Add file length CI check (500-line limit)

[Miyamura80]

Summary

• Adds a Python file length check (make file_len_check) that enforces a 500-line maximum, preventing AI-generated code from becoming monolithic
• Configurable via [tool.file_length] in pyproject.toml with an exclude list for justified exceptions (currently onboard.py at 655 lines)
• Integrated into make ci and the linter GitHub Actions workflow
• Includes a Cursor rule (.cursor/rules/file_length.mdc) documenting the rationale and refactoring guidance

Test plan

• make file_len_check passes with onboard.py excluded
• Verified onboard.py (655 lines) would be caught without the exclusion
• CI workflow runs the check successfully

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR introduces a Python file-length enforcement check (make file_len_check) that fails CI when any .py file exceeds 500 lines, with an opt-out exclude list in pyproject.toml. The check is cleanly integrated into both the make ci target and the GitHub Actions linter workflow.

The implementation is well-structured:

• Directory skipping is correct — root-level dirs are filtered via parts[0], nested cache dirs via parts[:-1]
• Exclusion matching uses rel.as_posix() (previously-flagged Windows path bug is already resolved)
• Config loading has sensible defaults if [tool.file_length] is absent
• The script follows the project's coding style (uppercase constants, built-in generic types, from __future__ import annotations)

No issues found. The previously flagged as_posix() and PurePosixPath concerns have both been addressed.

Confidence Score: 5/5

• Safe to merge — the check is additive, non-breaking, and already passes with the existing codebase.
• All previously flagged issues are resolved, the logic is correct across all identified edge cases, and the integration is consistent with the existing CI setup. No outstanding concerns.
• No files require special attention.

Important Files Changed

Filename	Overview
scripts/check_file_length.py	New script that reads config from pyproject.toml, walks repo .py files skipping relevant cache/vendor directories, and reports files exceeding the configured line limit. Previously-flagged cross-platform path issues (as_posix(), Path annotation) are already resolved.
pyproject.toml	Adds [tool.file_length] section with max_lines = 500 and onboard.py excluded; straightforward config addition consistent with the existing vulture exclude list.
.github/workflows/linter_require_ruff.yaml	Appends the file-length check as a new workflow step; consistent with existing step style in the file.
Makefile	Adds file_len_check target and wires it into the ci target; the updated help comment accurately reflects the new dependency.
.cursor/rules/file_length.mdc	Cursor rule documenting the 500-line limit rationale and how to add exclusions; accurate and consistent with the implementation.

_{Reviews (3): Last reviewed commit: "⚙️ remove refactoring guidance from curs..." | Re-trigger Greptile}