diff --git a/packages/server/src/server/agent/providers/claude/agent.test.ts b/packages/server/src/server/agent/providers/claude/agent.test.ts
index ecfc29cd30..7ed7d359e5 100644
--- a/packages/server/src/server/agent/providers/claude/agent.test.ts
+++ b/packages/server/src/server/agent/providers/claude/agent.test.ts
@@ -867,6 +867,34 @@ describe("ClaudeAgentSession features", () => {
     await session.close();
   });
 
+  test("applying options before the first query keeps the session's restrictions", async () => {
+    const { queryFactory } = createQueryMock();
+    const client = new ClaudeAgentClient({
+      logger,
+      queryFactory,
+      resolveBinary: async () => "/test/claude/bin",
+    });
+    const session = await client.createSession({
+      provider: "claude",
+      cwd: process.cwd(),
+      model: "claude-opus-4-8",
+      providerOptions: {
+        disallowedTools: ["Bash"],
+        sandbox: { enabled: true, failIfUnavailable: true },
+      },
+    });
+
+    // The manager hands the session only the agent's own options.
+    await session.applyOptions?.({ fast_mode: true });
+    await (session as unknown as { ensureQuery(): Promise<unknown> }).ensureQuery();
+
+    expect(queryFactory.mock.calls[0]?.[0].options).toMatchObject({
+      disallowedTools: ["Bash"],
+      sandbox: { enabled: true, failIfUnavailable: true },
+    });
+    await session.close();
+  });
+
   test("passes extra Claude Code CLI arguments to the SDK", async () => {
     const { queryFactory, launches } = createQueryMock();
     const client = new ClaudeAgentClient({
diff --git a/packages/server/src/server/agent/providers/claude/agent.ts b/packages/server/src/server/agent/providers/claude/agent.ts
index de70858db5..6d483aa2b6 100644
--- a/packages/server/src/server/agent/providers/claude/agent.ts
+++ b/packages/server/src/server/agent/providers/claude/agent.ts
@@ -2800,9 +2800,10 @@ class ClaudeAgentSession implements AgentSession {
   async applyOptions(options: ProviderOptions): Promise<void> {
     const providerOptions =
       validateProviderOptions("claude", ClaudeProviderOptionsSchema, options) ?? {};
+    // Supplied keys update the running options; absent keys keep their running value.
+    const running = { ...this.config.providerOptions, ...providerOptions };
     const hadFast = this.config.providerOptions.fast_mode === true;
-    // An absent option leaves Fast as it is; only an explicit value changes it.
-    const wantsFast = providerOptions.fast_mode === undefined ? hadFast : providerOptions.fast_mode;
+    const wantsFast = running.fast_mode === true;
     const modelSupportsFast = claudeModelSupportsFastMode(this.config.model);
     if (wantsFast && !hadFast && !modelSupportsFast) {
       throw new Error(
@@ -2817,7 +2818,7 @@ class ClaudeAgentSession implements AgentSession {
       this.cachedRuntimeInfo = null;
     }
     // Held until the runtime accepts, so a rejected change is retried instead of skipped.
-    this.config.providerOptions = { ...providerOptions, ...(wantsFast ? { fast_mode: true } : {}) };
+    this.config.providerOptions = running;
   }
 
   getPendingPermissions(): AgentPermissionRequest[] {
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 01c2b87ce9..d01fe5e739 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
@@ -559,6 +559,18 @@ describe("Codex app-server provider controls", () => {
     });
   });
 
+  test("an explicit tier still beats a legacy fast_mode on a patch that supplies neither", async () => {
+    const { session, appServer } = await createConnectedSession({
+      providerOptions: { service_tier: "default", fast_mode: true },
+    });
+
+    // The manager hands the session only the agent's own options.
+    await session.applyOptions?.({ fast_mode: true, plan_mode: true });
+    await session.startTurn("hello");
+
+    await expect(appServer.waitForTurnStart()).resolves.toMatchObject({ serviceTier: "default" });
+  });
+
   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 40315c05b3..052fca7cc7 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
@@ -4661,8 +4661,11 @@ export class CodexAppServerAgentSession implements AgentSession {
   async applyOptions(options: ProviderOptions): Promise<void> {
     const next = validateProviderOptions("codex", CodexProviderOptionsSchema, options) ?? {};
     // An absent speed or plan option leaves the session as it is.
+    // Supplied keys update the running options; absent keys keep their running value, so an
+    // explicit tier still beats a legacy `fast_mode` on a patch that supplies neither.
+    const running = { ...this.providerOptions, ...next };
     const speedGiven = next.service_tier !== undefined || next.fast_mode !== undefined;
-    const requestedTier = speedGiven ? readCodexServiceTier(next) : this.requestedServiceTier;
+    const requestedTier = speedGiven ? readCodexServiceTier(running) : this.requestedServiceTier;
     if (
       requestedTier !== this.requestedServiceTier &&
       !this.isServiceTierAvailable(requestedTier)
@@ -4671,8 +4674,7 @@ export class CodexAppServerAgentSession implements AgentSession {
         `Codex speed '${String(requestedTier)}' is not available for model '${this.config.model ?? "default"}'`,
       );
     }
-    // Supplied keys update the running options; absent keys keep their running value.
-    this.providerOptions = { ...this.providerOptions, ...next };
+    this.providerOptions = running;
     this.requestedServiceTier = requestedTier;
     this.setPlanMode(next.plan_mode === undefined ? this.planModeEnabled : next.plan_mode === true);
     this.cachedRuntimeInfo = null;