AI_JSONParseError during SSE streaming is not retried (falls to NamedError.Unknown) #13579

Description

When SSE streams from providers return malformed JSON (e.g., corrupted chunks from Kimi K2.5 via Kilo Gateway), the Vercel AI SDK throws AI_JSONParseError. In the current message-v2.ts:fromError() error classification chain, this error:

1. Is NOT an APICallError (skips that branch)
2. Is NOT a LoadAPIKeyError or DOMException (skips those branches)
3. Falls through to case e instanceof Error: → becomes NamedError.Unknown

Since NamedError.Unknown is not recognized as retryable by retry.ts:retryable(), the session terminates immediately instead of retrying.

Evidence

This was observed in production:

{
  "name": "AI_JSONParseError",
  "text": "{\"id\":\"chatcmpl-jQugNdata:{\"id\":\"chatcmpl-iU6vkr3fItZ0Y4rTCmIyAnXO\",...}"
}

The error is classified as UnknownError and the session stops:

{
  "type": "error",
  "error": {
    "name": "UnknownError",
    "data": {
      "message": "AI_JSONParseError: JSON parsing failed: ..."
    }
  }
}

How Other CLI Agents Handle This

OpenAI Codex CLI: Skips unparseable SSE events and continues. CodexErr::Json is retryable with up to 5 stream retries.

Qwen Code: SDK's parseJsonLineSafe() silently skips failed lines.

Proposed Fix

In message-v2.ts:fromError(), add detection before the generic instanceof Error fallback:

case e instanceof Error: {
  const message = e.message || e.toString();
  const isStreamParseError =
    e.name === 'AI_JSONParseError' ||
    message.includes('AI_JSONParseError') ||
    message.includes('JSON parsing failed');
  if (isStreamParseError) {
    return new MessageV2.StreamParseError(
      { message, isRetryable: true, text: (e as any).text },
      { cause: e }
    ).toObject();
  }
  // ... existing socket/timeout checks
}

Related Issues

• [Bug] JSON Parse Error with Zhipu GLM-4.7: Stream chunks are concatenated incorrectly #7692: JSON Parse Error with Zhipu GLM-4.7: Stream chunks concatenated incorrectly
• GLM 4.7 AI_JSONParseError #8431: GLM 4.7 AI_JSONParseError
• Error Writing Large Files (at least with Kimi K2.5) #10967: Error Writing Large Files with Kimi K2.5
• StreamText error handling still not working properly in v4.0.18 vercel/ai#4099: streamText error handling
• AI_JSONParseError should support retry for mid-stream parse errors vercel/ai#12595: AI_JSONParseError should support retry

See: link-assistant/agent#169