diff --git a/packages/server/src/server/agent/providers/omp/agent.test.ts b/packages/server/src/server/agent/providers/omp/agent.test.ts
index f06bb62f57..11eaa63fb7 100644
--- a/packages/server/src/server/agent/providers/omp/agent.test.ts
+++ b/packages/server/src/server/agent/providers/omp/agent.test.ts
@@ -927,6 +927,24 @@ describe("OMP agent client and session", () => {
     expect(omp.completedTurnCount()).toBe(1);
   });
 
+  test.each(["result after ack", "result before ack"] as const)(
+    "fails a prompt OMP rejects before its agent runs (%s)",
+    async (order) => {
+      const omp = new OmpHarness();
+      await omp.start();
+
+      await expect(
+        omp.runPromptRejectedBeforeAgentRuns(
+          "Reply with ok.",
+          "No API key found for anthropic.",
+          order,
+        ),
+      ).rejects.toThrow("No API key found for anthropic.");
+      expect(omp.turnFailures()).toEqual(["No API key found for anthropic."]);
+      expect(omp.completedTurnCount()).toBe(0);
+    },
+  );
+
   test("completes a no-turn notify with one notification and no assistant text", async () => {
     const scheduler = new ManualNoTurnScheduler();
     const omp = new OmpHarness({ noTurnScheduler: scheduler });
diff --git a/packages/server/src/server/agent/providers/omp/agent.ts b/packages/server/src/server/agent/providers/omp/agent.ts
index 4c97014fe8..b4e7b40bee 100644
--- a/packages/server/src/server/agent/providers/omp/agent.ts
+++ b/packages/server/src/server/agent/providers/omp/agent.ts
@@ -172,6 +172,21 @@ interface OmpPersistenceMetadata {
   bridgedTools: Map<string, OmpBridgedToolIdentity>;
 }
 
+/** OMP's outcome for one prompt, correlated by the prompt's request id. */
+interface OmpPromptResult {
+  agentInvoked: boolean;
+  /** Why OMP rejected the prompt before its agent ran, such as a missing API key. */
+  error: string | null;
+}
+
+function promptResultError(result: {
+  status?: string;
+  error?: { message: string };
+}): string | null {
+  if (result.status !== "error") return null;
+  return result.error?.message || "OMP rejected the prompt";
+}
+
 interface StartTurnResult {
   turnId: string;
 }
@@ -695,7 +710,8 @@ export class OmpAgentSession implements AgentSession {
   private readonly pendingNoTurnOutputs: Array<{ turnId: string; message: string }> = [];
   private activePromptRequestId: string | null = null;
   private activePromptAgentInvoked: boolean | null = null;
-  private readonly pendingPromptResults = new Map<string, boolean>();
+  private activePromptError: string | null = null;
+  private readonly pendingPromptResults = new Map<string, OmpPromptResult>();
   private pendingNoTurnCompletionAbort: AbortController | null = null;
   private lastKnownThinkingOptionId: string | null;
   private outOfBandCompactionEmit: ((event: AgentStreamEvent) => void) | null = null;
@@ -865,12 +881,13 @@ export class OmpAgentSession implements AgentSession {
         if (ack.requestId) {
           this.pendingPromptResults.delete(ack.requestId);
         }
-        this.activePromptAgentInvoked = correlatedResult ?? ack.agentInvoked ?? null;
-        if (correlatedResult === false) {
+        this.activePromptAgentInvoked = correlatedResult?.agentInvoked ?? ack.agentInvoked ?? null;
+        this.activePromptError = correlatedResult?.error ?? null;
+        if (correlatedResult?.agentInvoked === false) {
           this.scheduleNoTurnPromptCompletion(turnId);
           return;
         }
-        if (correlatedResult !== true && ack.agentInvoked === false) {
+        if (correlatedResult?.agentInvoked !== true && ack.agentInvoked === false) {
           await this.completeNoTurnPrompt(turnId);
           return;
         }
@@ -1309,7 +1326,14 @@ export class OmpAgentSession implements AgentSession {
     ) {
       return;
     }
+    const error = this.activePromptError;
     this.emitBufferedNoTurnOutputs(turnId);
+    if (error) {
+      this.usagePoller.stopTurn();
+      this.resetActiveTurn({ terminalizeWork: true });
+      this.emit({ type: "turn_failed", provider: this.provider, turnId, error });
+      return;
+    }
     this.completeTurn(turnId, []);
   }
 
