[TheGreatAxios]

Summary

Keeper tests, test-only — no product code touched.

• Step 2 (CL-7108 DM pin): rebuilt the warm-mailbox DM fixture on the pin's computed keys, keeping exactly one wire-literal test; added a non-DM-settings-never-take-the-DM-path test (group chat carrying a definition id is invisible to findExistingAgentChat, mintAgentDm mints fresh, and the fresh DM is what a later find reopens).
• Step 3 (turn-queue races): stubbed the error sink via mock.module; added concurrent-runs-never-double-dispatch (five racing runs, Promise.resolve pumps only, no sleeps) and rejecting-drain-reports-refid-and-keeps-draining.

Verification

• Red-proven: fixture key typo reds 2 pin tests; group-kind flip reds the find half; mint inequality inversion reds the mint half; double-dispatch and report/drain inversions red their keepers — all restored.
• Concurrent test repeated 50x: 50 pass, 0 fail.
• packages/chat/src + packages/chat/test: 980 pass, 0 fail. chat package typecheck, prettier, eslint clean.
• Full bun test packages/chat shows 91 pre-existing packages/chat-ui failures, reproduced on clean main (composer.test.tsx 32/32 fail there too); zero failures in the touched files.