# cursor-adapter SSE Diagnostic Results

> **Status: RESOLVED 2026-04-18.** This file is kept for history. The bugs
> listed below have been fixed. Current behavior is captured by regression
> tests in `internal/server/messages_test.go` and `internal/converter/convert_test.go`.

---

## Originally reported (2026-04-15)

When used as an OpenAI-compatible endpoint for SDKs like
`@ai-sdk/openai-compatible` (OpenCode), cursor-adapter had five issues:

1. **Non-streaming is completely broken** — server hung for 30s and never
   wrote a response body.
2. **SSE content was double-JSON-encoded** — each `delta.content` field
   held the *entire* Cursor CLI JSON line (including `type:"system"`,
   `type:"user"`, `type:"result"`) serialized as a string, instead of plain
   assistant text.
3. **Missing `role` in first delta.**
4. **Missing `finish_reason` in final chunk.**
5. **Usage not at the top level** — embedded inside a stringified JSON
   payload instead of `chunk.usage`.

---

## Root cause

Two separate bugs plus one latent one, all landed together:

- **Non-stream hang / `exit status 1`:** the chat-only isolation ported from
  `cursor-api-proxy` was overriding `HOME` → temp dir. On macOS with
  keychain login, the `agent` CLI resolves its session token via
  `~/.cursor/` + the real keychain, so a fake `HOME` made `agent` exit
  immediately with "Authentication required. Please run 'agent login'".
  The adapter surfaced this as either a hang (when timeouts swallowed the
  exit) or as `exit status 1` once the error bubbled up.
- **Content wrapping / leaked system-user chunks:** older pre-parser code
  forwarded raw Cursor JSON lines as `delta.content`. The parser had
  already been rewritten by the time this diagnostic was taken, but the
  report caught an earlier build.
- **Duplicate final delta (discovered during this pass):** the stream
  parser's accumulator was *reassigned* (`p.accumulated = content`) even
  when the new fragment did not start with the accumulated prefix. With
  Cursor CLI's incremental output mode (one fragment per message), that
  meant the "you said the full text" final message looked different from
  accumulated and was emitted as a second copy of the whole response.

---

## Fix summary

- `internal/workspace/workspace.go` — only override `CURSOR_CONFIG_DIR` by
  default. `HOME`/`XDG_CONFIG_HOME`/`APPDATA` are only isolated when
  `CURSOR_API_KEY` is set (which bypasses keychain auth anyway).
- `internal/converter/convert.go` — stream parser now handles both
  cumulative and incremental Cursor output modes. In the non-prefix
  branch it appends to accumulated instead of replacing it, so the final
  duplicate is correctly detected via `content == accumulated` and
  skipped.
- `internal/server/handlers.go` + `anthropic_handlers.go` — already emit
  `role:"assistant"` in the first delta, `finish_reason:"stop"` in the
  final chunk, and `usage` at the top level. Regression tests added to
  `messages_test.go` lock this in.

## Verified manually

```
$ curl -sN http://localhost:8765/v1/chat/completions \
    -H 'Content-Type: application/json' \
    -d '{"model":"auto","stream":true,"messages":[{"role":"user","content":"count 1 to 5"}]}'

data: {"id":"chatcmpl-…","choices":[{"index":0,"delta":{"role":"assistant"},"finish_reason":null}]}
data: {"id":"chatcmpl-…","choices":[{"index":0,"delta":{"content":"\n1、2、3、4、5。"},"finish_reason":null}]}
data: {"id":"chatcmpl-…","choices":[{"index":0,"delta":{},"finish_reason":"stop"}],"usage":{"prompt_tokens":6,"completion_tokens":5,"total_tokens":11}}
data: [DONE]
```

Non-streaming returns `chat.completion` JSON with `stop_reason:"stop"` and
`usage` populated. Anthropic `/v1/messages` emits `message_start` →
`content_block_delta*` → `message_stop` without duplicating the final
cumulative fragment.