fix(api): don't force combo names to codex/ on /v1/responses (#3227, #3233) (#3244)

The Codex CLI WS->HTTP fallback rewrite (resolveResponsesApiModel) prefixes a
bare model id with codex/ whenever codex/<id> resolves to codex. Codex accepts
arbitrary model strings, so a combo name with no slash (e.g. n8n-text,
paid-premium) was rewritten to codex/<combo> and sent to Codex instead of being
resolved as a combo — regressing combos via /v1/responses in v3.8.9+. Skip the
rewrite when the bare id is a combo (getComboByName). + unit test.

tests/unit/responses-combo-resolution-3227.test.ts

@@ -0,0 +1,45 @@
+/**
+ * #3227 / #3233 — combo names broke on /v1/responses in v3.8.9+.
+ *
+ * The Codex CLI WS→HTTP fallback added `resolveResponsesApiModel`, which rewrites a bare
+ * model id to `codex/<id>` whenever `codex/<id>` resolves to the codex provider. Codex
+ * accepts ANY model string, so a *combo* name with no slash (e.g. `n8n-text`,
+ * `paid-premium`) was force-rewritten to `codex/<combo>` and sent to Codex —
+ * "No credentials for provider: codex" / "model not supported" — instead of being
+ * resolved as a combo. The fix skips the codex rewrite when the bare name is a combo.
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { resolveResponsesApiModel } from "../../src/app/api/internal/codex-responses-ws/modelResolution.ts";
+
+// Resolver where bare ids resolve to a non-codex default, but codex accepts anything
+// (mirrors real getModelInfo: the codex provider passes arbitrary model strings).
+const resolver = async (modelStr: string) => {
+  if (modelStr.startsWith("codex/")) return { provider: "codex", model: modelStr.slice(6) };
+  if (modelStr === "gpt-5.5") return { provider: "openrouter", model: "gpt-5.5" };
+  return { provider: "openrouter", model: modelStr };
+};
+
+test("a bare combo name is NOT rewritten to codex/ (it must resolve as a combo)", async () => {
+  const isCombo = async (name: string) => name === "n8n-text" || name === "paid-premium";
+
+  for (const combo of ["n8n-text", "paid-premium"]) {
+    const out = await resolveResponsesApiModel(combo, resolver, isCombo);
+    assert.equal(out.changed, false, `${combo} must not be codex-prefixed`);
+    assert.equal(out.model, combo);
+  }
+});
+
+test("a bare ChatGPT model id is still codex-preferred (Codex CLI WS→HTTP fallback preserved)", async () => {
+  const isCombo = async () => false;
+  const out = await resolveResponsesApiModel("gpt-5.5", resolver, isCombo);
+  assert.equal(out.changed, true);
+  assert.equal(out.model, "codex/gpt-5.5");
+});
+
+test("provider-prefixed ids pass through unchanged", async () => {
+  const out = await resolveResponsesApiModel("anthropic/claude-opus-4-8", resolver, async () => false);
+  assert.equal(out.changed, false);
+  assert.equal(out.model, "anthropic/claude-opus-4-8");
+});