fix(runtime-fallback): add session messages extractor

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/runtime-fallback/session-messages.ts

@@ -0,0 +1,38 @@
+export type SessionMessagePart = {
+  type?: string
+  text?: string
+}
+
+export type SessionMessage = {
+  info?: Record<string, unknown>
+  parts?: SessionMessagePart[]
+}
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null
+}
+
+function isSessionMessage(value: unknown): value is SessionMessage {
+  return isRecord(value)
+}
+
+function isSessionMessageArray(value: unknown): value is SessionMessage[] {
+  return Array.isArray(value) && value.every(isSessionMessage)
+}
+
+export function extractSessionMessages(messagesResponse: unknown): SessionMessage[] | undefined {
+  if (isSessionMessageArray(messagesResponse)) {
+    return messagesResponse
+  }
+
+  if (!isRecord(messagesResponse)) {
+    return undefined
+  }
+
+  const data = messagesResponse.data
+  if (isSessionMessageArray(data)) {
+    return data
+  }
+
+  return undefined
+}