Keep composer mode preferences stable (#1658)

* fix(app): preserve composer mode preferences

Treat undefined provider preference updates as no-ops, and keep saved mode selections instead of silently defaulting them when provider metadata is incomplete or does not list the saved mode.

* fix(app): document mode preference preservation

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 ?? "";
 }
 
+const normalizeSelectedModeId = normalizeSelectedModelId;
+
+function resolvePreferredModeId(input: {
+  initialModeId?: string | null;
+  preferredModeId?: string | null;
+  providerDef: AgentProviderDefinition | undefined;
+}): string {
+  // Saved modes are user intent. Provider create config validates unknown modes
+  // at submission time, so background form resolution should not erase them.
+  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,