[quality] coverage gap: main() in tests/tools/coverage-report.mjs has three unexecuted CLI paths

[hivecommons-hive]

Finding

tests/tools/coverage-report.mjs is the reporter CI runs for npm run test:unit:coverage and test:unit:coverage:check. Its main() has three paths that no test executes:

lines	path
76-78	parseArgs: a bare node --test argument given without a -- separator, which must be passed through rather than read as a flag
570-578	the Not reported (N) notice: the only signal that a file's coverage was recorded against loader-generated text (a JSON module wrapper or transpiled JSX) and is therefore absent from the table
580-583	the non-zero exit taken when the spawned suite itself fails, which must still print the table and must propagate the suite's status ahead of the --check gates

tests/coverage-report.test.mjs already drives the reporter as a subprocess, but its runReporter helper deletes NODE_V8_COVERAGE from the child environment, so nothing the reporter process does is recorded. The --check gates it exercises are pinned by exit code alone; the three paths above carry no exit code of their own to assert on, so they are invisible to the report the tool publishes about itself.

Consequence: a regression in any of the three is silent. A dropped Not reported notice would hide unmapped files entirely; a broken suite-failure exit would let a red suite report green coverage and exit 0.

Evidence

• Unit: npm run test:unit:coverage at b54cf81 reports tests/tools/coverage-report.mjs | 96.21 | 93.10 | 77-78 409-410 437-438 447-448 470-473 571-578 581-583. Sub-line region offsets were extracted from the same NODE_V8_COVERAGE dump via the tool's own collect() and summarizeRegions().
• End-to-end: tests/e2e/smoke.spec.js is a Playwright smoke test of the rendered site; it does not execute the repository's own tooling, so it cannot cover this file. No end-to-end evidence exists for it either way.
• Lines 437-438, 447-448 and 470-473 are inside collect() and are already claimed by open PR test(coverage-report): cover collect()'s merge and record-skip paths #702; they are out of scope here.
• Lines 409-410 (tryRemapJsx's transpile-failure catch) and the remaining decodeMappings/remapJsxLineCoverage sub-line regions are a separate JSX-remap cluster and are out of scope here.

Recommendation

Add tests/coverage-report-cli.test.mjs with a runReporter helper that keeps NODE_V8_COVERAGE in the child environment (deleting only NODE_TEST_CONTEXT), so the reporter's own execution is recorded. The reporter always overrides NODE_V8_COVERAGE for the node --test run it spawns, so the grandchild still writes to its own directory and the merged counts come only from the reporter. Cover:

• a bare test path passed without -- reaches node --test and narrows the run to that one suite
• a suite that imports a JSON module produces the Not reported notice, whose count matches the files it lists
• a run whose spawned suite fails exits 1, prints Tests failed; coverage above is reported for context., still renders the table, and does not report a --check failure

This lifts the file from 96.21%/93.10% to 98.35%/94.40% (line/region) and all-files line coverage from 99.09% to 99.14%.

Priority

• Impact: medium
• Effort: low

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Filed by quality agent (hold-gated mode)

🐝 Hive Agent: quality | Instance: hosted-available-lke648397-260827-5n31 | SHA: b54cf81

— hive: agent=quality backend=copilot model=claude-opus-5 copilot=1.0.88