fix(omp): wait for terminal event after custom messages (#3258)

Custom messages may precede the prompt user message during an active OMP turn. Treating them as completion terminalized the turn while the provider continued working.

Co-authored-by: paseo-bot[bot] <266920839+paseo-bot[bot]@users.noreply.github.com>

packages/server/src/server/agent/providers/omp/agent.test.ts

@@ -376,6 +376,25 @@ describe("OMP agent client and session", () => {
     expect(omp.completedTurnCount()).toBe(1);
   });
 
+  test("does not complete a turn when a custom message arrives before its user message", async () => {
+    const omp = new OmpHarness();
+    await omp.start();
+    await omp.requireStartTurn("hello OMP");
+
+    const runtime = omp.runtime();
+    runtime.beginTurn();
+    runtime.acceptCustomMessage("startup notice");
+
+    expect(omp.completedTurnCount()).toBe(0);
+
+    runtime.acceptPrompt("hello OMP", "user-1");
+    runtime.streamAssistantText("model turn completed");
+    runtime.finishTurn();
+    await waitForImmediate();
+
+    expect(omp.completedTurnCount()).toBe(1);
+  });
+
   test("omits live custom messages when display is false", async () => {
     const omp = new OmpHarness();
     await omp.start();

packages/server/src/server/agent/providers/omp/agent.ts

@@ -2033,9 +2033,6 @@ export class OmpAgentSession implements AgentSession {
           });
         }
       }
-      if (!this.activeTurnHasUserMessage) {
-        this.completeTurn(turnId, []);
-      }
       return;
     }