feat(plugin): add session agent resolver for subagent_type lookup

src/plugin/session-agent-resolver.ts

@@ -0,0 +1,36 @@
+import { log } from "../shared"
+
+interface SessionMessage {
+  info?: {
+    agent?: string
+    role?: string
+  }
+}
+
+type SessionClient = {
+  session: {
+    messages: (opts: { path: { id: string } }) => Promise<{ data?: SessionMessage[] }>
+  }
+}
+
+export async function resolveSessionAgent(
+  client: SessionClient,
+  sessionId: string,
+): Promise<string | undefined> {
+  try {
+    const messagesResp = await client.session.messages({ path: { id: sessionId } })
+    const messages = (messagesResp.data ?? []) as SessionMessage[]
+
+    for (const msg of messages) {
+      if (msg.info?.agent) {
+        return msg.info.agent
+      }
+    }
+  } catch (error) {
+    log("[session-agent-resolver] Failed to resolve agent from session", {
+      sessionId,
+      error: String(error),
+    })
+  }
+  return undefined
+}