- matrix.py: Transport implementation over the Matrix client-server HTTP API directly (token auth, /sync long-poll, /send) using the existing httpx dependency — no Matrix SDK; four endpoints total. Deviation from the presented plan (matrix-nio) flagged in the PR - First sync learns position and skips backlog, so room history is never delivered as context (A1); own messages and non-message events filtered; sender MXID passed through for the orchestrator's operator allowlist - Sync loop backs off (capped at 60s) and retries indefinitely on homeserver errors, mirroring B2's polling posture - Encrypted rooms unsupported: bot rooms are created unencrypted until E2E lands (operator decision; room recreated accordingly) - NISSE_MATRIX_TEST_ROOM_ID added: the live smoke test binds only to the dedicated test room, never the production room - 8 unit tests over a mocked HTTP layer; live integration test verified against the real homeserver Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>