diff --git a/packages/server/src/server/agent/agent-manager.test.ts b/packages/server/src/server/agent/agent-manager.test.ts
index 347954a787..f8fc24a7f4 100644
--- a/packages/server/src/server/agent/agent-manager.test.ts
+++ b/packages/server/src/server/agent/agent-manager.test.ts
@@ -12831,6 +12831,55 @@ describe("agent options", () => {
     ]);
   });
 
+  test("after a removal the snapshot shows the live setting, not the configured default", async () => {
+    class LiveSession extends OptionsSession {
+      private tier = "priority";
+      override async applyOptions(options: ProviderOptions): Promise<void> {
+        await super.applyOptions(options);
+        if (typeof options.service_tier === "string") this.tier = options.service_tier;
+      }
+      get controls(): AgentOptionControl[] {
+        return [
+          {
+            type: "select",
+            key: "service_tier",
+            label: "Speed",
+            defaultValue: this.tier,
+            choices: [
+              { value: "default", label: "Normal" },
+              { value: "priority", label: "Fast" },
+            ],
+          },
+        ];
+      }
+    }
+    class LiveClient extends OptionsClient {
+      override async createSession(config: AgentSessionConfig): Promise<AgentSession> {
+        return new LiveSession(config);
+      }
+    }
+    const workdir = mkdtempSync(join(tmpdir(), "agent-manager-options-"));
+    const manager = new AgentManager({
+      clients: { codex: new LiveClient() },
+      registry: new AgentStorage(join(workdir, "agents"), logger),
+      logger,
+    });
+    const created = await manager.createAgent(
+      { provider: "codex", cwd: workdir, providerOptions: { service_tier: "priority" } },
+      undefined,
+      { workspaceId: undefined },
+    );
+
+    await manager.setAgentOptions(created.id, { service_tier: null });
+
+    const agent = manager.getAgent(created.id)!;
+    expect(agent.config.providerOptions).toBeUndefined();
+    expect(toAgentPayload(agent).options).toEqual({ service_tier: "priority" });
+    expect(toAgentPayload(agent).features).toEqual([
+      expect.objectContaining({ id: "service_tier", value: "priority" }),
+    ]);
+  });
+
   test("an option without a control is settable through the patch and readable in the snapshot", async () => {
     const { manager, client, storage, agentId } = await createOptionsAgent();
 
diff --git a/packages/server/src/server/agent/agent-manager.ts b/packages/server/src/server/agent/agent-manager.ts
index f82eae0665..d9968df48b 100644
--- a/packages/server/src/server/agent/agent-manager.ts
+++ b/packages/server/src/server/agent/agent-manager.ts
@@ -5274,7 +5274,17 @@ export class AgentManager {
     if ("session" in agent && agent.session?.controls) {
       agent.controls = agent.session.controls;
     }
-    agent.effectiveOptions = this.effectiveOptionsFor(agent.provider, agent.config.providerOptions);
+    const own = agent.config.providerOptions;
+    const effective = { ...this.effectiveOptionsFor(agent.provider, own) };
+    // After a removal the running provider keeps its setting, so a control it reports for a key
+    // the agent no longer holds shows that live value rather than the `config.json` default.
+    for (const control of agent.controls ?? []) {
+      const live = control.defaultValue;
+      if (own?.[control.key] === undefined && control.key in effective && live !== undefined) {
+        effective[control.key] = live;
+      }
+    }
+    agent.effectiveOptions = effective;
   }
 
   private checkAndSetAttention(agent: ManagedAgent): void {
diff --git a/packages/server/src/server/agent/providers/codex-app-server-agent.features.test.ts b/packages/server/src/server/agent/providers/codex-app-server-agent.features.test.ts
index be3af8332f..01c2b87ce9 100644
--- a/packages/server/src/server/agent/providers/codex-app-server-agent.features.test.ts
+++ b/packages/server/src/server/agent/providers/codex-app-server-agent.features.test.ts
@@ -533,6 +533,32 @@ describe("Codex app-server provider controls", () => {
     await expect(session.applyOptions?.({ sandbox_mode: "read-only" })).resolves.toBeUndefined();
   });
 
+  test("applying unrelated options keeps the running sandbox", async () => {
+    const { session, appServer } = await createConnectedSession({
+      providerOptions: { sandbox_mode: "read-only" },
+    });
+
+    await session.applyOptions?.({ plan_mode: true });
+    await session.startTurn("hello");
+
+    await expect(appServer.waitForTurnStart()).resolves.toMatchObject({
+      sandboxPolicy: { type: "readOnly" },
+    });
+  });
+
+  test("removing the sandbox option keeps the running sandbox", async () => {
+    const { session, appServer } = await createConnectedSession({
+      providerOptions: { sandbox_mode: "read-only" },
+    });
+
+    await session.applyOptions?.({});
+    await session.startTurn("hello");
+
+    await expect(appServer.waitForTurnStart()).resolves.toMatchObject({
+      sandboxPolicy: { type: "readOnly" },
+    });
+  });
+
   test("startTurn includes serviceTier when fast mode is enabled", async () => {
     const { session, appServer } = await createConnectedSession();
 
diff --git a/packages/server/src/server/agent/providers/codex-app-server-agent.ts b/packages/server/src/server/agent/providers/codex-app-server-agent.ts
index 4e4e63d046..40315c05b3 100644
--- a/packages/server/src/server/agent/providers/codex-app-server-agent.ts
+++ b/packages/server/src/server/agent/providers/codex-app-server-agent.ts
@@ -4671,7 +4671,8 @@ export class CodexAppServerAgentSession implements AgentSession {
         `Codex speed '${String(requestedTier)}' is not available for model '${this.config.model ?? "default"}'`,
       );
     }
-    this.providerOptions = next;
+    // Supplied keys update the running options; absent keys keep their running value.
+    this.providerOptions = { ...this.providerOptions, ...next };
     this.requestedServiceTier = requestedTier;
     this.setPlanMode(next.plan_mode === undefined ? this.planModeEnabled : next.plan_mode === true);
     this.cachedRuntimeInfo = null;