Writes failing tests first, establishing a strict implementation contract for test-driven development.

• Completes the RED phase of TDD by authoring behavior-focused tests that fail for the right reason, then hands off to implementation agents with objective pass criteria
• Delegates test authoring to a tdd_test_writer subagent when available, ensuring tests remain unmodified during implementation
• Detects existing test frameworks and conventions (pytest, jest, vitest, go test, cargo test) and follows repository patterns for consistency
• Produces a structured handoff block specifying exact test files, verification commands, failure summaries, and immutable test constraints that implementation agents must satisfy without weakening tests
• Supports bugfix workflows by adding regression tests that capture the reported failure mode before code changes