diff --git a/packages/ui/src/components/chat/ModelControls.tsx b/packages/ui/src/components/chat/ModelControls.tsx
index 3fbf959b..262664b9 100644
--- a/packages/ui/src/components/chat/ModelControls.tsx
+++ b/packages/ui/src/components/chat/ModelControls.tsx
@@ -40,6 +40,11 @@ import { getCurrentIntlLocale, useI18n } from '@/lib/i18n';
 import { useOpenCodeReadiness } from '@/hooks/useOpenCodeReadiness';
 import { eventMatchesShortcut, getEffectiveShortcutCombo, normalizeCombo } from '@/lib/shortcuts';
 import { markStartupTrace } from '@/lib/startupTrace';
+import {
+    findLatestUserModelChoice,
+    shouldPreserveManualModelOverride,
+} from '@/lib/messages/userModelChoice';
+import { getSyncParts } from '@/sync/sync-refs';
 
 type IconComponent = IconName;
 
@@ -645,37 +650,14 @@ export const ModelControls: React.FC<ModelControlsProps> = ({
         currentSessionDirectory ?? undefined,
     );
     const currentSessionMessagesFromSync = useSessionMessages(currentSessionId ?? '', currentSessionDirectory ?? undefined);
+    // Skip synthetic subagent-completion nudges — restoring from them resets a
+    // manual model override back to the agent default (issue #2404).
     const latestLoadedUserChoice = React.useMemo(() => {
-        for (let i = currentSessionMessagesFromSync.length - 1; i >= 0; i -= 1) {
-            const message = currentSessionMessagesFromSync[i] as typeof currentSessionMessagesFromSync[number] & {
-                model?: { providerID?: string; modelID?: string; variant?: string };
-                variant?: string;
-                mode?: string;
-            };
-            if (message.role !== 'user') {
-                continue;
-            }
-
-            const providerID = typeof message.model?.providerID === 'string' && message.model.providerID.trim().length > 0
-                ? message.model.providerID
-                : undefined;
-            const modelID = typeof message.model?.modelID === 'string' && message.model.modelID.trim().length > 0
-                ? message.model.modelID
-                : undefined;
-            const agent = typeof message.agent === 'string' && message.agent.trim().length > 0
-                ? message.agent
-                : (typeof message.mode === 'string' && message.mode.trim().length > 0 ? message.mode : undefined);
-            // OpenCode 1.4.0 moved variant from top-level to model.variant.
-            // Prefer the new location, fall back to the legacy one for older servers.
-            const variantCandidate = message.model?.variant ?? message.variant;
-            const variant = typeof variantCandidate === 'string' && variantCandidate.trim().length > 0
-                ? variantCandidate
-                : undefined;
-
-            return { id: message.id, agent, providerID, modelID, variant };
-        }
-        return null;
-    }, [currentSessionMessagesFromSync]);
+        return findLatestUserModelChoice(
+            currentSessionMessagesFromSync,
+            (messageId) => getSyncParts(messageId, currentSessionDirectory ?? undefined),
+        );
+    }, [currentSessionDirectory, currentSessionMessagesFromSync]);
 
     const tryApplyModelSelection = React.useCallback(
         (providerId: string, modelId: string, agentName?: string): ModelApplyResult => {
@@ -828,6 +810,25 @@ export const ModelControls: React.FC<ModelControlsProps> = ({
             return;
         }
 
+        // Manual session override wins over historical / synthetic message metadata.
