fix(team-mode): register spawned sessions early

src/features/background-agent/manager.ts

@@ -580,6 +580,7 @@ export class BackgroundManager {
       return
     }
 
+    await input.onSessionCreated?.(sessionID)
     this.settlePreStartDescendantReservation(task)
     subagentSessions.add(sessionID)
 

src/features/background-agent/session-created-callback.test.ts

@@ -0,0 +1,65 @@
+/// <reference types="bun-types" />
+
+import { describe, expect, test } from "bun:test"
+import { tmpdir } from "node:os"
+
+import type { PluginInput } from "@opencode-ai/plugin"
+
+import { BackgroundManager } from "./manager"
+
+async function waitForEvent(events: readonly string[], eventName: string): Promise<void> {
+  const deadlineAt = Date.now() + 1_000
+  while (!events.includes(eventName)) {
+    if (Date.now() > deadlineAt) {
+      throw new Error(`timed out waiting for ${eventName}`)
+    }
+    await new Promise((resolve) => setTimeout(resolve, 10))
+  }
+}
+
+describe("BackgroundManager session created callback", () => {
+  test("fires onSessionCreated before the launch prompt is sent", async () => {
+    //#given
+    const events: string[] = []
+    const client = {
+      session: {
+        get: async ({ path }: { path: { id: string } }) => ({
+          data: { id: path.id, directory: tmpdir() },
+        }),
+        create: async () => {
+          events.push("session.create")
+          return { data: { id: "child-session" } }
+        },
+        promptAsync: async () => {
+          events.push("promptAsync")
+          return { data: {} }
+        },
+      },
+    }
+    const manager = new BackgroundManager({
+      pluginContext: { client, directory: tmpdir() } as PluginInput,
+    })
+
+    //#when
+    await manager.launch({
+      description: "Create child",
+      prompt: "Do work",
+      agent: "general",
+      parentSessionId: "parent-session",
+      parentMessageId: "parent-message",
+      onSessionCreated: (sessionId) => {
+        events.push(`onSessionCreated:${sessionId}`)
+      },
+    })
+    await waitForEvent(events, "promptAsync")
+
+    //#then
+    expect(events).toEqual([
+      "session.create",
+      "onSessionCreated:child-session",
+      "promptAsync",
+    ])
+
+    manager.shutdown()
+  })
+})

src/features/background-agent/spawner.ts

@@ -112,6 +112,7 @@ export async function startTask(
   }
 
   const sessionID = createResult.data.id
+  await input.onSessionCreated?.(sessionID)
   subagentSessions.add(sessionID)
 
   task.status = "running"

src/features/background-agent/types.ts

@@ -117,6 +117,7 @@ export interface LaunchInput {
   skillContent?: string
   category?: string
   sessionPermission?: SessionPermissionRule[]
+  onSessionCreated?: (sessionId: string) => void | Promise<void>
 }
 
 export interface ResumeInput {