# Streaming Chat API Contract

This document defines the server-sent events (SSE) contract for chat completions.

Endpoint:
- `POST /v1/chat-completions/stream`

Transport:
- HTTP response uses `Content-Type: text/event-stream; charset=utf-8`
- Events are emitted in SSE format (`event: ...`, `data: ...`)
- Request body is JSON
- Request body supports the same inline attachment schema and limits documented in `docs/api/rest.md`.

Authentication:
- Same as REST endpoints (`Authorization: Bearer <token>` when token mode is enabled)

## Request Body

```json
{
  "chatId": "optional-chat-id",
  "provider": "openai|anthropic|xai",
  "model": "string",
  "messages": [
    {
      "role": "system|user|assistant|tool",
      "content": "string",
      "name": "optional",
      "attachments": [
        {
          "kind": "image",
          "id": "attachment-id",
          "filename": "photo.jpg",
          "mimeType": "image/jpeg",
          "sizeBytes": 12345,
          "dataUrl": "data:image/jpeg;base64,..."
        },
        {
          "kind": "text",
          "id": "attachment-id",
          "filename": "notes.md",
          "mimeType": "text/markdown",
          "sizeBytes": 4567,
          "text": "# Notes\\n...",
          "truncated": false
        }
      ]
    }
  ],
  "temperature": 0.2,
  "maxTokens": 256
}
```

Notes:
- If `chatId` is omitted, backend creates a new chat.
- If `chatId` is provided, backend validates it exists.
- Backend stores only new non-assistant input history rows to avoid duplicates.
- Attachments are optional and are persisted under `message.metadata.attachments` on stored user messages.

## Event Stream Contract

Event order:
1. Exactly one `meta`
2. Zero or more `tool_call`
3. Zero or more `delta`
4. Exactly one terminal event: `done` or `error`

### `meta`

```json
{
  "type": "meta",
  "chatId": "chat-id",
  "callId": "llm-call-id",
  "provider": "openai",
  "model": "gpt-4.1-mini"
}
```

### `delta`

```json
{ "type": "delta", "text": "next chunk" }
```

`text` may contain partial words, punctuation, or whitespace.

### `tool_call`

```json
{
  "toolCallId": "call_123",
  "name": "web_search",
  "status": "completed",
  "summary": "Performed web search for 'latest CPI release'.",
  "args": { "query": "latest CPI release" },
  "startedAt": "2026-03-02T10:00:00.000Z",
  "completedAt": "2026-03-02T10:00:00.820Z",
  "durationMs": 820,
  "error": null,
  "resultPreview": "{\"ok\":true,...}"
}
```

### `done`

```json
{
  "type": "done",
  "text": "full assistant response",
  "usage": {
    "inputTokens": 123,
    "outputTokens": 456,
    "totalTokens": 579
  }
}
```

`usage` may be omitted when provider does not expose final token accounting for stream mode.

### `error`

```json
{ "type": "error", "message": "provider timeout" }
```

## Provider Streaming Behavior

- `openai`/`xai`: backend may execute internal tool calls (`web_search`, `fetch_url`, optional `codex_exec`, and optional `shell_exec`) before producing final text.
- `openai`: image attachments are sent as chat-completions content parts; text attachments are inlined as text parts.
- `xai`: same attachment behavior as OpenAI.
- `anthropic`: streamed via event stream; emits `delta` from `content_block_delta` with `text_delta`. Image attachments are sent as base64 `image` blocks and text attachments are appended as `text` blocks.
- `web_search` uses `CHAT_WEB_SEARCH_ENGINE` (`exa` default, or `searxng` with `SEARXNG_BASE_URL` set). SearXNG mode requires the instance to allow `format=json`. This only affects chat-mode tool calls, not search-mode endpoints.
- `codex_exec` is available only when `CHAT_CODEX_TOOL_ENABLED=true`. It SSHes to `CHAT_CODEX_REMOTE_HOST`, creates/uses `CHAT_CODEX_REMOTE_WORKDIR`, and runs `codex exec --skip-git-repo-check <non-interactive wrapped prompt>` there with SSH stdin closed. Prefer `CHAT_CODEX_SSH_KEY_PATH` with a read-only mounted private key; `CHAT_CODEX_SSH_PRIVATE_KEY_B64` is also supported.
- `shell_exec` is available only when `CHAT_SHELL_TOOL_ENABLED=true`. It uses the same devbox SSH configuration, starts in `CHAT_CODEX_REMOTE_WORKDIR`, and runs non-interactive shell commands there with SSH stdin closed, not inside the Sybil server container.
- `CHAT_MAX_TOOL_ROUNDS` controls how many model/tool result cycles may occur before the backend returns a tool-call limit message; default is 8.

Tool-enabled streaming notes (`openai`/`xai`):
- Stream still emits standard `meta`, `delta`, `done|error` events.
- Stream may emit `tool_call` events while tool calls are executed.
- `delta` events stream incrementally as text is generated.

## Persistence + Consistency Model

Backend database remains source of truth.

During stream:
- Client may optimistically render accumulated `delta` text.

On successful completion:
- Backend persists assistant `Message` and updates `LlmCall` usage/latency in a transaction.
- Backend then emits `done`.

On failure:
- Backend records call error and emits `error`.

Client recommendation (for iOS/web):
1. Render deltas in real time for UX.
2. On `done`, refresh chat detail from REST (`GET /v1/chats/:chatId`) and use DB-backed data as canonical.
3. On `error`, preserve user input and show retry affordance.

## SSE Parsing Rules

- Concatenate multiple `data:` lines with newline before JSON parse.
- Event completes on blank line.
- Ignore unknown event names for forward compatibility.

## Example Stream

```text
event: meta
data: {"type":"meta","chatId":"c1","callId":"k1","provider":"openai","model":"gpt-4.1-mini"}

event: delta
data: {"type":"delta","text":"Hello"}

event: delta
data: {"type":"delta","text":" world"}

event: done
data: {"type":"done","text":"Hello world"}

```