feat(fleet): F4 Phase 2a — Matrix CS-API connector client + factory (#618)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

docs/scratchpads/f4-matrix-connector.md

@@ -17,3 +17,14 @@
 ## Phase 2+ (follow-ups, in the doc)
 
 Matrix CS-API client (fetch send/sync/health) + factory; init/configure connector-selection UX + roster-parse wiring; systemd launch wiring; Conduit deploy guide; first-party Mosaic Discord (threads) as a connector.
+
+## Phase 2a (feat/f4-matrix-client, stacked on #617) — Matrix CS-API client
+
+- `src/fleet/connectors/matrix.ts`: `MatrixConnector implements OrchestratorConnector` over the Matrix
+  client-server API (injectable fetch, no SDK). `send` → PUT m.room.message (thread-aware); `subscribe`
+  → /sync long-poll loop using the pure `parseSyncResponse`; `health` → /versions + /whoami.
+  `registerMatrixConnector(env)` registers the factory (token from MATRIX_ACCESS_TOKEN, never roster).
+- Pure helpers `buildMessageBody` + `parseSyncResponse` make send/receive unit-testable.
+- 13 Matrix tests + 7 registry = 20 connector tests green; tsc/eslint/prettier clean.
+- Remaining Phase 2: init/configure connector-selection UX + roster-parse wiring (touches fleet.ts —
+  after #615); systemd launch wiring; Conduit deploy guide.