+        const savedSessionModel = getSessionModelSelection(currentSessionId);
+        if (shouldPreserveManualModelOverride({
+            selectionSource: useConfigStore.getState().selectionSource,
+            savedSessionModel,
+            candidate: latestLoadedUserChoice,
+        })) {
+            if (savedSessionModel) {
+                applyModelSelectionWithVariant(
+                    savedSessionModel.providerId,
+                    savedSessionModel.modelId,
+                    resolveModelVariantSelection(savedSessionModel.providerId, savedSessionModel.modelId),
+                    currentAgentName || undefined,
+                );
+            }
+            latestLoadedUserChoiceRestoreRef.current = restoreKey;
+            return;
+        }
+
         if (latestLoadedUserChoice.agent && currentAgentName !== latestLoadedUserChoice.agent) {
             setAgent(latestLoadedUserChoice.agent);
         }
@@ -869,6 +870,8 @@ export const ModelControls: React.FC<ModelControlsProps> = ({
         setAgent,
         applyModelSelectionWithVariant,
         getModelVariantOptions,
+        getSessionModelSelection,
+        resolveModelVariantSelection,
         saveSessionAgentSelection,
         saveAgentModelVariantForSession,
         saveSessionModelSelection,
diff --git a/packages/ui/src/lib/messages/userModelChoice.test.ts b/packages/ui/src/lib/messages/userModelChoice.test.ts
new file mode 100644
index 00000000..e0c43ef9
--- /dev/null
+++ b/packages/ui/src/lib/messages/userModelChoice.test.ts
@@ -0,0 +1,145 @@
+import { describe, expect, test } from 'bun:test'
+import type { Message, Part } from '@opencode-ai/sdk/v2'
+
+import {
+  extractUserModelChoice,
+  findLatestUserModelChoice,
+  shouldPreserveManualModelOverride,
+} from './userModelChoice'
+
+const userMessage = (
+  id: string,
+  model: { providerID: string; modelID: string },
+  agent = 'custom-agent',
+): Message => ({
+  id,
+  sessionID: 'ses_1',
+  role: 'user',
+  time: { created: 1 },
+  agent,
+  model,
+} as Message)
+
+const assistantMessage = (id: string): Message => ({
+  id,
+  sessionID: 'ses_1',
+  role: 'assistant',
+  time: { created: 2 },
+  parentID: 'u1',
+  modelID: 'model-a',
+  providerID: 'provider',
+} as Message)
+
+const textPart = (id: string, text: string, synthetic = false): Part => ({
+  id,
+  sessionID: 'ses_1',
+  messageID: 'u1',
+  type: 'text',
+  text,
+  ...(synthetic ? { synthetic: true } : {}),
+} as Part)
+
+describe('findLatestUserModelChoice', () => {
+  test('returns the latest real user prompt model', () => {
+    const messages = [
+      userMessage('u1', { providerID: 'provider', modelID: 'model-a' }),
+      assistantMessage('a1'),
+      userMessage('u2', { providerID: 'provider', modelID: 'model-b' }),
+    ]
+    const partsById: Record<string, Part[]> = {
+      u1: [textPart('p1', 'first')],
+      u2: [textPart('p2', 'second')],
+    }
+
+    const choice = findLatestUserModelChoice(messages, (id) => partsById[id])
+    expect(choice?.id).toBe('u2')
+    expect(choice?.modelID).toBe('model-b')
+    expect(choice?.providerID).toBe('provider')
+    expect(choice?.agent).toBe('custom-agent')
+  })
+
+  test('[issue-2404] skips synthetic subagent-completion nudges so manual override is not clobbered', () => {
+    // Real prompt sent with the manual override (model-b).
+    const realPrompt = userMessage('u-real', { providerID: 'provider', modelID: 'model-b' })
+    // After a delegated child session goes idle, OpenCode injects a synthetic
+    // user nudge that often carries the agent default model (model-a).
+    const syntheticNudge = userMessage('u-nudge', { providerID: 'provider', modelID: 'model-a' })
+    const messages = [realPrompt, assistantMessage('a1'), syntheticNudge]
+    const partsById: Record<string, Part[]> = {
+      'u-real': [textPart('p-real', 'please investigate', false)],
+      'u-nudge': [textPart('p-nudge', 'Subagent finished.', true)],
+    }
+
+    const choice = findLatestUserModelChoice(messages, (id) => partsById[id])
+    expect(choice?.id).toBe('u-real')
+    expect(choice?.modelID).toBe('model-b')
+  })
+
+  test('skips user messages whose parts have not loaded yet', () => {
+    const messages = [
+      userMessage('u1', { providerID: 'provider', modelID: 'model-a' }),
+      userMessage('u2', { providerID: 'provider', modelID: 'model-b' }),
+    ]
+    const partsById: Record<string, Part[]> = {
+      u1: [textPart('p1', 'first')],
