# `POST /modelconversation/{id}/message`

Protected. Requires a valid session cookie (`credentials: 'include'`).

Post a user message

Appends a message with role `user` to the conversation.
Refused with 409 unless the conversation state is `idle`.


## Path parameters

| Param | Required | Type | Description |
|-------|----------|------|-------------|
| `id` | yes | integer | Conversation ID |

## Body (JSON)

| Field | Required | Type | Description |
|-------|----------|------|-------------|
| `message` | no | string | User message text or fallback content |
| `role` | no | string | Message role ('user' or 'tool') |
| `tool_call_id` | no | string | Target tool call ID when responding to a tool like ask_user |
| `content` | no |  | Tool response content payload |
| `answer` | no |  | Shorthand answer for ask_user response |

```json
{
  "message": "…",
  "role": "user",
  "tool_call_id": "…",
  "content": "…",
  "answer": "…"
}
```

## Signals

On success, emits SSE signal: `modelconversation-<id>` (see [`GET /events`](../events.md)).

## Response `201`

Created message

```json
{
  "message": {
    "id": 1,
    "conversation_id": 1,
    "created_at": "…",
    "role": "system",
    "message": "…"
  }
}
```

## Errors

| Status | Description |
|--------|-------------|
| 400 | Invalid ID, empty message or no company selected — `{"error":"…"}` |
| 401 | Unauthorized — `{"error":"…"}` |
| 403 | Not authorized — `{"error":"…"}` |
| 404 | Conversation not found — `{"error":"…"}` |
| 409 | Conversation is not idle — `{"error":"…"}` |

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