Keep composer mode preferences stable

packages/app/src/create-agent-preferences/preferences.test.ts

@@ -81,6 +81,39 @@ describe("create agent preferences", () => {
     });
   });
 
+  it("does not erase a saved mode when a later partial update has no mode", () => {
+    expect(
+      mergeProviderPreferences({
+        preferences: {
+          provider: "codex",
+          providerPreferences: {
+            codex: {
+              model: "gpt-5.5",
+              mode: "full-access",
+              thinkingByModel: { "gpt-5.5": "high" },
+            },
+          },
+        },
+        provider: "codex",
+        updates: {
+          model: "gpt-5.6",
+          mode: undefined,
+          thinkingByModel: undefined,
+          featureValues: undefined,
+        },
+      }),
+    ).toEqual({
+      provider: "codex",
+      providerPreferences: {
+        codex: {
+          model: "gpt-5.6",
+          mode: "full-access",
+          thinkingByModel: { "gpt-5.5": "high" },
+        },
+      },
+    });
+  });
+
   it("loads invalid stored preferences as empty preferences", () => {
     expect(parseFormPreferences({ providerPreferences: { codex: { mode: 42 } } })).toEqual({});
   });

packages/app/src/create-agent-preferences/preferences.ts

@@ -46,6 +46,43 @@ export function parseFormPreferences(value: unknown): FormPreferences {
   return result.success ? result.data : DEFAULT_FORM_PREFERENCES;
 }
 
+function mergeDefinedRecord<T>(
+  existing: Record<string, T> | undefined,
+  updates: Record<string, T> | undefined,
+): Record<string, T> | undefined {
+  if (updates === undefined) {
+    return existing;
+  }
+  return {
+    ...existing,
+    ...updates,
+  };
+}
+
+function applyProviderPreferenceUpdates(
+  existing: ProviderPreferences,
+  updates: Partial<ProviderPreferences>,
+): ProviderPreferences {
+  const next: ProviderPreferences = { ...existing };
+  const nextThinkingByModel = mergeDefinedRecord(existing.thinkingByModel, updates.thinkingByModel);
+  const nextFeatureValues = mergeDefinedRecord(existing.featureValues, updates.featureValues);
+
+  if (updates.model !== undefined) {
+    next.model = updates.model;
+  }
+  if (updates.mode !== undefined) {
+    next.mode = updates.mode;
+  }
+  if (nextThinkingByModel !== undefined) {
+    next.thinkingByModel = nextThinkingByModel;
+  }
+  if (nextFeatureValues !== undefined) {
+    next.featureValues = nextFeatureValues;
+  }
+
+  return next;
+}
+
 export function mergeProviderPreferences(args: {
   preferences: FormPreferences;
   provider: AgentProvider;
@@ -54,32 +91,13 @@ export function mergeProviderPreferences(args: {
   const { preferences, provider, updates } = args;
   const existingProviderPreferences = preferences.providerPreferences ?? {};
   const existing = existingProviderPreferences[provider] ?? {};
-  const nextThinkingByModel =
-    updates.thinkingByModel === undefined
-      ? existing.thinkingByModel
-      : {
-          ...existing.thinkingByModel,
-          ...updates.thinkingByModel,
-        };
-  const nextFeatureValues =
-    updates.featureValues === undefined
-      ? existing.featureValues
-      : {
-          ...existing.featureValues,
-          ...updates.featureValues,
-        };
 
   return {
     ...preferences,
     provider,
     providerPreferences: {
       ...existingProviderPreferences,
-      [provider]: {
-        ...existing,
-        ...updates,
-        ...(nextThinkingByModel ? { thinkingByModel: nextThinkingByModel } : {}),
-        ...(nextFeatureValues ? { featureValues: nextFeatureValues } : {}),
-      },
+      [provider]: applyProviderPreferenceUpdates(existing, updates),
     },
   };
 }

packages/app/src/provider-selection/resolve-agent-form.test.ts

@@ -511,6 +511,59 @@ describe("resolveFormState", () => {
     expect(resolved.thinkingOptionId).toBe("xhigh");
   });
 
