> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hill90.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Send message in thread

> Sends a user message and dispatches work to the agent.
Pre-checks: agent running, concurrency guard, elevated scope check.




## OpenAPI

````yaml /ai-app/openapi.yaml post /chat/threads/{id}/messages
openapi: 3.0.3
info:
  title: Hill90 API
  description: Hill90 platform API — agent management and lifecycle operations.
  version: 0.1.0
servers:
  - url: /
    description: Relative (behind Traefik reverse proxy)
security: []
paths:
  /chat/threads/{id}/messages:
    parameters:
      - name: id
        in: path
        required: true
        schema:
          type: string
          format: uuid
    post:
      summary: Send message in thread
      description: |
        Sends a user message and dispatches work to the agent.
        Pre-checks: agent running, concurrency guard, elevated scope check.
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              required:
                - message
              properties:
                message:
                  type: string
                idempotency_key:
                  type: string
                  nullable: true
      responses:
        '201':
          description: Message sent
          content:
            application/json:
              schema:
                type: object
                properties:
                  message_id:
                    type: string
                    format: uuid
        '400':
          description: Missing or invalid fields
        '403':
          description: Elevated scope requires admin role
        '404':
          description: Thread not found or not a participant
        '409':
          description: Agent not running, concurrency guard, or duplicate
      security:
        - bearerAuth: []
components:
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      bearerFormat: JWT

````