fix(server): stream a prompt Pi queued after the server turn ended

packages/server/src/harness/pi/process.ts

@@ -559,11 +559,17 @@ export const makePiProcessWithDependencies = <R>(
                         output: Stream.empty,
                       };
                     }
-                    return yield* new AgentOperationError({
-                      sessionId: input.sessionId,
-                      operation: "prompt-admission-state",
-                      cause: new Error("Pi queued a prompt without an active server turn"),
-                    });
+                    // Extension command already ran. No model turn follows.
+                    if (admission?.disposition === "handled") {
+                      return {
+                        turnId: uuid(),
+                        started: false,
+                        output: Stream.empty,
+                      };
+                    }
+                    // Pi queued this prompt while we have no turn (its run
+                    // outlived the finish we already consumed). Attach and
+                    // stream that run instead of failing the RPC.
                   }
 
                   const previous = yield* Ref.get(session.turnState);

packages/server/src/harness/pi/rpc/rpc-mode.ts

@@ -445,7 +445,12 @@ export async function runRpcMode(runtimeHost: AgentSessionRuntime): Promise<neve
               // 0.99 reports disposition instead of a boolean. isStreaming is
               // already true for a prompt that just started, so it cannot mean
               // "queued".
-              output(success(id, "prompt", { started: disposition === "started" }));
+              output(
+                success(id, "prompt", {
+                  started: disposition === "started",
+                  disposition,
+                }),
+              );
             },
           })
           .catch((cause: unknown) => {

packages/server/src/harness/pi/rpc/rpc-types.ts

@@ -144,7 +144,7 @@ export type RpcResponse =
       type: "response";
       command: "prompt";
       success: true;
-      data: { started: boolean };
+      data: { started: boolean; disposition?: "started" | "queued" | "handled" };
     }
   | { id?: string; type: "response"; command: "steer"; success: true }
   | { id?: string; type: "response"; command: "follow_up"; success: true }

packages/server/test/harness/pi/agent.test.ts

@@ -94,6 +94,22 @@ rl.on("line", (line) => {
   if (msg.type !== "prompt") return;
   const text = msg.message;
   if (text === "fail") { send({ id: msg.id, type: "response", command: "prompt", success: false, error: "cannot prompt" }); return; }
+  if (text === "queue-idle") {
+    send({ id: msg.id, type: "response", command: "prompt", success: true, data: { started: false, disposition: "queued" } });
+    send({ type: "agent_start" });
+    send({ type: "message_start", message: assistant() });
+    upd({ type: "start" });
+    upd({ type: "text_start", contentIndex: 0 });
+    upd({ type: "text_delta", contentIndex: 0, delta: "queued" });
+    upd({ type: "text_end", contentIndex: 0, content: "queued" });
+    send({ type: "message_end", message: assistant() });
+    settle();
+    return;
+  }
+  if (text === "handled") {
+    send({ id: msg.id, type: "response", command: "prompt", success: true, data: { started: false, disposition: "handled" } });
+    return;
+  }
   if (holding && !msg.streamingBehavior) {
     send({ id: msg.id, type: "response", command: "prompt", success: false, error: "Agent is already processing. Specify streamingBehavior ('steer' or 'followUp') to queue the message." });
     return;
@@ -192,6 +208,41 @@ layer(NodeServices.layer)("PiAgent", (it) => {
     }),
   );
 
+  it.effect("streams a prompt Pi queued while the server has no turn", () =>
+    Effect.gen(function* () {
+      const agent = yield* makePiProcess({ executable: { command: makeFake(), prefixArgs: [] } });
+      const { sessionId } = yield* agent.session.create({ cwd: "/tmp" });
+      const prompt = yield* agent.session.prompt({ sessionId, text: "queue-idle" });
+      assert.equal(prompt.started, true);
+      const chunks = yield* Stream.runCollect(prompt.output);
+      assert.deepEqual(
+        Array.from(chunks, (chunk) => chunk.type),
+        [
+          "start",
+          "message-metadata",
+          "text-start",
+          "text-delta",
+          "text-end",
+          "message-metadata",
+          "finish",
+        ],
+      );
+      yield* agent.session.abort(sessionId);
+    }),
+  );
+
+  it.effect("accepts a handled prompt without opening a turn", () =>
+    Effect.gen(function* () {
+      const agent = yield* makePiProcess({ executable: { command: makeFake(), prefixArgs: [] } });
+      const { sessionId } = yield* agent.session.create({ cwd: "/tmp" });
+      const prompt = yield* agent.session.prompt({ sessionId, text: "handled" });
+      assert.equal(prompt.started, false);
+      const chunks = yield* Stream.runCollect(prompt.output);
+      assert.equal(Array.from(chunks).length, 0);
+      yield* agent.session.abort(sessionId);
+    }),
+  );
+
   it.effect("resume keeps the caller-provided session id", () =>
     Effect.gen(function* () {
       const agent = yield* makePiProcess({ executable: { command: makeFake(), prefixArgs: [] } });