+      // u2 parts missing
+    }
+
+    const choice = findLatestUserModelChoice(messages, (id) => partsById[id])
+    expect(choice?.id).toBe('u1')
+    expect(choice?.modelID).toBe('model-a')
+  })
+
+  test('returns null when only synthetic user messages exist', () => {
+    const messages = [userMessage('u-nudge', { providerID: 'provider', modelID: 'model-a' })]
+    const partsById: Record<string, Part[]> = {
+      'u-nudge': [textPart('p-nudge', 'Subagent finished.', true)],
+    }
+
+    expect(findLatestUserModelChoice(messages, (id) => partsById[id])).toBeNull()
+  })
+})
+
+describe('shouldPreserveManualModelOverride', () => {
+  test('preserves manual override when it differs from the candidate message model', () => {
+    expect(shouldPreserveManualModelOverride({
+      selectionSource: 'manual',
+      savedSessionModel: { providerId: 'provider', modelId: 'model-b' },
+      candidate: { providerID: 'provider', modelID: 'model-a' },
+    })).toBe(true)
+  })
+
+  test('does not preserve when selection matches the candidate', () => {
+    expect(shouldPreserveManualModelOverride({
+      selectionSource: 'manual',
+      savedSessionModel: { providerId: 'provider', modelId: 'model-b' },
+      candidate: { providerID: 'provider', modelID: 'model-b' },
+    })).toBe(false)
+  })
+
+  test('does not preserve auto selections', () => {
+    expect(shouldPreserveManualModelOverride({
+      selectionSource: 'auto',
+      savedSessionModel: { providerId: 'provider', modelId: 'model-b' },
+      candidate: { providerID: 'provider', modelID: 'model-a' },
+    })).toBe(false)
+  })
+
+  test('preserves manual override when candidate has no model', () => {
+    expect(shouldPreserveManualModelOverride({
+      selectionSource: 'manual',
+      savedSessionModel: { providerId: 'provider', modelId: 'model-b' },
+      candidate: { providerID: undefined, modelID: undefined },
+    })).toBe(true)
+  })
+})
+
+describe('extractUserModelChoice', () => {
+  test('reads variant from model.variant', () => {
+    const message = {
+      ...userMessage('u1', { providerID: 'provider', modelID: 'model-b' }),
+      model: { providerID: 'provider', modelID: 'model-b', variant: 'high' },
+    } as Message
+    expect(extractUserModelChoice(message as never)?.variant).toBe('high')
+  })
+})
diff --git a/packages/ui/src/lib/messages/userModelChoice.ts b/packages/ui/src/lib/messages/userModelChoice.ts
new file mode 100644
index 00000000..a94bfbfc
--- /dev/null
+++ b/packages/ui/src/lib/messages/userModelChoice.ts
@@ -0,0 +1,103 @@
+import type { Message, Part } from '@opencode-ai/sdk/v2'
+
+import { isFullySyntheticMessage } from './synthetic'
+
+type UserModelChoice = {
+  id: string
+  agent?: string
+  providerID?: string
+  modelID?: string
+  variant?: string
+}
+
+type MessageLike = Message & {
+  model?: { providerID?: string; modelID?: string; variant?: string }
+  variant?: string
+  mode?: string
+}
+
+/**
+ * Extract agent/model selection metadata from a user message, if present.
+ */
+export const extractUserModelChoice = (message: MessageLike): UserModelChoice | null => {
+  if (message.role !== 'user') {
+    return null
+  }
+
+  const providerID = typeof message.model?.providerID === 'string' && message.model.providerID.trim().length > 0
+    ? message.model.providerID
+    : undefined
+  const modelID = typeof message.model?.modelID === 'string' && message.model.modelID.trim().length > 0
+    ? message.model.modelID
+    : undefined
+  const agent = typeof message.agent === 'string' && message.agent.trim().length > 0
+    ? message.agent
+    : (typeof message.mode === 'string' && message.mode.trim().length > 0 ? message.mode : undefined)
+  // OpenCode 1.4.0 moved variant from top-level to model.variant.
+  const variantCandidate = message.model?.variant ?? message.variant
+  const variant = typeof variantCandidate === 'string' && variantCandidate.trim().length > 0
+    ? variantCandidate
+    : undefined
+
+  return { id: message.id, agent, providerID, modelID, variant }
+}
+
+/**
+ * Find the latest *real* user prompt's model/agent choice.
+ *
+ * Synthetic user messages (e.g. subagent-completion nudges injected when a
+ * delegated child session goes idle) must not drive the composer model
+ * selector — restoring from them clobber a manual session override and reset
+ * to the agent default.
+ *
+ * Messages whose parts have not been loaded yet are skipped so an incomplete
+ * snapshot cannot be treated as authoritative.
