[Bug] Non-streaming retry receives event-stream response instead of JSON (HTTP 200)

**Bug Description**
API Error: API returned an empty or malformed response (HTTP 200) — check for a proxy or gateway intercepting the request. Response: content-type event-stream, body is an event stream (the non-streaming request was answered with a stream), 3935 bytes, request-id req_011CeFKxwXG5NNna6Ute7Nmz, server cloudflare, intermediary headers anthropic-* cf-cache-status cf-ray. This was the non-streaming retry of streaming request (no Anthropic request-id), which failed with: other; 0 stream events received.

**Environment Info**
- Platform: win32
- Terminal: windows-terminal
- Version: 2.1.238
- Feedback ID: 11f61404-1140-47bb-92bb-05785dab1d09

**Errors**
```json
[{"error":"UnexpectedApiResponseError: API returned an empty or malformed response (HTTP 200) — check for a proxy or gateway intercepting the request. Response: content-type event-stream, body is an event stream (the non-streaming request was answered with a stream), 3935 bytes, request-id req_011CeFKxwXG5NNna6Ute7Nmz, server cloudflare, intermediary headers anthropic-* cf-cache-status cf-ray. This was the non-streaming retry of streaming request (no Anthropic request-id), which failed with: other; 0 stream events received.\n at (B:/~BUN/root/cli:21840:9380)\n at processTicksAndRejections (native:7:39)","timestamp":"2026-08-21T05:18:00.311Z"}]
```

The payload names only the bundled CLI location B:/~BUN/root/cli:21840:9380; start by reproducing the non-streaming retry with the recorded response details and tracing that retry path. Done means the retry handles the received event-stream response appropriately instead of reporting an empty or malformed JSON response, while the streaming-failure case remains covered.

索引モデルが issue の本文から書いたものです。