feat(#2659): serve hive-matrix-mcp over persistent streamable-http, drop stdio bridge

hive-matrix-mcp/README.md

@@ -0,0 +1,36 @@
+# hive-matrix-mcp
+
+Per-agent matrix integration: a long-running daemon
+(`hive-matrix-daemon`) that holds a matrix-sdk `Client` + sync loop per
+configured account and serves the matrix tool surface (`send_message`,
+`send_dm`, `list_rooms`, `read_room`, …) directly over streamable-http.
+No stdio bridge, no per-turn respawn — claude reconnects to the same
+stable URL every turn.
+
+## When to use it
+
+Look here when changing matrix tool behaviour, multi-account handling,
+or the incoming-event → todo/wake path. The daemon owns the whole
+lifecycle: per-account bring-up (`accounts.rs`, `client.rs`), the sync
+loop that sweeps invites/unread rooms into the harness's in-agent todo
+socket (`timeline.rs`, `wake.rs`), and the MCP tool router itself
+(`mcp.rs`).
+
+## Shape
+
+One bin (`hive-matrix-daemon`, `src/main.rs`) built from the crate's
+own lib (`src/lib.rs`):
+
+- **`accounts.rs`** — multi-account config + the account→`Client`
+  dispatch registry (`main` is always the hive-internal primary; extras
+  come from `HIVE_MATRIX_ACCOUNTS`).
+- **`client.rs`** — session restore, stale-token recovery, avatar sync,
+  cross-signing bootstrap.
+- **`timeline.rs`** / **`wake.rs`** — per-sync-callback invite/unread
+  sweeps that push todos onto `HIVE_AGENT_SOCKET`.
+- **`handlers.rs`** — per-tool dispatch, returns `protocol::DaemonResponse`.
+- **`mcp.rs`** — the `rmcp` tool router + `serve_http`, resolving each
+  call's optional `account` arg against the registry before calling
+  into `handlers`.
+- **`paths.rs`** — per-agent path resolution (token file, matrix-sdk
+  state dir, homeserver URL, accounts snapshot).