+ */
+export const findLatestUserModelChoice = (
+  messages: readonly MessageLike[],
+  getParts: (messageId: string) => Part[] | undefined,
+): UserModelChoice | null => {
+  for (let i = messages.length - 1; i >= 0; i -= 1) {
+    const message = messages[i]
+    if (message.role !== 'user') {
+      continue
+    }
+
+    const parts = getParts(message.id)
+    if (!Array.isArray(parts) || parts.length === 0) {
+      continue
+    }
+    if (isFullySyntheticMessage(parts)) {
+      continue
+    }
+
+    return extractUserModelChoice(message)
+  }
+
+  return null
+}
+
+/**
+ * When the user has a manual session model override, historical (or synthetic)
+ * user-message metadata must not overwrite it. After a real send the selection
+ * store is updated to match the message, so a conflict means the picker was
+ * changed after the last prompt — keep the override.
+ */
+export const shouldPreserveManualModelOverride = ({
+  selectionSource,
+  savedSessionModel,
+  candidate,
+}: {
+  selectionSource: 'auto' | 'manual' | undefined
+  savedSessionModel: { providerId: string; modelId: string } | null | undefined
+  candidate: Pick<UserModelChoice, 'providerID' | 'modelID'> | null | undefined
+}): boolean => {
+  if (selectionSource !== 'manual' || !savedSessionModel?.providerId || !savedSessionModel.modelId) {
+    return false
+  }
+  if (!candidate?.providerID || !candidate.modelID) {
+    return true
+  }
+  return savedSessionModel.providerId !== candidate.providerID
+    || savedSessionModel.modelId !== candidate.modelID
+}
diff --git a/packages/ui/src/stores/useConfigStore.test.ts b/packages/ui/src/stores/useConfigStore.test.ts
index 0b2b18c6..52dbe3e6 100644
--- a/packages/ui/src/stores/useConfigStore.test.ts
+++ b/packages/ui/src/stores/useConfigStore.test.ts
@@ -522,6 +522,73 @@ describe('useConfigStore provider persistence', () => {
     expect(state.currentVariant).toBe('high');
   });
 
+  test('[issue-2404] setAgent keeps session model override over agent default model', () => {
+    // Custom agent default is model-a; user manually overrode to model-b for this session.
+    // Re-applying setAgent (e.g. after delegated subtask completion rematerializes the
+    // parent) must keep model-b rather than resetting to the agent pin.
+    const sessionId = 'ses_2404_model_override';
+    const multiModelProvider = {
+      ...provider('provider', 'model-a'),
+      models: [
+        provider('provider', 'model-a').models[0],
+        provider('provider', 'model-b').models[0],
+      ],
+    };
+    useSessionUIStore.setState({ currentSessionId: sessionId });
+    useSelectionStore.getState().saveSessionModelSelection(sessionId, 'provider', 'model-b');
+    useSelectionStore.getState().saveAgentModelForSession(sessionId, 'custom-agent', 'provider', 'model-b');
+    useConfigStore.setState({
+      activeDirectoryKey: DIRECTORY,
+      providers: [multiModelProvider],
+      agents: [testAgent('custom-agent', { model: { providerID: 'provider', modelID: 'model-a' } })],
+      currentProviderId: 'provider',
+      currentModelId: 'model-b',
+      currentAgentName: 'custom-agent',
+      selectionSource: 'manual',
+      currentVariant: undefined,
+      directoryScoped: {},
+    });
+
+    useConfigStore.getState().setAgent('custom-agent');
+
+    const state = useConfigStore.getState();
+    expect(state.currentProviderId).toBe('provider');
+    expect(state.currentModelId).toBe('model-b');
+    expect(useSelectionStore.getState().getAgentModelForSession(sessionId, 'custom-agent')).toEqual({
+      providerId: 'provider',
+      modelId: 'model-b',
+    });
+  });
+
+  test('[issue-2404] setAgent uses agent default when no session override exists', () => {
+    const sessionId = 'ses_2404_agent_default';
+    const multiModelProvider = {
+      ...provider('provider', 'model-a'),
+      models: [
+        provider('provider', 'model-a').models[0],
+        provider('provider', 'model-b').models[0],
+      ],
+    };
+    useSessionUIStore.setState({ currentSessionId: sessionId });
+    useConfigStore.setState({
+      activeDirectoryKey: DIRECTORY,
+      providers: [multiModelProvider],
+      agents: [testAgent('custom-agent', { model: { providerID: 'provider', modelID: 'model-a' } })],
+      currentProviderId: 'provider',
+      currentModelId: 'model-b',
+      currentAgentName: undefined,
+      selectionSource: 'auto',
+      currentVariant: undefined,
+      directoryScoped: {},
+    });
+
+    useConfigStore.getState().setAgent('custom-agent');
+
+    const state = useConfigStore.getState();
+    expect(state.currentProviderId).toBe('provider');
+    expect(state.currentModelId).toBe('model-a');
+  });
+
   test('loadAgents does not fetch OpenCode config directly', async () => {
     useConfigStore.setState({
       activeDirectoryKey: DIRECTORY,
diff --git a/packages/ui/src/stores/useConfigStore.ts b/packages/ui/src/stores/useConfigStore.ts
index 4fe82ee2..4a7dfd2e 100644
--- a/packages/ui/src/stores/useConfigStore.ts
+++ b/packages/ui/src/stores/useConfigStore.ts
@@ -2503,20 +2503,13 @@ export const useConfigStore = create<ConfigStore>()(
                             return undefined;
                         };
 
-                        // Prefer the selected agent's configured model when switching agents.
