fix: defensive SDK response handling & parts-reader normalization

- Replace all response.data ?? [] with (response.data ?? response)
  pattern across 14 files to handle SDK array-shaped responses
- Normalize SDK parts in parts-reader.ts by injecting sessionID/
  messageID before validation (P1: SDK parts lack these fields)
- Treat unknown part types as having content in
  recover-empty-content-message-sdk.ts to prevent false placeholder
  injection on image/file parts
- Replace local isRecord with shared import in parts-reader.ts

src/hooks/anthropic-context-window-limit-recovery/message-builder.ts

@@ -64,7 +64,7 @@ async function findEmptyMessageIdsFromSDK(
     const response = (await client.session.messages({
       path: { id: sessionID },
     })) as { data?: SDKMessage[] }
-    const messages = response.data ?? []
+    const messages = ((response.data ?? response) as unknown as SDKMessage[]) ?? []
 
     const emptyIds: string[] = []
     for (const message of messages) {