CommandCode returns errors as a type:"error" event inside an HTTP 200
NDJSON stream instead of a non-200 status, so the existing combo/account
fallback logic (keyed off response.status) never triggered and the error
text was streamed to the client as if it were content.
Peek the first NDJSON events before committing to a stream; on a
type:"error" event, abort and return a proper 4xx/5xx Response instead.
Normal streams are replayed losslessly (buffered prefix + rest of the
stream) through the existing translator, so the happy path is unchanged.
Add CommandCodeExecutor.parseError() so parseUpstreamError() can extract
a clean message/status from the synthesized error body.
- new open-sse/utils/streamErrorPeek.js: bounded peek of the first bytes of a
200 stream; configured pattern match → 502 so account/combo fallback can run
before any byte reaches the client (streaming included). Re-emits RAW bytes
so split multi-byte UTF-8 sequences survive the peek (never re-encode
decoded text — TextDecoder flush corrupts a lone leading byte to U+FFFD).
- chatCore: run the peek after executor.execute when the provider has
streamErrorPatterns configured; chat.js passes the settings through.
- commandcode executor: same raw-bytes fix in peekForUpstreamError + regression
test that fails against the old flush-based re-encode.
Upstream emits AI SDK v5 {"type":"error"} events inside an HTTP 200 stream.
The translator turned them into fake success content ([CommandCode error: ...]
+ finish_reason stop), so account/model fallback never fired and logs showed
Status: success.
- translator: error events now emit an OpenAI-shaped error chunk (chunk.error)
instead of content; parseSSEToOpenAIResponse already detects chunk?.error
- executor: peek the first events before committing the response; an early
error event returns 502 so fallback runs before any byte reaches the client
CommandCode upstream only speaks NDJSON streaming; the executor always
wraps it as OpenAI SSE. Force body.stream=true so non-stream client
requests still produce a parseable upstream stream (router aggregates
SSE→JSON downstream).
Co-authored-by: Cursor <cursoragent@cursor.com>
