feat(sdk,core): preserve chat.agent context after cancel / OOM / crash (#3671)

Author: ericallam

apps/webapp/test/replay-after-crash.test.ts

@@ -55,16 +55,19 @@ function textTurn(id: string, text: string): UIMessageChunk[] {
  *     via the webapp's real `generatePresignedUrl` (so snapshot reads
  *     hit a real S3-compatible backend).
  *   - `readSessionStreamRecords` returns the canonical
- *     `{ records: [{ data, id, seqNum }] }` shape — `data` is the
- *     JSON-encoded chunk body, mirroring the webapp's S2 record shape.
+ *     `{ records: [{ data, id, seqNum }] }` shape. `data` is the parsed
+ *     chunk OBJECT — the SDK writer puts the chunk object directly into
+ *     the record envelope and the webapp route forwards it as-is, so
+ *     the schema now declares `data: z.unknown()` and consumers use it
+ *     without an extra `JSON.parse` step.
  */
 function stubApiClient(opts: {
   projectRef: string;
   envSlug: string;
   sessionOutChunks: unknown[];
 }) {
   const records = opts.sessionOutChunks.map((chunk, i) => ({
-    data: typeof chunk === "string" ? chunk : JSON.stringify(chunk),
+    data: chunk,
     id: `evt-${i + 1}`,
     seqNum: i + 1,
   }));

packages/core/src/v3/schemas/api.ts

@@ -1995,14 +1995,21 @@ export type SendInputStreamResponseBody = z.infer<typeof SendInputStreamResponse
  * Response body for `GET /realtime/v1/sessions/:id/:io/records`. A non-SSE,
  * `wait=0` drain of a session channel — used at run boot for snapshot
  * replay where the SSE long-poll tax (~1s on empty streams) was the
- * dominant cost. The shape mirrors the webapp's internal `StreamRecord`
- * type (`apps/webapp/app/services/realtime/types.ts`); each record's
- * `data` is a JSON-encoded chunk body that callers parse client-side.
+ * dominant cost.
+ *
+ * `data` is the parsed chunk body (the SDK writer puts the chunk object
+ * directly into the S2 record envelope; the route unwraps the envelope
+ * and forwards the inner object as-is). Callers use it directly — no
+ * additional JSON.parse step. Schema is `z.unknown()` because chunk
+ * shape varies by `chunk.type` (the AI SDK's `UIMessageChunk`
+ * discriminated union plus Trigger control records); consumers
+ * already runtime-check on the discriminator and tolerate malformed
+ * records by skipping them.
  */
 export const ReadSessionStreamRecordsResponseBody = z.object({
   records: z.array(
     z.object({
-      data: z.string(),
+      data: z.unknown(),
       id: z.string(),
       seqNum: z.number(),
     })