agent socket: external wake-up path for in-container MCP servers

new AgentRequest::Wake { from, body } drops a message into
this agent's inbox via the per-agent socket. matrix-style MCP
servers can use it when they receive an external event
(matrix message, webhook, scrape result) to nudge claude
into running a turn. broker.send wakes whatever Recv is
currently long-polling, the harness picks the message up,
formats a wake prompt with the caller's chosen from label
('matrix: new dm', 'webhook: deploy succeeded', etc.).

new `hive-ag3nt wake --from <label> --body <text>` subcommand
on the harness binary so MCP servers can shell out instead of
implementing the line-JSON protocol themselves; body=='-'
reads from stdin for multi-line / quoting-friendly payloads.

identity = socket: anything that can connect to /run/hive/mcp
.sock is implicitly trusted to inject. that's fine because the
bind-mount is the agent's own container; no new auth surface
opens up.

docs/turn-loop.md gets a new 'Waking the agent from inside
the container' section pointing at both paths (CLI + raw
JSON).

docs/turn-loop.md

@@ -112,6 +112,33 @@ it as a stdio child via `--mcp-config`. The hyperhive socket name is
   answer routes back to the asker's own inbox as
   `HelperEvent::OperatorAnswered` via `coord.notify_agent`.
 
+### Waking the agent from inside the container
+
+External MCP servers (and any other in-container process) can
+inject a wake-up event into the agent's inbox via the per-agent
+socket at `/run/hive/mcp.sock`. Two equivalent paths:
+
+- **Shell out to `hive-ag3nt wake --from <label> --body <text>`**
+  (use `--body -` to read body from stdin). Already on the
+  container's `PATH` since the harness binary is in
+  `systemPackages`. Convenient for shell-script integrations.
+
+- **Speak the wire protocol directly** — JSON-line over the
+  unix socket: `{"cmd":"wake","from":"matrix","body":"new dm
+  from @alice"}\n`. Same shape any other AgentRequest uses;
+  see `hive-sh4re::AgentRequest::Wake`.
+
+The wake event lands in the broker as `{from:<label>,
+to:<agent>, body}`, which wakes whatever `recv` call the
+harness is currently blocked on. Next turn fires with the
+wake prompt formed from that message — claude sees "from:
+matrix" (or whatever label) and reacts.
+
+Identity = socket: anything that can connect to
+`/run/hive/mcp.sock` is implicitly trusted to inject these,
+which is fine because the bind-mount is the agent's own
+container only.
+
 ### Extra MCP servers (per-agent)
 
 Each agent's NixOS config can declare additional MCP servers via