diff --git a/packages/server/src/server/agent/mcp-server.test.ts b/packages/server/src/server/agent/mcp-server.test.ts
index e695c84048..dbe0885d5c 100644
--- a/packages/server/src/server/agent/mcp-server.test.ts
+++ b/packages/server/src/server/agent/mcp-server.test.ts
@@ -3704,18 +3704,29 @@ class HeldTurnAgentSession implements AgentSession {
   readonly prompts: string[] = [];
   private readonly subscribers = new Set<(event: AgentStreamEvent) => void>();
   private activeTurnId: string | null = null;
+  private turnStartGate: Promise<void> | null = null;
 
   constructor(
     readonly provider: AgentProvider,
     private readonly holdTurns: boolean,
   ) {}
 
+  /** Hold the next turn's acknowledgment, as a provider awaiting its turn-start request does. */
+  holdTurnStart(): () => void {
+    let release!: () => void;
+    this.turnStartGate = new Promise((resolve) => {
+      release = resolve;
+    });
+    return release;
+  }
+
   async run(): Promise<AgentRunResult> {
     return { sessionId: this.id, finalText: "", timeline: [] };
   }
 
   async startTurn(prompt: AgentPromptInput): Promise<{ turnId: string }> {
     this.prompts.push(typeof prompt === "string" ? prompt : JSON.stringify(prompt));
+    await this.turnStartGate;
     const turnId = randomUUID();
     this.activeTurnId = turnId;
     setTimeout(() => {
@@ -4085,6 +4096,127 @@ describe("send_agent_prompt MCP tool", () => {
       await removeAgentStateDir(agentManager, storage, workdir);
     }
   });
+
+  it("reports a background prompt's accepted turn as running", async () => {
+    const workdir = await mkdtemp(join(tmpdir(), "mcp-background-send-status-"));
+    const storage = new AgentStorage(join(workdir, "agents"), logger);
+    const parentClient = new HeldTurnAgentClient("claude", false);
+    const childClient = new HeldTurnAgentClient("codex", true);
+    const agentManager = new AgentManager({
+      clients: { claude: parentClient, codex: childClient },
+      registry: storage,
+      logger,
+    });
+
+    try {
+      const parent = await agentManager.createAgent(
+        { provider: "claude", cwd: existingCwd },
+        undefined,
+        { workspaceId: "wks_parent" },
+      );
+      const child = await agentManager.createAgent(
+        { provider: "codex", cwd: existingCwd },
+        undefined,
+        { workspaceId: "wks_parent" },
+      );
+      const server = await createAgentMcpServer({
+        agentManager,
+        agentStorage: storage,
+        callerAgentId: parent.id,
+        providerSnapshotManager: createOpenCodeManager().manager,
+        logger,
+      });
+      const tool = registeredTool(server, "send_agent_prompt");
+      const childSession = childClient.sessions[0]!;
+      const acknowledgeTurnStart = childSession.holdTurnStart();
+
+      const pending = invokeToolWithParsedInput(tool, {
+        agentId: child.id,
+        prompt: "Follow up",
+      });
+      await vi.waitFor(() => expect(childSession.prompts).toEqual(["Follow up"]));
+      acknowledgeTurnStart();
+      const response = await pending;
+
+      expect(response.structuredContent).toMatchObject({ success: true, status: "running" });
+      expect(agentManager.getAgent(child.id)?.lifecycle).toBe("running");
+
+      childSession.finishTurn();
+      await vi.waitFor(() => {
+        const parentPrompts = parentClient.sessions[0]!.prompts;
+        expect(parentPrompts).toHaveLength(1);
+        expect(parentPrompts[0]).toContain(child.id);
+        expect(parentPrompts[0]).toContain("finished");
+      });
+    } finally {
+      await removeAgentStateDir(agentManager, storage, workdir);
+    }
+  });
+
+  it("accepts a background turn completed as the manager publishes its start", async () => {
+    const workdir = await mkdtemp(join(tmpdir(), "mcp-fast-background-send-"));
+    const storage = new AgentStorage(join(workdir, "agents"), logger);
+    const parentClient = new HeldTurnAgentClient("claude", false);
+    const childClient = new HeldTurnAgentClient("codex", true);
+    const agentManager = new AgentManager({
+      clients: { claude: parentClient, codex: childClient },
+      registry: storage,
+      logger,
+    });
+
+    try {
+      const parent = await agentManager.createAgent(
+        { provider: "claude", cwd: existingCwd },
+        undefined,
+        { workspaceId: "wks_parent" },
+      );
+      const child = await agentManager.createAgent(
+        { provider: "codex", cwd: existingCwd },
+        undefined,
+        { workspaceId: "wks_parent" },
+      );
+      const server = await createAgentMcpServer({
+        agentManager,
+        agentStorage: storage,
+        callerAgentId: parent.id,
+        providerSnapshotManager: createOpenCodeManager().manager,
+        logger,
+      });
+      let finished = false;
+      const unsubscribe = agentManager.subscribe(
+        (event) => {
+          if (
+            !finished &&
+            event.type === "agent_state" &&
+            event.agent.id === child.id &&
+            event.agent.lifecycle === "running"
+          ) {
+            finished = true;
+            childClient.sessions[0]!.finishTurn();
+          }
+        },
+        { agentId: child.id, replayState: false },
+      );
+
+      const response = await invokeToolWithParsedInput(
+        registeredTool(server, "send_agent_prompt"),
+        {
+          agentId: child.id,
+          prompt: "Fast reply",
+        },
+      );
+      unsubscribe();
+      expect(response.structuredContent).toMatchObject({ success: true, status: "idle" });
+      await vi.waitFor(() => {
+        const parentPrompts = parentClient.sessions[0]!.prompts;
+        expect(parentPrompts).toHaveLength(1);
+        expect(parentPrompts[0]).toContain(child.id);
+        expect(parentPrompts[0]).toContain("finished");
+      });
+    } finally {
+      await removeAgentStateDir(agentManager, storage, workdir);
+    }
+  });
 });
 
