core: add AST-based linter for undeclared state reads in function-bas…

[Smitaambiger]

Closes #407

This PR adds AST-based validation for undeclared state reads in function-based actions.

What this does

• Parses the originating function using inspect.getsource
• Walks the AST to detect state["<literal>"] accesses
• Compares detected keys with declared reads=[...]
• Raises ValueError if undeclared keys are accessed
• Skips validation when source is unavailable

Why

Prevents silent bugs caused by accessing state keys that were not declared in reads, enforcing stricter action correctness.

Tests

• Added unit tests covering:
  • Valid declared reads
  • Undeclared read detection

[Smitaambiger]

@elijahbenizzy

Initial implementation for AST-based undeclared state read validation.

Currently implemented as a hard ValueError at action construction time.

Happy to adjust:

• validation timing (build-time vs decorator-time)
• severity (warning vs error)

Looking forward to feedback.

[skrawcz]

good start, a few things to add.

[Smitaambiger]

@skrawcz ,Thanks for the detailed feedback!

Addressed the requested changes:

• Moved imports to top level
• Consolidated tests into test_action.py
• Added test for multiple undeclared keys interleaved with declared keys
• Added regression test to ensure pydantic-based actions are not impacted
• Cleaned up lint/formatting issues

Core tests are passing locally and CI should reflect the same.

(.venv) PS C:\Users\gouta\OneDrive\Desktop\burr> python -m pytest tests/core -q
................................................................................................................................................................................................. [ 69%]
....................................................................................                                                                                                              [100%]
277 passed in 9.10s

(.venv) PS C:\Users\gouta\OneDrive\Desktop\burr> pre-commit run --all-files
black....................................................................Passed
trim trailing whitespace.................................................Passed
fix end of files.........................................................Passed
fix requirements.txt.....................................................Passed
check python ast.........................................................Passed
isort....................................................................Passed
flake8...................................................................Passed
frontend-lint-staged.....................................................Passed

Please let me know if any further adjustments are needed.

[Smitaambiger]

@skrawcz Just following up — please let me know if anything else needs adjustment here. Happy to iterate further if needed.

[skrawcz]

Great thanks!

[Smitaambiger]

@skrawcz Thanks for the review and guidance — really enjoyed working on this one!