gate: a branch taken per operating system needs a test that injects one

[EdbertChan]

Summary

This check helps maintainers trust that hook checks cover the paths their tools may take.

Checks passed on one computer but failed in Linux automation.

The check did not require a chosen operating system.

It now requires each check to supply that choice, so both paths are exercised.

Review Claim

Require operating-system branches to be tested with an explicit operating-system choice.

Review Lane

behavior

Review Unit

engine-runtime

Safety Invariant

Only test-coverage detection changes; runtime hooks and detectors keep their existing behavior.

Slice Rationale

This slice adds the missing coverage rule and its focused tests. It stays separate from runtime hook changes because none are included.

Non-goals

• Do not change runtime hooks or detector behavior.
• Do not change existing positive and negative coverage rules.
• Do not change the operating system used by automation.

Test Plan

Test Plan

• python3 -m unittest tests/test_check_hook_test_coverage.py

  ........
  ----------------------------------------------------------------------
  Ran 8 tests in 0.132s
  
  OK
  

• Full repository test suite was not run.

The focused tests cover a missing platform injection, a supplied platform injection, and a detector without an operating-system branch. Backtested against the tests as first written: fires. Against the fixed ones: silent.

Depends-On: #508

Revert Plan

Revert Plan

• Safe to revert? Yes.
• Revert command: git revert <sha> or equivalent.
• Post-revert steps: Re-run the focused test command and the PR body checker.
• Data migration? No.

Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01KU2pPKob4MJ1NqjsfTNyYJ

[EdbertChan]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	hook: a script handed to the user is a claim that it runs	#506
2	audit(token_audit): count "bogus" and "it didn't run" as the same class	#507
3	hook: refuse a quoted command string passed through a login shell	#508
4	gate: a branch taken per operating system needs a test that injects one	#509	👈
5	audit(token_audit): one submission carrying two slash commands is one message	#510
6	audit: use the transcript's own markers for what the human actually sent	#511
7	README: list the handoff-needs-smoke-test and remote-payload-collapses hooks	#535

[cursor]

Bugbot couldn't run - usage limit reached

Bugbot is counted against Cursor usage for this user or team, and this run hit a usage or spend limit.

A user or team admin can review and increase usage limits in the Cursor dashboard.

(requestId: serverGenReqId_5ede4904-9e80-419f-8b01-70487cd603c6)

[cursor]

Bugbot couldn't run - usage limit reached

Bugbot is counted against Cursor usage for this user or team, and this run hit a usage or spend limit.

A user or team admin can review and increase usage limits in the Cursor dashboard.

(requestId: serverGenReqId_80a80e17-fd28-4b60-9c0a-d5be721a00fc)

[EdbertChan]

Revision history

#	Type	Changes	Reason	Date
1	initial	1ec58f5		2026-09-13 05:55 UTC
2	rebase	1ec58f5 → c17c8d3 (rebase only)		2026-09-13 05:55 UTC