 describe("update_agent MCP tool", () => {
diff --git a/packages/server/src/server/agent/tools/paseo-tools.ts b/packages/server/src/server/agent/tools/paseo-tools.ts
index 6ad1c60574..07f9f21098 100644
--- a/packages/server/src/server/agent/tools/paseo-tools.ts
+++ b/packages/server/src/server/agent/tools/paseo-tools.ts
@@ -61,7 +61,11 @@ import {
   toScheduleSummary,
   waitForAgentWithTimeout,
 } from "../mcp-shared.js";
-import { sendPromptToAgent, setupFinishNotification } from "../agent-prompt.js";
+import {
+  sendPromptToAgent,
+  setupFinishNotification,
+  waitForAgentRunStartWithTimeout,
+} from "../agent-prompt.js";
 import { respondToAgentPermission } from "../permission-response.js";
 import {
   archiveAgentCommand,
@@ -1924,7 +1928,7 @@ export function createPaseoToolCatalog(options: PaseoToolHostDependencies): Pase
         return true;
       }
 
-      await sendPromptToAgent({
+      const { disposition } = await sendPromptToAgent({
         agentManager,
         agentStorage,
         agentId,
@@ -1963,8 +1967,10 @@ export function createPaseoToolCatalog(options: PaseoToolHostDependencies): Pase
 
       const notifying = armFinishNotification();
 
-      // Return immediately if background=true
-      // Re-fetch snapshot since the state may have changed
+      // Return once the provider has accepted the turn, so the status reports it running.
+      if (disposition === "turn_started") {
+        await waitForAgentRunStartWithTimeout(agentManager, agentId);
+      }
       const currentSnapshot = agentManager.getAgent(agentId);
 
       const responseData = {