fix(core): preserve provider session failures

packages/llm/test/provider/openai-responses.test.ts

@@ -1326,7 +1326,14 @@ describe("OpenAI Responses route", () => {
       // sometimes-generic provider message. The bare message alone meant
       // production errors like rate limits were indistinguishable from
       // unrelated stream failures.
-      expect(response.events).toEqual([{ type: "provider-error", message: "rate_limit_exceeded: Slow down" }])
+      expect(response.events).toEqual([
+        {
+          type: "provider-error",
+          message: "rate_limit_exceeded: Slow down",
+          category: "rate-limit",
+          retryable: true,
+        },
+      ])
     }),
   )