Fix Autoblog OpenAI fallback by using a valid default text model

.env.example

@@ -39,7 +39,7 @@ CRON_SECRET=change-me-to-a-long-random-string
 #   openai = prefer OPENAI_API_KEY, fall back to Anthropic if needed
 #   anthropic = prefer ANTHROPIC_API_KEY, fall back to OpenAI if needed
 BACKEND_AI_PROVIDER=openai
-BACKEND_AI_OPENAI_MODEL=gpt-5.5
+BACKEND_AI_OPENAI_MODEL=gpt-5-mini
 ANTHROPIC_API_KEY=
 OPENAI_API_KEY=
 GEMINI_API_KEY=

lib/env.ts

@@ -31,7 +31,7 @@ export const env = {
   backendAiProvider:
     process.env.BACKEND_AI_PROVIDER ?? process.env.AI_TEXT_PROVIDER ?? "openai",
   backendAiOpenaiModel:
-    process.env.BACKEND_AI_OPENAI_MODEL ?? "gpt-5.5",
+    process.env.BACKEND_AI_OPENAI_MODEL ?? "gpt-5-mini",
   anthropicApiKey: process.env.ANTHROPIC_API_KEY ?? "",
   openaiApiKey: process.env.OPENAI_API_KEY ?? "",
   geminiApiKey: process.env.GEMINI_API_KEY ?? "",

tests/contract/env-backend-ai.test.ts

@@ -0,0 +1,21 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+
+const originalBackendAiOpenaiModel = process.env.BACKEND_AI_OPENAI_MODEL;
+
+afterEach(() => {
+  vi.resetModules();
+  if (originalBackendAiOpenaiModel === undefined) {
+    delete process.env.BACKEND_AI_OPENAI_MODEL;
+    return;
+  }
+  process.env.BACKEND_AI_OPENAI_MODEL = originalBackendAiOpenaiModel;
+});
+
+describe("backend ai env defaults", () => {
+  it("defaults OpenAI Autoblog model to gpt-5-mini", async () => {
+    delete process.env.BACKEND_AI_OPENAI_MODEL;
+    vi.resetModules();
+    const { env } = await import("@/lib/env");
+    expect(env.backendAiOpenaiModel).toBe("gpt-5-mini");
+  });
+});