Purpose
-------
Validate the linter's header auto-fixing logic.
Responsibilities
----------------
- Ensure missing or incorrect header lines are corrected.
- Ensure duplicates and misplaced lines are removed.
- Ensure docstrings and code remain intact.
- Ensure backup files are created.
Diagnostics
-----------
Domain: LINTER-TESTS
Levels:
L2 — lifecycle
L3 — semantic details
L4 — deep tracing
Contracts
---------
- Must not modify fixtures outside the temporary project root.
- Must verify correctness of the rewritten header block.
- Must ensure no corruption of module content.