1671	0 💤	0 ❌	0 🔥	21.309s ⏱️

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 32.54%. Comparing base (21e257a) to head (68daae8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10887      +/-   ##
==========================================
- Coverage   32.54%   32.54%   -0.01%     
==========================================
  Files        1370     1370              
  Lines       63543    63544       +1     
  Branches     9394     9393       -1     
==========================================
  Hits        20680    20680              
  Misses      41824    41824              
- Partials     1039     1040       +1     

Flag	Coverage Δ
backend	51.54% <ø> (-0.03%)	⬇️
frontend	14.30% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
src/lfx/src/lfx/cli/commands.py	52.90% <ø> (-0.31%)	⬇️

... and 7 files with indirect coverage changes

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