                         const agent = agents.find((candidate) => candidate.name === agentName);
-                        const agentModelSelection = agent?.model;
-                        if (agentModelSelection?.providerID && agentModelSelection?.modelID) {
-                            const { providerID, modelID } = agentModelSelection;
-                            const agentProvider = providers.find((provider) => provider.id === providerID);
-                            const agentModel = agentProvider?.models.find((model) => model.id === modelID);
-
-                            if (agentModel) {
-                                applyResolvedModelSelection(providerID, modelID, resolveVariantForModel(providerID, modelID, agent?.variant));
-                                return;
-                            }
-                        }
 
+                        // Prefer a session-level manual override for this agent over the
+                        // agent's configured default. Re-applying setAgent after subtask
+                        // completion / rematerialization must not clobber the override
+                        // (issue #2404). Explicit agent-picker switches still force the
+                        // agent default via ModelControls' shouldPreferAgentModel path.
                         if (currentSessionId) {
                             const existingAgentModel = useSelectionStore.getState().getAgentModelForSession(currentSessionId, agentName);
                             if (existingAgentModel && hasProviderModel(providers, existingAgentModel.providerId, existingAgentModel.modelId)) {
@@ -2532,6 +2525,19 @@ export const useConfigStore = create<ConfigStore>()(
                             }
                         }
 
+                        // No session override — use the agent's configured/pinned model.
+                        const agentModelSelection = agent?.model;
+                        if (agentModelSelection?.providerID && agentModelSelection?.modelID) {
+                            const { providerID, modelID } = agentModelSelection;
+                            const agentProvider = providers.find((provider) => provider.id === providerID);
+                            const agentModel = agentProvider?.models.find((model) => model.id === modelID);
+
+                            if (agentModel) {
+                                applyResolvedModelSelection(providerID, modelID, resolveVariantForModel(providerID, modelID, agent?.variant));
+                                return;
+                            }
+                        }
+
                         // If the agent has no preferred model, use settings default.
                         if (settingsDefaultModel) {
                             const parsed = parseModelString(settingsDefaultModel);
diff --git a/packages/ui/src/sync/__tests__/issue-2404.test.ts b/packages/ui/src/sync/__tests__/issue-2404.test.ts
new file mode 100644
index 00000000..16bf87a5
--- /dev/null
+++ b/packages/ui/src/sync/__tests__/issue-2404.test.ts
@@ -0,0 +1,200 @@
+import { beforeEach, describe, expect, test } from 'bun:test'
+import type { Message, Part } from '@opencode-ai/sdk/v2'
+
+import {
+  findLatestUserModelChoice,
+  shouldPreserveManualModelOverride,
+} from '@/lib/messages/userModelChoice'
+
+/**
+ * Regression for openchamber/openchamber#2404:
+ * custom agent default model A → manual override to B → delegate subtask →
+ * after child completes, synthetic completion nudge must not revert to A.
+ */
+describe('issue #2404 model override persistence across delegated subtask', () => {
+  const sessionId = 'ses_2404'
+  const agentName = 'custom-agent'
+  const agentDefault = { providerID: 'provider', modelID: 'model-a' }
+  const manualOverride = { providerID: 'provider', modelID: 'model-b' }
+
+  let sessionModelSelections: Map<string, { providerId: string; modelId: string }>
+  let sessionAgentModelSelections: Map<string, Map<string, { providerId: string; modelId: string }>>
+  let selectionSource: 'auto' | 'manual'
+  let currentProviderId: string
+  let currentModelId: string
+
+  beforeEach(() => {
+    sessionModelSelections = new Map()
+    sessionAgentModelSelections = new Map()
+    selectionSource = 'auto'
+    currentProviderId = agentDefault.providerID
+    currentModelId = agentDefault.modelID
+  })
+
+  const createSessionWithAgentDefault = () => {
+    // Session starts on the custom agent's pinned model A.
