diff --git a/packages/app/src/provider-selection/resolve-agent-form.test.ts b/packages/app/src/provider-selection/resolve-agent-form.test.ts
index aa6ca01048..bb7ab5b954 100644
--- a/packages/app/src/provider-selection/resolve-agent-form.test.ts
+++ b/packages/app/src/provider-selection/resolve-agent-form.test.ts
@@ -1477,3 +1477,16 @@ it("keeps a new model's thinking preference when pending fork defaults finish re
   });
   expect(ready.form).toEqual(edited.form);
 });
+
+it("preserves saved thinking when a legacy default-model fork resolves", () => {
+  const resolved = resolveFormState(
+    { provider: "codex", model: "default", thinkingOptionId: "low" },
+    { providerPreferences: { codex: { thinkingByModel: { "gpt-5.3-codex": "xhigh" } } } },
+    CODEX_MODELS,
+    INITIAL_USER_MODIFIED,
+    makeState().form,
+    codexProviderMap,
+  );
+  expect(resolved.model).toBe("gpt-5.3-codex");
+  expect(resolved.thinkingOptionId).toBe("low");
+});
diff --git a/packages/app/src/provider-selection/resolve-agent-form.ts b/packages/app/src/provider-selection/resolve-agent-form.ts
index 8db7c79d63..18915479d2 100644
--- a/packages/app/src/provider-selection/resolve-agent-form.ts
+++ b/packages/app/src/provider-selection/resolve-agent-form.ts
@@ -141,7 +141,11 @@ function resolveCanonicalModelId(
 ): string {
   const normalizedModelId = normalizeSelectedModelId(modelId);
   if (!normalizedModelId || !availableModels) return normalizedModelId;
-  return findModelByReference(availableModels, normalizedModelId)?.id ?? "";
+  const model = findModelByReference(availableModels, normalizedModelId);
+  if (model) return model.id;
+  // COMPAT(default-model-id): added in v0.7.2, remove after 2026-12-06.
+  // Older drafts used "default" before providers exposed concrete model IDs.
+  return normalizedModelId === "default" ? resolveDefaultModelId(availableModels) : "";
 }
 
 export function resolveEffectiveModel(
@@ -304,13 +308,6 @@ function resolveModelField(input: {
   if (!provider) return "";
   const initialModel = normalizeSelectedModelId(initialValues?.model);
   const preferredModel = normalizeSelectedModelId(providerPrefs?.model);
-  // COMPAT(default-model-id): added in v0.7.2, remove after 2026-12-06.
-  // Older drafts used "default" before providers exposed concrete model IDs.
-  if ((initialModel || preferredModel) === "default" && availableModels?.length) {
-    return (
-      findModelByReference(availableModels, "default")?.id || resolveDefaultModelId(availableModels)
-    );
-  }
   if (initialModel) {
     return !availableModels
       ? initialModel