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 38a54294b2..a70c017b4c 100644
--- a/packages/server/src/server/agent/providers/omp/agent.test.ts
+++ b/packages/server/src/server/agent/providers/omp/agent.test.ts
@@ -780,6 +780,18 @@ describe("OMP agent client and session", () => {
     expect(omp.runtime().setFastModeRequests).toEqual([]);
   });
 
+  test("a replacement runtime that refuses the Fast the session had publishes what it accepted", async () => {
+    const omp = new OmpHarness();
+    omp.acceptFastOnNextRuntime();
+    await omp.start({ modeId: "full", providerOptions: { fast_mode: true } });
+    expect(omp.requireSession().openOptionsPatch).toEqual({});
+
+    // The approval-mode restart starts a second runtime, which refuses Fast.
+    await omp.setMode("ask");
+
+    expect(omp.optionsChanges()).toEqual([{ fast_mode: false }]);
+  });
+
   test("restores Fast from the initial OMP state on create and resume", async () => {
     const created = new OmpHarness();
     await created.start({ providerOptions: { fast_mode: true } });
diff --git a/packages/server/src/server/agent/providers/omp/agent.ts b/packages/server/src/server/agent/providers/omp/agent.ts
index 7fe3e517fa..149e7d475e 100644
--- a/packages/server/src/server/agent/providers/omp/agent.ts
+++ b/packages/server/src/server/agent/providers/omp/agent.ts
@@ -1095,6 +1095,7 @@ export class OmpAgentSession implements AgentSession {
       const old = this.runtimeSession;
       const oldHostTools = this.hostTools;
       const previousSessionId = this.state.sessionId;
+      const fastModeBefore = this.state.fastModeEnabled;
       const restarted = await this.restartRuntime(
         this.config.internal ? null : (this.state.sessionFile ?? null),
         modeId,
@@ -1115,6 +1116,7 @@ export class OmpAgentSession implements AgentSession {
         this.config.modeId = modeId;
         this.runtimeDead = false;
         this.attachRuntime(next);
+        this.publishFastModeChange(fastModeBefore);
         this.subagentIndex.clear(old);
         await oldHostTools?.close();
         await old.close().catch(() => undefined);
@@ -2267,6 +2269,11 @@ export class OmpAgentSession implements AgentSession {
   private async refreshState(): Promise<void> {
     const before = this.state.fastModeEnabled;
     this.state = await this.runtimeSession.getState();
+    this.publishFastModeChange(before);
+  }
+
+  // The runtime owns Fast: whatever it accepted is what the session now runs with.
+  private publishFastModeChange(before: boolean | undefined): void {
     if (this.state.fastModeEnabled !== before && typeof this.state.fastModeEnabled === "boolean") {
       this.rememberFastMode(this.state.fastModeEnabled);
       this.emit({
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 8be53f1742..8aeaa50312 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
@@ -467,6 +467,16 @@ export class OmpHarness {
     return this.events.map((event) => event.type);
   }
 
+  acceptFastOnNextRuntime(): void {
+    this.omp.queueSessionSetup((runtime) => {
+      runtime.fastModeResult = { enabled: true, active: true };
+    });
+  }
+
+  optionsChanges(): Record<string, unknown>[] {
+    return this.events.flatMap((event) => (event.type === "options_changed" ? [event.patch] : []));
+  }
+
   async history(): Promise<AgentTimelineItem[]> {
     const items: AgentTimelineItem[] = [];
     for await (const event of this.requireSession().streamHistory()) {