+  it("preserves the saved mode while provider modes are absent from a loading snapshot", () => {
+    const loadingEntries: ProviderSnapshotEntry[] = [
+      {
+        provider: "codex",
+        status: "loading",
+        enabled: true,
+        label: TEST_CODEX_DEFINITION.label,
+        description: TEST_CODEX_DEFINITION.description,
+        defaultModeId: TEST_CODEX_DEFINITION.defaultModeId,
+      },
+    ];
+    const providerDefinitions = buildProviderDefinitions(loadingEntries);
+    const resolvableProviderMap = buildProviderDefinitionMapForStatuses({
+      snapshotEntries: loadingEntries,
+      providerDefinitions,
+      statuses: new Set<ProviderSnapshotEntry["status"]>(["ready", "loading"]),
+    });
+
+    const resolved = resolveFormState(
+      undefined,
+      {
+        provider: "codex",
+        providerPreferences: { codex: { mode: "full-access", model: "gpt-5.3-codex" } },
+      },
+      null,
+      INITIAL_USER_MODIFIED,
+      makeState({ provider: "codex", modeId: "full-access", model: "gpt-5.3-codex" }).form,
+
+      resolvableProviderMap,
+    );
+
+    expect(resolved.provider).toBe("codex");
+    expect(resolved.modeId).toBe("full-access");
+  });
+
+  it("preserves a saved mode that is not in the current mode list", () => {
+    const resolved = resolveFormState(
+      undefined,
+      {
+        provider: "codex",
+        providerPreferences: { codex: { mode: "workspace-write", model: "gpt-5.3-codex" } },
+      },
+      CODEX_MODELS,
+      INITIAL_USER_MODIFIED,
+      makeState({ provider: "codex" }).form,
+
+      codexProviderMap,
+    );
+
+    expect(resolved.provider).toBe("codex");
+    expect(resolved.modeId).toBe("workspace-write");
+  });
+
   it("ignores disabled ready providers when resolving selectable defaults", () => {
     const entries: ProviderSnapshotEntry[] = [
       {

packages/app/src/provider-selection/resolve-agent-form.ts

@@ -144,6 +144,24 @@ export function resolveThinkingOptionId(args: {
   return effectiveModel?.defaultThinkingOptionId ?? thinkingOptions[0]?.id ?? "";
 }
 
+function normalizeSelectedModeId(modeId: string | null | undefined): string {
+  return typeof modeId === "string" ? modeId.trim() : "";
+}
+
+function resolvePreferredModeId(input: {
+  initialModeId?: string | null;
+  preferredModeId?: string | null;
+  providerDef: AgentProviderDefinition | undefined;
+}): string {
+  const initialModeId = normalizeSelectedModeId(input.initialModeId);
+  if (initialModeId) return initialModeId;
+
+  const preferredModeId = normalizeSelectedModeId(input.preferredModeId);
+  if (preferredModeId) return preferredModeId;
+
+  return input.providerDef?.defaultModeId ?? input.providerDef?.modes[0]?.id ?? "";
+}
+
 export function mergeSelectedComposerPreferences(args: {
   preferences: FormPreferences;
   provider: AgentProvider;
@@ -259,18 +277,11 @@ function resolveModeId(input: {
     input;
   if (userModified) return currentModeId;
   if (!provider) return "";
-  const validModeIds = providerDef?.modes.map((m) => m.id) ?? [];
-  if (
-    typeof initialValues?.modeId === "string" &&
-    initialValues.modeId.length > 0 &&
-    validModeIds.includes(initialValues.modeId)
-  ) {
-    return initialValues.modeId;
-  }
-  if (providerPrefs?.mode && validModeIds.includes(providerPrefs.mode)) {
-    return providerPrefs.mode;
-  }
-  return providerDef?.defaultModeId ?? validModeIds[0] ?? "";
+  return resolvePreferredModeId({
+    initialModeId: initialValues?.modeId,
+    preferredModeId: providerPrefs?.mode,
+    providerDef,
+  });
 }
 
 function resolveModelField(input: {
@@ -411,11 +422,10 @@ function pickNextModeForProvider(input: {
   providerPrefs: ProviderPrefs | undefined;
 }): string {
   const { providerDef, providerPrefs } = input;
-  const validModeIds = providerDef?.modes.map((m) => m.id) ?? [];
-  if (providerPrefs?.mode && validModeIds.includes(providerPrefs.mode)) {
-    return providerPrefs.mode;
-  }
-  return providerDef?.defaultModeId ?? "";
+  return resolvePreferredModeId({
+    preferredModeId: providerPrefs?.mode,
+    providerDef,
+  });
 }
 
 function pickNextModeForProviderAndModel(input: {
@@ -425,14 +435,8 @@ function pickNextModeForProviderAndModel(input: {
   providerDef: AgentProviderDefinition | undefined;
   providerPrefs: ProviderPrefs | undefined;
 }): string {
-  const validModeIds = input.providerDef?.modes.map((m) => m.id) ?? [];
-  if (
-    input.currentProvider === input.provider &&
-    input.currentModeId &&
-    validModeIds.includes(input.currentModeId)
-  ) {
-    return input.currentModeId;
-  }
+  const currentModeId = normalizeSelectedModeId(input.currentModeId);
+  if (input.currentProvider === input.provider && currentModeId) return currentModeId;
   return pickNextModeForProvider({
     providerDef: input.providerDef,
     providerPrefs: input.providerPrefs,