swarm: show subagent terminals in the swarm UI

An agent's subagent daemon publishes each subagent's output as terminal
rows on `$SWARM.term.<agent>.sub.<subagent>`, as the agent, into a
per-agent stream it creates itself; swarm-controller lists an agent's
subagents from that stream's subjects and relays one subagent's rows as
SSE; the swarm UI lists them under the agent's terminal preview and
reuses AgentTermPreview, full-screen tab included, with no input.

- swarm-nats.nix: the agent token may also publish
  `$SWARM.term.{agent}.sub.>` and `$JS.API.STREAM.CREATE|INFO` on
  `term-sub-{agent}`, and nothing else of JetStream. A module-eval arm
  pins the agent-token grant as an exact list.
- mcp.nix: hive-subagent-daemon loads the agent's store identity
  (`hive-agent-bao-cert/-key/-server-ca`, the ones hive-agent loads)
  whenever the agent has a store, not only on the opencode preset. The
  agent's own queue secret lives in the store, so this is the credential
  the harness connects with.
- hive-subagent-mcp: `swarm_term` reads the agent's queue secret under
  that identity, connects with the agent token, opens or creates
  `term-sub-<agent>` (max_age 24h), and publishes classified rows from
  the sink every subagent line already passes through. The sink only
  queues (bounded, drop-and-count); a missing store, refused credential,
  failed stream create or failed publish is a log line.
- The stream-json classifier (`stream_enrich`) and the `TermMsg` row
  types plus `fit` move from the hive-agent binary into hive-sh4re, so
  the subagent daemon publishes the rows AgentTermPreview already
  renders. hive-agent keeps its LiveEvent classifier on top.
- swarm-controller: `GET /api/agents/{name}/subagents` and
  `GET /api/agents/{name}/subagents/{subagent}/term/stream`.
- docs/swarm: what the UI shows and what the queue carries.

Closes #4827

swarm-controller/src/main.rs

@@ -58,6 +58,7 @@ mod queue_identity;
 mod read_policy;
 mod status;
 mod store;
+mod subagent_term;
 mod term_stream;
 mod vcs_metrics;
 mod wanted;
@@ -2992,6 +2993,8 @@ fn build_app(state: AppState) -> axum::Router {
         .routes(routes!(linked_accounts::get_linked_accounts))
         .routes(routes!(get_hive_wanted))
         .routes(routes!(term_stream::stream_agent_term))
+        .routes(routes!(subagent_term::list_subagents))
+        .routes(routes!(subagent_term::stream_subagent_term))
         .routes(routes!(agent_state_stream::stream_agent_state))
         .routes(routes!(issue_report::get_repos))
         .routes(routes!(issue_report::get_issue_report_all))
@@ -4981,6 +4984,55 @@ mod tests {
             "{problem:?}"
         );
     }
+
+    #[tokio::test]
+    async fn listing_subagents_needs_a_queue_and_an_identifier() {
+        let (state, _sched) = state_with_roster();
+        let no_queue = super::subagent_term::list_subagents(
+            axum::extract::State(state.clone()),
+            axum::extract::Path("iris".to_owned()),
+        )
+        .await
+        .expect_err("no queue is configured");
+        assert_eq!(
+            no_queue.status,
+            Some(axum::http::StatusCode::SERVICE_UNAVAILABLE),
+            "{no_queue:?}"
+        );
+        let bad_name = super::subagent_term::list_subagents(
+            axum::extract::State(state),
+            axum::extract::Path("iris.sub".to_owned()),
+        )
+        .await
+        .expect_err("a dot would widen the subject");
+        assert_eq!(
+            bad_name.status,
+            Some(axum::http::StatusCode::BAD_REQUEST),
+            "{bad_name:?}"
+        );
+    }
+
+    /// A subagent name is a subject token, so a wildcard or a dot in it is
+    /// refused before anything subscribes.
+    #[tokio::test]
+    async fn a_subagent_stream_refuses_a_name_that_is_not_one_token() {
+        let (state, _sched) = state_with_roster();
+        for subagent in ["*", ">", "a.b"] {
+            let Err(problem) = super::subagent_term::stream_subagent_term(
+                axum::extract::State(state.clone()),
+                axum::extract::Path(("iris".to_owned(), subagent.to_owned())),
+            )
+            .await
+            else {
+                panic!("{subagent:?} must be refused");
+            };
+            assert_eq!(
+                problem.status,
+                Some(axum::http::StatusCode::BAD_REQUEST),
+                "{subagent:?}: {problem:?}"
+            );
+        }
+    }
 }
 
 #[cfg(test)]