Sumika

Sumika (住処), from the Japanese word for "dwelling," is a stateful API server that acts as a bridge for agents compatible with the Agent Client Protocol (ACP), such as the Gemini CLI. It provides a persistent, multi-session chat interface with support for tool calls and streaming events.

Core Concepts

Sumika is built around two primary concepts:

• Workspaces: A Workspace is the primary data model for isolating an agent's context. It maps a unique ID to a directory on the filesystem, either managed by Sumika (~/.sumika/workspaces/<workspace-id>) or a custom user-provided path. A Workspace is a persistent entity that holds configuration (like environment variables and MCP servers) and contains multiple Sessions.
• Sessions: A Session represents a single, stateful conversation with an agent. It's a persistent JSON object containing the full message history, including user prompts, agent responses, and tool calls. Each Session is mapped to a live, underlying ACP process. If the agent process terminates, the Session becomes disconnected but retains its history, allowing it to be re-initialized into a new process without data loss.

Getting Started

Prerequisites

• Node.js
• pnpm

Installation

1. Clone the repository.
2. Navigate to the server directory:

   cd server

3. