#22056 pre-commit registers only the commit's own tests

The pre-commit hook registers only the commit's own tests: the ones it adds, and the ones its workflow changes name. Part of #21946.

Before, the hook ran the registry writer over every unregistered test in the repository. If the base had a straggler, whichever pull request committed a test next carried it too. Every PR then added the same registry entries, and they conflicted with each other. The click-through lane hit this on #21272 with tests/test_cmux_next_base_autofix_finishes.py and tests/test_nightly_next_feed_rollback.py. This PR registers those two once on the base.

Change

• validate_test_execution_registry.py --write takes a repeatable --only PATH, and register_derivable(root, only=...) registers just those paths. With no --only, it registers everything, as before.
• The hook collects the tests it passes from git diff --cached:
  • test files the commit adds;
  • tests/test_*.py paths on added lines in workflow files.

Tests (committed failing first)

• tests/test_install_git_hooks.py, test_pre_commit_registers_only_the_commits_own_tests. A repository whose base has an unregistered test_base.py commits test_mine.py.
  • Red: the hook registered both.
  • Green: it registers only test_mine.py.
• tests/test_ci_test_execution_registry.py, test_write_only_registers_the_named_tests.
  • Red: TypeError, since only didn't exist.
  • Green at the head.
• All of test_install_git_hooks passes.
• LaneRunnerTests.test_verify_local_jobs_option_keeps_recipe_tests_live fails both before and after this change in this sparse checkout.
• The registry validator's "not run by any workflow" errors appear identically with the base registry, so they also predate this change.

The installed hook copies refresh when scripts/install-git-hooks.sh reruns, which post-merge does. A clone that still has the old validator copy ignores --only with an error, and the hook continues because registration is best effort.

Changelog

none

🤖 Generated with Claude Code

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Summary by cubic

Stops the pre-commit hook from writing the base's unregistered tests into every pull request. Part of #21946.

Before, the hook ran the registry writer over every unregistered test in the repository, so a stray test on the base got carried into whichever PR committed a test next, and identical registry entries conflicted across PRs. Now the hook registers only the tests the commit adds or that its workflow changes name. The base's two stragglers (tests/test_cmux_next_base_autofix_finishes.py, tests/test_nightly_next_feed_rollback.py) are registered once here.

Changes

• validate_test_execution_registry.py --write accepts a repeatable --only PATH; without it, behavior is unchanged.
• The hook collects candidates from git diff --cached: added tests/test_*.py files and test paths on added lines in workflow files.