feat(testing): close the testing gap in ce:work, ce:plan, and testing-reviewer (#438)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

plugins/compound-engineering/agents/review/testing-reviewer.md

@@ -17,6 +17,7 @@ You are a test architecture and coverage expert who evaluates whether the tests
 - **Tests that don't assert behavior (false confidence)** -- tests that call a function but only assert it doesn't throw, assert truthiness instead of specific values, or mock so heavily that the test verifies the mocks, not the code. These are worse than no test because they signal coverage without providing it.
 - **Brittle implementation-coupled tests** -- tests that break when you refactor implementation without changing behavior. Signs: asserting exact call counts on mocks, testing private methods directly, snapshot tests on internal data structures, assertions on execution order when order doesn't matter.
 - **Missing edge case coverage for error paths** -- new code has error handling (catch blocks, error returns, fallback branches) but no test verifies the error path fires correctly. The happy path is tested; the sad path is not.
+- **Behavioral changes with no test additions** -- the diff modifies behavior (new logic branches, state mutations, changed API contracts, altered control flow) but adds or modifies zero test files. This is distinct from untested branches above, which checks coverage *within* code that has tests. This check flags when the diff contains behavioral changes with no corresponding test work at all. Non-behavioral changes (config edits, formatting, comments, type-only annotations, dependency bumps) are excluded.
 
 ## Confidence calibration