Stream translation

cursor-agent --output-format stream-json writes one JSON object per line. OpenCode expects OpenAI-compatible server-sent events. The proxy parses each line, classifies the event, and emits the corresponding SSE chunk.

The mixed stream

Cursor output can contain both:

• raw partial deltas, where each event contains only new text;
• accumulated snapshots, where each event repeats everything produced so far.

Treating every event as a delta duplicates snapshots. Treating every event as a snapshot drops real deltas. MixedDeltaTracker handles both in one stream.

Delta detection

Current Cursor events give the parser a practical signal:

• a timestamped event without model_call_id is treated as a partial delta;
• an event carrying model_call_id is treated as an accumulated snapshot, even when its subtype says delta.

This is based on observed cursor-agent output. It can change when Cursor changes the protocol, which is why the parser keeps tests for mixed event shapes.

Snapshot reconciliation

For a snapshot, the tracker compares it with text already emitted:

1. If the snapshot starts with the emitted text, emit only the new suffix.
2. If the emitted text starts with the snapshot, emit nothing. This covers a duplicate or shorter snapshot.
3. If neither is a prefix, emit the current snapshot. This preserves content after an unexpected rewrite instead of guessing an overlap.

Text and thinking use separate buffers. A tool-call start resets both because the next assistant phase is a new stream segment.

SSE output

Text becomes:

{
  "choices": [
    {
      "delta": {
        "content": "new text"
      }
    }
  ]
}

Thinking uses reasoning_content. Tool events become OpenAI tool_calls with the Cursor call ID, normalised name, and JSON arguments.

The final result event may add token usage. When Cursor omits usage, the proxy omits it too rather than inventing zeros.

Malformed lines

Blank or non-object lines are ignored. Invalid JSON is logged at debug level with a short prefix and does not crash the whole stream.

A cut-off response needs the raw debug log because the failure can sit in four places: the Cursor process, NDJSON parsing, event reconciliation, or the SSE consumer. See Troubleshooting.

Relevant source

• src/streaming/parser.ts
• src/streaming/types.ts
• src/streaming/delta-tracker.ts
• src/streaming/openai-sse.ts
• src/streaming/ai-sdk-parts.ts