fix(ai): track the ChatGPT Codex backend's current model slugs

The ChatGPT Codex backend rotated its ChatGPT-auth model slugs off the
`-codex` specialist line onto the plain `gpt-5.x` line, so the in-code
default ladder (`gpt-5.3-codex`, `gpt-5-codex`, `gpt-5`, `gpt-4o`) is
now rejected and insight generation fails with a 503 on a fresh deploy
that has no `CODEX_MODEL_FALLBACK_CHAIN` override.

Replace the default ladder with the current accepted set, in order:
`gpt-5.5` (current default across paid tiers), `gpt-5.4` and
`gpt-5.4-mini` (documented fallbacks), `gpt-5.3-codex` (late rung, still
accepted intermittently), `gpt-5.2` (legacy floor). The
fall-through-on-rejection walk, the working-slug cache, and the env
override path are unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
(cherry picked from commit bced19de2d4f0788bfd6fa56a78e719347776a1f)

src/lib/ai/__tests__/codex-slug-fallback.test.ts

@@ -337,6 +337,39 @@ describe("Codex slug fallback chain", () => {
     expect(helper(400, "unrelated 400")).toBe(false);
   });
 
+  it("DEFAULT_SLUG_FALLBACK_CHAIN tracks the current ChatGPT-auth ladder", () => {
+    // The backend rotated its ChatGPT-auth slugs onto the gpt-5.x line on
+    // 2026-06-02; the in-code default must match the accepted set, in order.
+    expect([...__test.DEFAULT_SLUG_FALLBACK_CHAIN]).toEqual([
+      "gpt-5.5",
+      "gpt-5.4",
+      "gpt-5.4-mini",
+      "gpt-5.3-codex",
+      "gpt-5.2",
+    ]);
+  });
+
+  it("loadFallbackChain falls back to the default ladder with no env override", () => {
+    const origModel = process.env.CODEX_MODEL;
+    const origChain = process.env.CODEX_MODEL_FALLBACK_CHAIN;
+    delete process.env.CODEX_MODEL;
+    delete process.env.CODEX_MODEL_FALLBACK_CHAIN;
+    try {
+      expect(__test.loadFallbackChain()).toEqual([
+        "gpt-5.5",
+        "gpt-5.4",
+        "gpt-5.4-mini",
+        "gpt-5.3-codex",
+        "gpt-5.2",
+      ]);
+    } finally {
+      if (origModel === undefined) delete process.env.CODEX_MODEL;
+      else process.env.CODEX_MODEL = origModel;
+      if (origChain === undefined) delete process.env.CODEX_MODEL_FALLBACK_CHAIN;
+      else process.env.CODEX_MODEL_FALLBACK_CHAIN = origChain;
+    }
+  });
+
   it("loadFallbackChain folds CODEX_MODEL into position 0", () => {
     const orig = process.env.CODEX_MODEL;
     process.env.CODEX_MODEL = "custom-pinned-slug";
@@ -344,7 +377,7 @@ describe("Codex slug fallback chain", () => {
       const chain = __test.loadFallbackChain();
       expect(chain[0]).toBe("custom-pinned-slug");
       // Defaults still present after position 0.
-      expect(chain).toContain("gpt-5.3-codex");
+      expect(chain).toContain("gpt-5.5");
       // No duplicates.
       const seen = new Set(chain);
       expect(seen.size).toBe(chain.length);

src/lib/ai/codex-client.ts

@@ -33,16 +33,23 @@ import {
 const CODEX_ENDPOINT = "https://chatgpt.com/backend-api/codex/responses";
 
 /**
- * Default fallback chain — most-current-first as of 2026-05-09. Override
+ * Default fallback chain — most-current-first as of 2026-06-02. Override
  * via `CODEX_MODEL_FALLBACK_CHAIN` (comma-separated) on apps01 if a
  * specific plan ladder needs different ordering. `CODEX_MODEL` is
  * folded into position 0 of the chain when set; duplicates are dropped.
+ *
+ * The ChatGPT Codex backend rotated its ChatGPT-auth slugs off the
+ * `-codex` specialist line onto the plain `gpt-5.x` line on 2026-06-02;
+ * the former `-codex` defaults are now rejected with a 503 "all
+ * configured Codex slugs were rejected". The ladder below tracks the
+ * current accepted set.
  */
 const DEFAULT_SLUG_FALLBACK_CHAIN = [
-  "gpt-5.3-codex", // verified accepted on Plus/Pro 2026-05-09
-  "gpt-5-codex", // historical default — kept as second-chance retry; backend may flip back
-  "gpt-5", // bare slug — rejected on ChatGPT-auth as of 2026-05; safe to keep as ladder-rung
-  "gpt-4o", // last-ditch capability fallback
+  "gpt-5.5", // current default across paid tiers as of 2026-06-02
+  "gpt-5.4", // documented fallback
+  "gpt-5.4-mini", // documented lighter-weight fallback
+  "gpt-5.3-codex", // late rung — still accepted intermittently
+  "gpt-5.2", // legacy floor
 ] as const;
 
 function loadFallbackChain(): string[] {