🐛 Skip keep-warm import of handler.keep_warm_callback (#1469)

[dennybiasiolli]

Summary

Fixes #1469.

When keep_warm is on (the default), Zappa schedules an EventBridge rule whose target is hardcoded as handler.keep_warm_callback. On invoke, LambdaHandler treats that string as an import path. That works for a classic zip (the package copies zappa/handler.py to the archive root as handler.py). It fails for a custom lambda_handler / container image that has no top-level handler module:

ModuleNotFoundError: No module named 'handler'

HTTP can still succeed. The keep-warm ping fails every few minutes.

Fix

In the Scheduled Event branch, if the extracted function name ends in keep_warm_callback, return after LambdaHandler construction. Do not import handler.keep_warm_callback.

• Existing EventBridge rules keep their current name, so this fixes production on the next code deploy.
• Classic zip deploys are unchanged.
• User-configured scheduled functions still import and run (function cannot contain hyphens, so split("-")[-1] is the full dotted path).
• The extra keep_warm_callback re-entry (lambda_handler(event={})) was not load-bearing: __init__ already loads the app.

The CLI still schedules handler.keep_warm_callback. Changing that string would rename the rule and would not fix existing rules.

Test plan

• test_keep_warm_scheduled_event_without_handler_module — Scheduled Event whose rule ARN ends in zappa-keep-warm-handler.keep_warm_callback, with no top-level handler module, must not raise ModuleNotFoundError. Fails without the special-case, passes with it.
• test_scheduled_event_invokes_target_function — a real scheduled target (tests.test_app.schedule_me) still imports and runs.
• All 28 tests/test_handler.py tests pass; black, isort, flake8 clean on touched Python.

Fixes #1469

[coveralls]

coverage: 74.816% (+0.03%) from 74.785% — dennybiasiolli:fix/1469-keep-warm-handler-import into zappa:master