@@ -1318,6 +1342,7 @@ export class OmpAgentSession implements AgentSession {
     this.activeNoTurnPromptText = null;
     this.activePromptRequestId = null;
     this.activePromptAgentInvoked = null;
+    this.activePromptError = null;
     this.pendingNoTurnOutputs.splice(0, this.pendingNoTurnOutputs.length);
   }
 
@@ -1715,15 +1740,17 @@ export class OmpAgentSession implements AgentSession {
           ? event.agentInvoked
           : undefined;
       if (requestId && agentInvoked !== undefined) {
+        const result = { agentInvoked, error: promptResultError(event) };
         if (requestId === this.activePromptRequestId && this.activeTurnId) {
           this.activePromptAgentInvoked = agentInvoked;
+          this.activePromptError = result.error;
           if (agentInvoked === false) {
             this.scheduleNoTurnPromptCompletion(this.activeTurnId);
           } else {
             this.cancelNoTurnPromptCompletion();
           }
         } else if (this.activePromptRequestId === null) {
-          this.pendingPromptResults.set(requestId, agentInvoked);
+          this.pendingPromptResults.set(requestId, result);
         }
       }
       return;
diff --git a/packages/server/src/server/agent/providers/omp/rpc-types.ts b/packages/server/src/server/agent/providers/omp/rpc-types.ts
index 4c69f2fbeb..42972b6d1e 100644
--- a/packages/server/src/server/agent/providers/omp/rpc-types.ts
+++ b/packages/server/src/server/agent/providers/omp/rpc-types.ts
@@ -480,6 +480,8 @@ export const OmpRuntimeEventSchema = z.discriminatedUnion("type", [
       type: z.literal("prompt_result"),
       id: z.string().optional(),
       agentInvoked: z.boolean().optional(),
+      status: z.string().optional(),
+      error: z.object({ message: z.string() }).passthrough().optional(),
     })
     .passthrough(),
   z.object({ type: z.literal("process_exit"), error: z.string() }).passthrough(),
diff --git a/packages/server/src/server/agent/providers/omp/test-utils/omp-harness.ts b/packages/server/src/server/agent/providers/omp/test-utils/omp-harness.ts
index f7f0039257..233a10984e 100644
--- a/packages/server/src/server/agent/providers/omp/test-utils/omp-harness.ts
+++ b/packages/server/src/server/agent/providers/omp/test-utils/omp-harness.ts
@@ -329,6 +329,31 @@ export class OmpHarness {
     return { completed: () => isCompleted, completion };
   }
 
+  async runPromptRejectedBeforeAgentRuns(
+    input: string,
+    error: string,
+    order: "result after ack" | "result before ack",
+  ): Promise<unknown> {
+    const session = this.requireSession();
+    const runtime = this.omp.latestSession();
+    runtime.promptAck = { requestId: "prompt-rejected" };
+    const rejection = {
+      type: "prompt_result",
+      id: "prompt-rejected",
+      agentInvoked: false,
+      status: "error",
+      sessionSettled: true,
+      error: { message: error, retryable: false },
+    } as const;
+    const promptStarted = runtime.nextPrompt();
+    const run = session.run(input);
+    if (order === "result before ack") runtime.emit(rejection);
+    await promptStarted;
+    await waitForImmediate();
+    if (order === "result after ack") runtime.emit(rejection);
+    return await run;
+  }
+
   async runPromptAfterCorrelatedTrueResult(
     input: string,
     output: string,