fix(api): return 400 for non-positive per_page instead of 500

[Syed-Ali-Abbas-Zaidi]

The work items list endpoint (and every other paginated v1 endpoint) validated per_page for non-numeric and oversized values but not for zero or negative ones. Those fell through get_per_page and crashed downstream in the paginator, surfacing as an unhelpful HTTP 500 that clients retry.

Reject per_page <= 0 in BasePaginator.get_per_page with a 400 ParseError ("Invalid per_page value. Must be a positive integer."), matching the existing non-numeric and too-large validation cases.

Add contract tests covering per_page=0, negative, non-numeric, oversized, and valid values on the work items list endpoint.

Closes #9426

Description

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Improvement (change that would cause existing functionality to not work as expected)
• Code refactoring
• Performance improvements
• Documentation update

Screenshots and Media (if applicable)

Test Scenarios

References

Summary by CodeRabbit

• Bug Fixes
  • Improved validation for issue list pagination.
  • Invalid, non-numeric, non-positive, or excessively large per_page values now return a clear HTTP 400 error.
  • Valid pagination values continue to work as expected.

[CLAassistant]

All committers have signed the CLA.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ef9d408c-69f1-4338-aa01-1c1e02821398

📥 Commits

Reviewing files that changed from the base of the PR and between af1be50 and 0f27fe2.

📒 Files selected for processing (2)

• apps/api/plane/tests/contract/api/test_issues.py
• apps/api/plane/utils/paginator.py

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📝 Walkthrough

Walkthrough

The paginator now rejects non-positive per_page values with a validation error. Contract tests cover zero, negative, non-numeric, oversized, and valid per_page values for the issues list endpoint.

Changes

per_page validation

Layer / File(s)	Summary
Paginator validation and issue-list coverage apps/api/plane/utils/paginator.py, apps/api/plane/tests/contract/api/test_issues.py	BasePaginator rejects non-positive values with a ParseError, and contract tests verify 400 responses for invalid values and 200 for a valid value.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: dheeru0198

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main fix: returning 400 for non-positive per_page values instead of 500.
Description check	✅ Passed	The description covers the change, type of change, issue reference, and test coverage, matching the template well.
Linked Issues check	✅ Passed	The code updates BasePaginator validation and adds tests for zero, negative, non-numeric, oversized, and valid per_page cases, matching #9426.
Out of Scope Changes check	✅ Passed	The changes are limited to paginator validation and related contract tests, with no clear out-of-scope additions.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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