refactor: cron payload migration cleanup (#621)

* refactor: centralize cron payload migration

* test: stabilize block streaming mocks

* test: adjust chunker fence-close case

src/cron/payload-migration.ts

@@ -0,0 +1,38 @@
+type UnknownRecord = Record<string, unknown>;
+
+function readString(value: unknown): string | undefined {
+  if (typeof value !== "string") return undefined;
+  return value;
+}
+
+function normalizeProvider(value: string): string {
+  return value.trim().toLowerCase();
+}
+
+export function migrateLegacyCronPayload(payload: UnknownRecord): boolean {
+  let mutated = false;
+
+  const providerValue = readString(payload.provider);
+  const channelValue = readString(payload.channel);
+
+  const nextProvider =
+    typeof providerValue === "string" && providerValue.trim().length > 0
+      ? normalizeProvider(providerValue)
+      : typeof channelValue === "string" && channelValue.trim().length > 0
+        ? normalizeProvider(channelValue)
+        : "";
+
+  if (nextProvider) {
+    if (providerValue !== nextProvider) {
+      payload.provider = nextProvider;
+      mutated = true;
+    }
+  }
+
+  if ("channel" in payload) {
+    delete payload.channel;
+    mutated = true;
+  }
+
+  return mutated;
+}