Show a Fast-only speed as the Fast mode switch on mobile (#40523)

On the phone, Codex's Standard/Fast speed was a Speed row opening a
list while Claude's Fast mode was a switch. A Fast-only speed now uses
the same switch row; more speeds, or a lone Flex, keep the list. The
lone-Fast rule moves to shared code so desktop and mobile follow one
rule.

mobile/src/session/native-chat/input/MobileNativeChatSessionOptionPickers.test.ts

@@ -160,6 +160,31 @@ describe('MobileNativeChatSessionOptionPickers', () => {
     renderer = null
   })
 
+  it('toggles a Fast-only Codex speed on the same Fast mode switch as Claude', async () => {
+    const speed: SessionOptionDescriptor = {
+      id: 'serviceTier',
+      label: 'Speed',
+      kind: {
+        type: 'select',
+        currentValue: 'default',
+        choices: [
+          { value: 'default', label: 'Standard' },
+          { value: 'priority', label: 'Fast' }
+        ]
+      },
+      valueSource: 'reported',
+      transport: 'catalog',
+      settable: true
+    }
+    mount([MODEL_DESCRIPTOR, speed], false, 'model')
+    const toggle = findAllByHostType(renderer!.root, 'Switch').find(
+      (node) => node.props.accessibilityLabel === 'Fast mode'
+    )
+    expect(toggle?.props.value).toBe(false)
+    await act(async () => toggle!.props.onValueChange(true))
+    expect(setOption).toHaveBeenCalledWith('serviceTier', 'priority')
+  })
+
   it('consumes a refused page without replay, then permits a fresh open and permission pick', async () => {
     const placeholder: SessionOptionDescriptor = {
       ...MODEL_DESCRIPTOR,

mobile/src/session/native-chat/input/MobileNativeChatSessionOptionPickers.tsx

@@ -36,7 +36,8 @@ import {
   descriptorRowElements,
   ModelPill,
   SessionOptionCaption,
-  SessionOptionSummaryRow
+  SessionOptionSummaryRow,
+  showsSessionOptionAsSwitch
 } from './MobileNativeChatSessionOptionRows'
 import {
   SessionOptionSegments,
@@ -383,7 +384,7 @@ function OptionRows({
         {descriptors.flatMap((descriptor) => {
           const isPermission = descriptor === permission
           const disabled = locked(descriptor) || !descriptor.settable
-          if (descriptor.kind.type === 'boolean' && !descriptor.action) {
+          if (showsSessionOptionAsSwitch(descriptor)) {
             return descriptorRowElements(
               {
                 descriptor,

mobile/src/session/native-chat/input/MobileNativeChatSessionOptionRows.tsx

@@ -17,6 +17,10 @@ import {
   nativeChatSessionOptionActionLabel,
   nativeChatSessionOptionLabel
 } from '../../../../../src/shared/native-chat/input/native-chat-session-option-labels'
+import {
+  loneFastTier,
+  speedButtonTiers
+} from '../../../../../src/shared/native-chat/input/native-chat-session-speed-tiers'
 import { sayMobileNativeChatSessionOption as say } from './native-chat-session-option-copy'
 import { MobileSwitch } from '../../../components/MobileSwitch'
 
@@ -131,6 +135,20 @@ type DescriptorRowsProps = {
   moreChoices?: { shown: boolean; onToggle: () => void }
 }
 
+/** A Fast-only speed, which toggles on one row like Claude's Fast mode. */
+function fastSpeedSwitch(descriptor: SessionOptionDescriptor) {
+  const speed = speedButtonTiers(descriptor)
+  const fast = speed ? loneFastTier(speed.tiers) : undefined
+  return speed && fast ? { standard: speed.standard, fast } : null
+}
+
+export function showsSessionOptionAsSwitch(descriptor: SessionOptionDescriptor): boolean {
+  return (
+    !descriptor.action &&
+    (descriptor.kind.type === 'boolean' || fastSpeedSwitch(descriptor) !== null)
+  )
+}
+
 /** One descriptor's rows as an array, so a ListGroup can draw the separators between them. */
 export function descriptorRowElements(
   {
@@ -156,8 +174,10 @@ export function descriptorRowElements(
     ]
   }
   // An unknown baseline still renders a switch; the source marker prevents implying the value was confirmed.
-  if (descriptor.kind.type === 'boolean') {
-    const label = nativeChatSessionOptionLabel(descriptor, say)
+  const fastSpeed = fastSpeedSwitch(descriptor)
+  if (descriptor.kind.type === 'boolean' || fastSpeed) {
+    const { kind } = descriptor
+    const label = fastSpeed ? say('fastMode') : nativeChatSessionOptionLabel(descriptor, say)
     const marker = sessionOptionValueMarker(descriptor)
     return [
       <ListRow
@@ -173,8 +193,16 @@ export function descriptorRowElements(
         accessory={
           <MobileSwitch
             accessibilityLabel={label}
-            value={descriptor.kind.currentValue}
-            onValueChange={(next) => onSetOption(next)}
+            value={
+              kind.type === 'boolean'
+                ? kind.currentValue
+                : kind.currentValue === fastSpeed?.fast.value
+            }
+            onValueChange={(next) =>
+              onSetOption(
+                fastSpeed ? (next ? fastSpeed.fast.value : fastSpeed.standard.value) : next
+              )
+            }
             disabled={locked}
           />
         }

src/renderer/src/components/native-chat/session/options/controls/NativeChatSessionOptionRows.tsx

