Generate unit tests for a .NET service following the coverage-kit conventions. Use when the user asks to 'generate tests', 'backfill tests', 'characterize this service', or 'add tests for' a target after coverage-init has run. Operates in characterization mode (freeze current behavior for existing code) or spec mode (assert intended behavior for new/changed code), enforces the run-capture-fill loop, routes untestable units to the manifest cannot-test log, can fan the backfill out across a user-chosen number of parallel agents for large worklists (asking first, since more agents cost more tokens), and runs a single read-only suite critique before the baseline locks in (auditing cannot-test legitimacy, assertion/C1 depth, systematic gaps, and any frozen defect missing from the manifest latent_bugs backlog, never the C0/C1 numbers themselves).