Chore: Add warn in fal run if the app startup time exceeds startup timeout.

[mittal-ishaan]

To check for startup timeout in fal run, we wrap a timer around setup function and check how much time is it taking

[linear]

SERV-3 Warn in `fal run` when startup timeout would trigger

[mittal-ishaan]

@claude review

[claude]

Claude finished @mittal-ishaan's task in 1m 34s —— View job

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Code Review

• Read changed files and gather context
• Review app.py changes
• Review test_app.py changes
• Post final review

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Overall the change is clean and well-tested. A few observations below.

projects/fal/src/fal/app.py

1. Use logger.warning instead of print

The module already uses a structured logger (logger = get_logger(__name__) at module level). Using print for this warning is inconsistent with the rest of the codebase. Prefer:

logger.warning(
    "App setup exceeded startup_timeout (%s.1fs > %ss). "
    "`fal deploy` would have triggered the startup timeout.",
    setup_elapsed, effective_startup_timeout,
)

Fix this →

2. or vs is not None for falsy zero

effective_startup_timeout = (
    self.startup_timeout or DEFAULT_PLATFORM_STARTUP_TIMEOUT
)

If someone ever sets startup_timeout = 0, this silently falls back to 600. While 0 is an unlikely value in practice, the semantically correct check is:

effective_startup_timeout = (
    self.startup_timeout if self.startup_timeout is not None
    else DEFAULT_PLATFORM_STARTUP_TIMEOUT
)

3. Verify the 600s constant

DEFAULT_PLATFORM_STARTUP_TIMEOUT = 600 — worth confirming this matches the actual platform default. The wait_for_app helper in the same file uses startup_timeout: int = 60 (line 230), though that appears to be a local health-check timeout rather than the server-side startup timeout, so the values being different is likely intentional. A brief comment explaining the source of 600 would make this clearer for future readers.

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projects/fal/tests/unit/test_app.py

The tests look solid:

• The parametrize matrix covers the key cases: explicit timeout over/under, default timeout over/under, and the exact-equal boundary ((1, 1.0, False)).
• Patching fal.app.time.perf_counter with side_effect=[0.0, elapsed_seconds] correctly simulates the two calls without actually sleeping.
• The TestApp class is defined inside the test function, so the direct assignment TestApp.startup_timeout = startup_timeout doesn't bleed between parametrize iterations.

One minor nit: the printed_lines construction

printed_lines = ["".join(map(str, call.args)) for call in mock_print.call_args_list]

works correctly here because the warning uses an f-string (single positional arg), but a more idiomatic way to join call.args with a space would be " ".join(map(str, call.args)). Not a bug, just a style note.

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Summary: Two actionable items worth addressing before merge — switch print to logger.warning, and consider the is not None guard. The rest is cosmetic.

[Copilot]

Pull request overview

This PR adds a warning mechanism to fal run to inform users when their application's setup time exceeds the configured startup timeout. This helps users catch performance issues early during local development that would later cause failures in production deployments.

Changes:

• Added a constant DEFAULT_PLATFORM_STARTUP_TIMEOUT = 600 seconds (10 minutes) as the default startup timeout when none is specified
• Wrapped the setup() function call in the lifespan() method with timing measurements using time.perf_counter()
• Added logic to check if the measured setup time exceeds the effective startup timeout and print a warning message if it does
• Added comprehensive parametrized test test_lifespan_startup_timeout_warning with five test cases covering different timeout configurations and elapsed times

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
projects/fal/src/fal/app.py	Added startup timeout measurement and warning logic to the lifespan() method, with a new constant for the default platform timeout
projects/fal/tests/unit/test_app.py	Added parametrized test to verify warning behavior across different timeout and elapsed time combinations

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