@@ -22,7 +22,8 @@ import {
 } from '../../../../../../../shared/native-chat/input/native-chat-session-option-labels'
 import { sayNativeChatSessionOptionTranslated as say } from './native-chat-session-option-labels-text'
 import { NativeChatSessionOptionWriteGroup } from './NativeChatSessionOptionWriteGroup'
-import { NativeChatSessionSpeedButton, speedButtonTiers } from './NativeChatSessionSpeedButton'
+import { NativeChatSessionSpeedButton } from './NativeChatSessionSpeedButton'
+import { speedButtonTiers } from '../../../../../../../shared/native-chat/input/native-chat-session-speed-tiers'
 
 type NativeChatSessionOptionRowsProps = {
   /** The current model's options, in display order. */

src/renderer/src/components/native-chat/session/options/controls/NativeChatSessionSpeedButton.tsx

@@ -8,28 +8,14 @@ import {
   DropdownMenuTrigger
 } from '@/components/ui/dropdown-menu'
 import type {
-  SessionOptionDescriptor,
   SessionOptionSelectChoice,
   SessionOptionValue
 } from '../../../../../../../shared/native-chat/input/native-chat-session-options'
 import { nativeChatSessionChoiceLabel } from '../../../../../../../shared/native-chat/input/native-chat-session-option-labels'
 import { isFastServiceTier } from '../../../../../../../shared/agent-session/options/structured-agent-session-discovered-model'
+import { loneFastTier } from '../../../../../../../shared/native-chat/input/native-chat-session-speed-tiers'
 import { sayNativeChatSessionOptionTranslated as say } from './native-chat-session-option-labels-text'
 
-const STANDARD_TIER = 'default'
-
-/** Standard plus the other tiers, or null when the select is not a speed choice with any. */
-export function speedButtonTiers(
-  descriptor: SessionOptionDescriptor
-): { standard: SessionOptionSelectChoice; tiers: SessionOptionSelectChoice[] } | null {
-  if (descriptor.id !== 'serviceTier' || descriptor.kind.type !== 'select') {
-    return null
-  }
-  const standard = descriptor.kind.choices.find((choice) => choice.value === STANDARD_TIER)
-  const tiers = descriptor.kind.choices.filter((choice) => choice.value !== STANDARD_TIER)
-  return standard && tiers.length > 0 ? { standard, tiers } : null
-}
-
 /** A lone Fast tier toggles like Claude's Fast; anything else opens a list instead of a segmented switcher. */
 export function NativeChatSessionSpeedButton(props: {
   label: string
@@ -46,8 +32,8 @@ export function NativeChatSessionSpeedButton(props: {
   const nameOf = (choice: SessionOptionSelectChoice) =>
     nativeChatSessionChoiceLabel(choice, say, 'serviceTier')
   // Only Fast takes the toggle and bolt; Flex and other tiers are picked from the list.
-  if (tiers.length === 1 && isFastServiceTier(tiers[0])) {
-    const only = tiers[0]
+  const only = loneFastTier(tiers)
+  if (only) {
     return (
       <Toggle
         variant="chip"

src/shared/native-chat/input/native-chat-session-speed-tiers.ts

@@ -0,0 +1,29 @@
+import type {
+  SessionOptionDescriptor,
+  SessionOptionSelectChoice
+} from './native-chat-session-options'
+import { isFastServiceTier } from '../../agent-session/options/structured-agent-session-discovered-model'
+
+const STANDARD_TIER = 'default'
+
+export type SessionSpeedTiers = {
+  standard: SessionOptionSelectChoice
+  tiers: SessionOptionSelectChoice[]
+}
+
+/** Standard plus the other tiers, or null when the select is not a speed choice with any. */
+export function speedButtonTiers(descriptor: SessionOptionDescriptor): SessionSpeedTiers | null {
+  if (descriptor.id !== 'serviceTier' || descriptor.kind.type !== 'select') {
+    return null
+  }
+  const standard = descriptor.kind.choices.find((choice) => choice.value === STANDARD_TIER)
+  const tiers = descriptor.kind.choices.filter((choice) => choice.value !== STANDARD_TIER)
+  return standard && tiers.length > 0 ? { standard, tiers } : null
+}
+
+/** A lone Fast tier toggles like Claude's Fast; Flex and several tiers are picked from a list. */
+export function loneFastTier(
+  tiers: readonly SessionOptionSelectChoice[]
+): SessionOptionSelectChoice | undefined {
+  return tiers.length === 1 && isFastServiceTier(tiers[0]) ? tiers[0] : undefined
+}