Show a session's subagents as subcards, each with a read-only transcript

A subagent is a second transcript owned by a session, in the same event
model, with no process and no controls. The claude translator routes lines
carrying parent_tool_use_id to a per-subagent translator and transcript
under <session>/subagents/<tool_use_id>; three routes expose the list, a
transcript page and the SSE stream. Echo grows /subagent [n] as the rig.

On the phone a card with subagents ends in a chevron expander, collapsed by
default, opening to outlined subcards styled like dev-updater's components;
a subcard opens SessionScreen in read-only form, addressed through
TranscriptAddress so paging, cache and stream are shared.

Design in SUBAGENTS.md; choices awaiting review in DECISIONS.md.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

app/androidApp/src/main/kotlin/com/example/aiapp/Api.kt

@@ -223,6 +223,14 @@ data class SessionSummary(
     val usageProvider: String?,
     val status: String,
     val lastActivity: Double,
+    /**
+     * How many subagents this session has, however their own status now reads.
+     *
+     * A directory listing on the server rather than a status read per subagent, so the list stays
+     * cheap; the per-subagent state is only fetched when the card is expanded. Zero on a server
+     * that predates subagents, so this app still opens against one.
+     */
+    val subagents: Int,
 )
 
 private fun parseSession(session: JSONObject) =
@@ -252,6 +260,7 @@ private fun parseSession(session: JSONObject) =
         usageProvider = session.optString("usageProvider").ifEmpty { null },
         status = session.getString("status"),
         lastActivity = session.getDouble("lastActivity"),
+        subagents = session.optInt("subagents", 0),
     )
 
 fun fetchSessions(settings: ServerSettings): List<SessionSummary> =
@@ -267,6 +276,35 @@ fun fetchSessions(settings: ServerSettings): List<SessionSummary> =
 fun fetchSession(settings: ServerSettings, sessionId: String): SessionSummary =
     requestFromServer(settings, "/sessions/$sessionId") { parseSession(it.jsonObject()) }
 
+/**
+ * One row of `GET /sessions/{id}/subagents`, oldest first.
+ *
+ * A subagent is a second transcript owned by a session -- no process, no controls of its own -- so
+ * this carries only what a card needs to draw and to open it; see SUBAGENTS.md. [status] is
+ * "running", "exited" or "unknown": a subagent whose session is not itself running cannot be
+ * running, and the list says so rather than reporting a state that cannot hold.
+ */
+data class SubagentSummary(
+    val id: String,
+    val title: String,
+    val status: String,
+    val created: Double,
+    val lastActivity: Double,
+)
+
+fun fetchSubagents(settings: ServerSettings, sessionId: String): List<SubagentSummary> =
+    requestFromServer(settings, "/sessions/$sessionId/subagents") {
+        it.jsonObjects { row ->
+            SubagentSummary(
+                id = row.getString("id"),
+                title = row.getString("title"),
+                status = row.getString("status"),
+                created = row.getDouble("created"),
+                lastActivity = row.getDouble("lastActivity"),
+            )
+        }
+    }
+
 // What the server offers, so the spawn screen has no hardcoded lists: a setup added to the server's
 // config.ron appears here with no app rebuild.
 //
@@ -968,7 +1006,7 @@ fun startImport(
  */
 fun fetchTranscript(
     settings: ServerSettings,
-    sessionId: String,
+    address: TranscriptAddress,
     before: Long? = null,
     limit: Int = 80,
     // Count [limit] in rows, not events, joining a reply's streamed deltas into one -- so a page of
@@ -987,7 +1025,7 @@ fun fetchTranscript(
         if (coalesce) append("&coalesce=true")
         if (after != null) append("&after=").append(after)
     }
-    return requestFromServer(settings, "/sessions/$sessionId/transcript$query") { connection ->
+    return requestFromServer(settings, "/${address.urlPath}/transcript$query") { connection ->
         val body = JSONArray(connection.inputStream.bufferedReader().readText())
         // The text as well as the event: the transcript cache stores the one and the fold needs the
         // other, and they have to be the same line.