+    currentProviderId = agentDefault.providerID
+    currentModelId = agentDefault.modelID
+    selectionSource = 'auto'
+    sessionModelSelections.set(sessionId, {
+      providerId: agentDefault.providerID,
+      modelId: agentDefault.modelID,
+    })
+    sessionAgentModelSelections.set(sessionId, new Map([
+      [agentName, { providerId: agentDefault.providerID, modelId: agentDefault.modelID }],
+    ]))
+  }
+
+  const setManualModelOverride = () => {
+    selectionSource = 'manual'
+    currentProviderId = manualOverride.providerID
+    currentModelId = manualOverride.modelID
+    sessionModelSelections.set(sessionId, {
+      providerId: manualOverride.providerID,
+      modelId: manualOverride.modelID,
+    })
+    const agentMap = sessionAgentModelSelections.get(sessionId) ?? new Map()
+    agentMap.set(agentName, {
+      providerId: manualOverride.providerID,
+      modelId: manualOverride.modelID,
+    })
+    sessionAgentModelSelections.set(sessionId, agentMap)
+  }
+
+  const completeDelegatedSubtask = () => {
+    // Parent already has the real user prompt (sent with override B) plus a
+    // synthetic subagent-completion nudge that carries the agent default A.
+    const messages: Message[] = [
+      {
+        id: 'u-real',
+        sessionID: sessionId,
+        role: 'user',
+        time: { created: 1 },
+        agent: agentName,
+        model: manualOverride,
+      } as Message,
+      {
+        id: 'a1',
+        sessionID: sessionId,
+        role: 'assistant',
+        time: { created: 2 },
+        parentID: 'u-real',
+        providerID: manualOverride.providerID,
+        modelID: manualOverride.modelID,
+      } as Message,
+      {
+        id: 'u-nudge',
+        sessionID: sessionId,
+        role: 'user',
+        time: { created: 3 },
+        agent: agentName,
+        model: agentDefault,
+      } as Message,
+    ]
+    const partsById: Record<string, Part[]> = {
+      'u-real': [{
+        id: 'p-real',
+        sessionID: sessionId,
+        messageID: 'u-real',
+        type: 'text',
+        text: 'Delegate a subtask',
+      } as Part],
+      'u-nudge': [{
+        id: 'p-nudge',
+        sessionID: sessionId,
+        messageID: 'u-nudge',
+        type: 'text',
+        text: 'Subagent finished.',
+        synthetic: true,
+      } as Part],
+    }
+
+    const latestChoice = findLatestUserModelChoice(messages, (id) => partsById[id])
+    const saved = sessionModelSelections.get(sessionId) ?? null
+
+    // Composer restore must ignore the synthetic nudge and keep the override.
+    expect(latestChoice?.modelID).toBe(manualOverride.modelID)
+    expect(shouldPreserveManualModelOverride({
+      selectionSource,
+      savedSessionModel: saved,
+      candidate: {
+        providerID: agentDefault.providerID,
+        modelID: agentDefault.modelID,
+      },
+    })).toBe(true)
+
+    // Re-applying the session agent (as ModelControls may after rematerialization)
+    // must also prefer the stored override over the agent pin.
+    const agentOverride = sessionAgentModelSelections.get(sessionId)?.get(agentName)
+    if (agentOverride) {
+      currentProviderId = agentOverride.providerId
+      currentModelId = agentOverride.modelId
+    } else {
+      currentProviderId = agentDefault.providerID
+      currentModelId = agentDefault.modelID
+    }
+  }
+
+  test('manual override survives delegated subtask completion', () => {
+    createSessionWithAgentDefault()
+    setManualModelOverride()
+    completeDelegatedSubtask()
+
+    expect(selectionSource).toBe('manual')
+    expect(currentProviderId).toBe(manualOverride.providerID)
+    expect(currentModelId).toBe(manualOverride.modelID)
+    expect(sessionModelSelections.get(sessionId)).toEqual({
+      providerId: manualOverride.providerID,
+      modelId: manualOverride.modelID,
+    })
+  })
+
+  test('agent default is used when no manual override was set', () => {
+    createSessionWithAgentDefault()
+    // No setManualModelOverride — stay on agent default through subtask completion.
