fix(server): a saved legacy Codex Fast preference wins over a configured service_tier default

The defaults merge put a configured service_tier next to the agent's own legacy fast_mode, and Codex reads service_tier first, so the agent opened Normal. The agent's own alias now replaces the default of the key it stands for.

packages/server/src/server/agent/provider-options.ts

@@ -99,6 +99,31 @@ export function mergeProviderOptions(
   return merged;
 }
 
+// COMPAT(codexFastPreference): added in v0.10.0, remove after 2027-03-29 once saved Fast preferences have migrated.
+const LEGACY_OPTION_ALIASES: Record<string, Record<string, string>> = {
+  codex: { fast_mode: "service_tier" },
+};
+
+/**
+ * The options a provider opens with: `defaults` from config.json under the agent's `own`
+ * options. An agent's own legacy alias (a saved `fast_mode`) replaces the default of the key it
+ * stands for, so a configured `service_tier` does not override the agent's own Fast preference.
+ */
+export function mergeDefaultsUnderOwn(input: {
+  provider: string;
+  defaults: ProviderOptions | undefined;
+  own: ProviderOptions | undefined;
+}): ProviderOptions | undefined {
+  const { defaults, own } = input;
+  const aliases = LEGACY_OPTION_ALIASES[input.provider];
+  if (!aliases || !defaults || !own) return mergeProviderOptions(defaults, own);
+  const kept = { ...defaults };
+  for (const [alias, canonical] of Object.entries(aliases)) {
+    if (own[alias] !== undefined && own[canonical] === undefined) delete kept[canonical];
+  }
+  return mergeProviderOptions(kept, own);
+}
+
 function isPlainObject(value: unknown): value is ProviderOptions {
   if (value === null || typeof value !== "object") return false;
   const prototype = Object.getPrototypeOf(value);

packages/server/src/server/agent/provider-registry.test.ts

@@ -791,6 +791,24 @@ test("ACP provider configuration retains opaque options", () => {
   });
 });
 
+test("a saved legacy Codex Fast preference wins over a configured service_tier default", () => {
+  const registry = buildProviderRegistry(logger, {
+    providerOverrides: { codex: { options: { service_tier: "default", plan_mode: false } } },
+  });
+  const client = registry.codex.createClient(logger);
+
+  // Pre-v0.10 agents saved `fast_mode`; the agent's own preference beats the configured default.
+  expect(client.effectiveOptions?.({ fast_mode: true })).toEqual({
+    fast_mode: true,
+    plan_mode: false,
+  });
+  expect(client.effectiveOptions?.({ service_tier: "fast" })).toEqual({
+    service_tier: "fast",
+    plan_mode: false,
+  });
+  expect(client.effectiveOptions?.({})).toEqual({ service_tier: "default", plan_mode: false });
+});
+
 test("cursor provider extending acp uses CursorACPAgentClient", () => {
   const registry = buildProviderRegistry(logger, {
     providerOverrides: {

packages/server/src/server/agent/provider-registry.ts

@@ -48,7 +48,7 @@ import { PiRpcAgentClient } from "./providers/pi/agent.js";
 import { TraeACPAgentClient } from "./providers/trae-acp-agent.js";
 import { MockLoadTestAgentClient } from "./providers/mock-load-test-agent.js";
 import { MockSlowProviderClient } from "./providers/mock-slow-provider.js";
-import { ToolPolicyUnsupportedError, mergeProviderOptions } from "./provider-options.js";
+import { ToolPolicyUnsupportedError, mergeDefaultsUnderOwn } from "./provider-options.js";
 import {
   AGENT_PROVIDER_DEFINITIONS,
   BUILTIN_PROVIDER_IDS,
@@ -498,6 +498,8 @@ function wrapClientProvider(
   const archiveNativeSession = inner.archiveNativeSession?.bind(inner);
   const unarchiveNativeSession = inner.unarchiveNativeSession?.bind(inner);
   const configuredModelIds = [...profileModels, ...additionalModels].map((model) => model.id);
+  const withDefaults = (own: ProviderOptions | undefined) =>
+    mergeDefaultsUnderOwn({ provider: inner.provider, defaults: providerOptions, own });
 
   return {
     provider,
@@ -512,7 +514,7 @@ function wrapClientProvider(
           {
             ...config,
             provider: inner.provider,
-            providerOptions: mergeProviderOptions(providerOptions, config.providerOptions),
+            providerOptions: withDefaults(config.providerOptions),
           },
           launchContext,
           { ...options, configuredModelIds },
@@ -529,7 +531,7 @@ function wrapClientProvider(
           {
             ...overrides,
             provider: inner.provider,
-            providerOptions: mergeProviderOptions(providerOptions, overrides?.providerOptions),
+            providerOptions: withDefaults(overrides?.providerOptions),
           },
           launchContext,
           { ...options, configuredModelIds },
@@ -551,7 +553,7 @@ function wrapClientProvider(
             config: {
               ...config,
               provider: inner.provider,
-              providerOptions: mergeProviderOptions(providerOptions, config.providerOptions),
+              providerOptions: withDefaults(config.providerOptions),
             },
             env,
             signal,
@@ -560,13 +562,13 @@ function wrapClientProvider(
     resolveCreateConfig: inner.resolveCreateConfig?.bind(inner),
     resolveConfiguredModel: inner.resolveConfiguredModel?.bind(inner),
     isCreateConfigUnattended: inner.isCreateConfigUnattended?.bind(inner),
-    effectiveOptions: (own) => mergeProviderOptions(providerOptions, own) ?? {},
+    effectiveOptions: (own) => withDefaults(own) ?? {},
     listControls: listControls
       ? async (config) =>
           await listControls({
             ...config,
             provider: inner.provider,
-            providerOptions: mergeProviderOptions(providerOptions, config.providerOptions),
+            providerOptions: withDefaults(config.providerOptions),
           })
       : undefined,
     listImportableSessions: listImportableSessions
@@ -579,10 +581,7 @@ function wrapClientProvider(
             config: {
               ...context.config,
               provider: inner.provider,
-              providerOptions: mergeProviderOptions(
-                providerOptions,
-                context.config.providerOptions,
-              ),
+              providerOptions: withDefaults(context.config.providerOptions),
             },
             storedConfig: {
               ...context.storedConfig,