test(audit): close the four remaining minor items from the May 1 audit

[cmeans-claude-dev]

Summary

Closes the four minor audit items left after PRs #101 and #102. All four are nice-to-haves; none are bugs. Bundled into a single PR per the audit synthesis.

Added

1. clipboard.reset_backend_cache() public helper. Replaces direct mutation of the module-private _backend global in test fixtures (tests/test_server.py and tests/test_integration_x11.py). Production code has no reason to call this; the helper exists for tests that switch backends or re-read MCP_CLIPBOARD_BACKEND mid-process.
2. Direct _has_header_row tests covering the len(rows) < 2 early-return path, the uniform-text-no-header path, and a positive text-header-over-numeric-data case. Previously exercised only indirectly via format_table JSON output.
3. Padding-loop regression test for clipboard_paste(include_schema=True) when the data rows are wider than the header row. Asserts synthetic Col 3 / Col 4 labels are emitted by the padding loop at server.py:222-228.
4. Env-var validation tests for MCP_CLIPBOARD_MAX_WRITE_BYTES and MCP_CLIPBOARD_MAX_IMAGE_BYTES. Both vars are parsed via int(os.environ.get(...)) at module import; non-integer values raise ValueError before anything else runs. Tests exercise each in a subprocess so the partial-import state stays isolated from the in-process module cache.

Implementation note

The env-var-validation tests originally tried importlib.reload() in-process, which broke 21 other tests because their pytest.raises(ClipboardError) calls compared against the pre-reload class object, while the reloaded module raised the new class. Switched to subprocess-based assertions that capture stderr and verify both the ValueError traceback and the offending value appear.

Test plan

• uv run pytest (511 passed, 11 deselected, 5 xfailed)
• uv run ruff check src/ tests/
• uv run ruff format --check src/ tests/
• uv run mypy src/

CHANGELOG

• ## [Unreleased] updated with four ### Added entries referencing test(audit): close the four remaining minor items from the May 1 audit #104.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[cmeans]

[QA] Starting review at 2411086. Will verify the new reset_backend_cache() API, the env-var-validation subprocess tests, the padding-loop regression assertion, and the direct _has_header_row coverage.

[cmeans]

QA review — round 1

Clean cleanup PR at 2411086. Zero findings.

The new reset_backend_cache() helper is the right shape: small, well-documented as test-only, and the migration of the two existing autouse fixtures (tests/test_server.py:1112-1124 and tests/test_integration_x11.py:46-52) is uniform. The subprocess approach for env-var validation tests is the correct call — the PR body's implementation note about importlib.reload() clobbering 21 other tests via class-identity divergence is an accurate diagnosis (a reloaded module's ClipboardError is a different class object than the one captured in already-imported test references). The _has_header_row direct tests cover the len(rows) < 2 early return + the type-comparison branch, and the padding-loop regression test exploits a real ragged-row scenario (HTML parser doesn't normalize widths at parse time, so a 2-cell <th> header followed by 4-cell <td> rows lands ragged in rows, and infer_column_types returns 4 entries based on max_cols — headers then needs synthetic Col 3 / Col 4 labels). All four CHANGELOG entries reference #104 and KaC ordering is preserved.

Verification

Check	Status
uv run pytest	511 passed, 11 deselected, 5 xfailed — matches PR body claim (504 prior + 7 new = 4 _has_header_row + 2 env-var subprocess + 1 padding-loop)
uv run ruff check src/ tests/	clean
uv run ruff format --check src/ tests/	10 files already formatted
uv run mypy src/	clean
Repo-wide grep for residual cb._backend = / clipboard._backend = direct mutation	0 hits in tests/ and src/ — both fixtures fully migrated to reset_backend_cache()
Manual import of reset_backend_cache	imports cleanly, docstring renders correctly
Manual reproduction of env-var ValueError	MCP_CLIPBOARD_MAX_IMAGE_BYTES=ten-megs uv run python -c "import mcp_clipboard.clipboard" raises ValueError: invalid literal for int() with base 10: 'ten-megs' at line 41 of clipboard.py — confirms the subprocess test's assertions are exercising real behavior
_has_header_row test coverage	all four added tests target a distinct branch: len(rows) < 2 early return (single + empty), uniform-text negative case, text-over-numeric positive case
CI gates	all green (lint, typecheck, test 3.11/3.12/3.13, integration-x11, codecov/patch, qa-approved)

PR-body checkboxes all flipped.

Applying Ready for QA Signoff as the final act. Awaiting maintainer QA Approved.

[cmeans]

[QA] Verdict: Ready for QA Signoff. Single round, zero findings. Gates re-verified (511/11/5, ruff/format/mypy clean, CI green); reset_backend_cache migration complete (zero residual direct _backend mutations); env-var ValueError reproduces manually. Awaiting maintainer QA Approved.

[cmeans]

LGTM