+    const messages: Message[] = [
+      {
+        id: 'u-real',
+        sessionID: sessionId,
+        role: 'user',
+        time: { created: 1 },
+        agent: agentName,
+        model: agentDefault,
+      } as Message,
+      {
+        id: 'u-nudge',
+        sessionID: sessionId,
+        role: 'user',
+        time: { created: 2 },
+        agent: agentName,
+        model: agentDefault,
+      } as Message,
+    ]
+    const partsById: Record<string, Part[]> = {
+      'u-real': [{
+        id: 'p-real',
+        sessionID: sessionId,
+        messageID: 'u-real',
+        type: 'text',
+        text: 'Delegate a subtask',
+      } as Part],
+      'u-nudge': [{
+        id: 'p-nudge',
+        sessionID: sessionId,
+        messageID: 'u-nudge',
+        type: 'text',
+        text: 'Subagent finished.',
+        synthetic: true,
+      } as Part],
+    }
+
+    const latestChoice = findLatestUserModelChoice(messages, (id) => partsById[id])
+    expect(latestChoice?.modelID).toBe(agentDefault.modelID)
+    expect(shouldPreserveManualModelOverride({
+      selectionSource: 'auto',
+      savedSessionModel: sessionModelSelections.get(sessionId),
+      candidate: latestChoice,
+    })).toBe(false)
+    expect(currentModelId).toBe(agentDefault.modelID)
+  })
+})
diff --git a/packages/ui/src/sync/session-ui-store.ts b/packages/ui/src/sync/session-ui-store.ts
index 895f5062..4ecdb87d 100644
--- a/packages/ui/src/sync/session-ui-store.ts
+++ b/packages/ui/src/sync/session-ui-store.ts
@@ -30,6 +30,7 @@ import { markPendingUserSendAnimation } from "@/lib/userSendAnimation"
 import { normalizePath } from "@/lib/pathNormalization"
 import { flattenAssistantTextParts } from "@/lib/messages/messageText"
 import { composeForkSessionMessage } from "@/lib/messages/executionMeta"
+import { findLatestUserModelChoice } from "@/lib/messages/userModelChoice"
 import { waitForPendingDraftWorktreeRequest } from "@/lib/worktrees/pendingDraftWorktree"
 import { waitForWorktreeBootstrap } from "@/lib/worktrees/worktreeBootstrap"
 import { getWorktreeSetupWaitEnabled } from "@/lib/openchamberConfig"
@@ -1713,33 +1714,19 @@ export const useSessionUIStore = create<SessionUIState>()((set, get) => ({
   getLastUserChoice: (sessionId) => {
     const directory = get().getDirectoryForSession(sessionId) ?? undefined
     const messages = getSyncMessages(sessionId, directory)
-    for (let i = messages.length - 1; i >= 0; i -= 1) {
-      const message = messages[i] as Message & {
-        model?: { providerID?: string; modelID?: string; variant?: string }
-        variant?: string
-        mode?: string
-      }
-      if (message.role !== "user") {
-        continue
-      }
-
-      const providerID = typeof message.model?.providerID === "string" && message.model.providerID.trim().length > 0
-        ? message.model.providerID
-        : undefined
-      const modelID = typeof message.model?.modelID === "string" && message.model.modelID.trim().length > 0
-        ? message.model.modelID
-        : undefined
-      const agent = typeof message.agent === "string" && message.agent.trim().length > 0
-        ? message.agent
-        : (typeof message.mode === "string" && message.mode.trim().length > 0 ? message.mode : undefined)
-      const variantCandidate = message.model?.variant ?? message.variant
-      const variant = typeof variantCandidate === "string" && variantCandidate.trim().length > 0
-        ? variantCandidate
-        : undefined
-
-      return { agent, providerID, modelID, variant }
+    const choice = findLatestUserModelChoice(
+      messages,
+      (messageId) => getSyncParts(messageId, directory),
+    )
+    if (!choice) {
+      return null
+    }
+    return {
+      agent: choice.agent,
+      providerID: choice.providerID,
+      modelID: choice.modelID,
+      variant: choice.variant,
     }
-    return null
   },
 
   getCurrentAgent: (sessionId) => {