fix: AE-2316: field validator for serverless idleTimeout

[jhcipar]

adds a field validator to idleTimeout so errors happen at construction time rather than deploy time; backend currently restricts idleTimeout to between 1 and 3600s.

[promptless]

📝 Documentation updates detected!

New suggestion: Document valid range for idle_timeout parameter

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[Copilot]

Pull request overview

This PR adds construction-time validation for the idleTimeout field on serverless endpoints to match backend constraints (1–3600 seconds), preventing invalid configs from failing later at deploy time.

Changes:

• Add a Pydantic field_validator for idleTimeout in ServerlessResource.
• Add unit tests covering invalid and boundary-valid idleTimeout values for ServerlessResource.
• Add a unit test confirming LiveServerless rejects an invalid idleTimeout.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/runpod_flash/core/resources/serverless.py	Enforces idleTimeout range (1–3600) during model construction via field_validator.
tests/unit/resources/test_serverless.py	Adds parametrized tests for invalid values and valid boundary values.
tests/unit/resources/test_live_serverless.py	Adds a regression test ensuring LiveServerless inherits/enforces the idleTimeout validation.

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[runpod-Henrik]

1. Validator correctness and placement
   The validator is placed on ServerlessResource, which is the common base for all concrete resource types. A single validator here covers the entire hierarchy. The bounds 1 <= value <= 3600 match the stated backend restriction. The default of 60 falls within the valid range. The None pass-through is correct.

2. Error timing for Endpoint users
   The PR description says "errors happen at construction time rather than deploy time." This is true for direct ServerlessResource use. For Endpoint users (@endpoint(idle_timeout=...)), the error fires at decoration time — still much better than deploy time, and acceptable behavior.

3. Test coverage
   test_serverless.py has good parametric coverage: [0, -1, 3601] for rejection and [1, 3600] for boundary acceptance.

test_live_serverless.py adds only a single test (idleTimeout=0). Missing: upper bound rejection (3601) and valid boundary acceptance (1, 3600). Since LiveServerless inherits the validator with no override, the gap is low risk, but inconsistent with the base-class test pattern established in this same PR.

4. Missing Endpoint-level unit test
   The new unit tests exercise ServerlessResource and LiveServerless directly. There is no unit-level test for Endpoint(idle_timeout=0) or Endpoint(idle_timeout=3601) raising ValueError. A companion test in test_endpoint.py would complete the coverage.

Nits
Error message says "idleTimeout must be between 1 and 3600 seconds" — camelCase matches other validators in the file. Consistent.
Verdict
PASS WITH NITS — validator is correct, placement covers the full class hierarchy, and bounds match the stated backend constraint. The test_live_serverless.py addition only tests one of the three rejection cases covered in test_serverless.py; rounding it out would be a small improvement.

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