Reject model IDs unsafe for headers and clarify supported capabilities

test/provider.test.ts

@@ -58,6 +58,20 @@ test("skips unusable entries but rejects malformed or entirely unusable catalogs
   }
 });
 
+test("catalog IDs must fit Fetch's Latin-1 header values", () => {
+  const valid = ["gpt-4o", "model-\u00ff"];
+  const invalid = ["model-\u0100", "model-\u{1f600}", "model-\ud800"];
+  const parsed = parseCatalog({ data: [...valid, ...invalid].map((id) => ({ id })) });
+  assert.deepEqual(parsed, { ids: valid, skipped: invalid.length });
+  for (const id of parsed.ids) {
+    const headers = new Headers(makeModel(id, BASE_URL).headers);
+    assert.equal(headers.get("deployment-id"), id);
+  }
+  for (const id of invalid) {
+    assert.throws(() => parseCatalog({ data: [{ id }] }), /without any valid model IDs/);
+  }
+});
+
 const known: Record<string, ModelMetadata> = {
   "model-a": { name: "Model A", input: ["text", "image"], contextWindow: 272_000, maxTokens: 128_000 },
 };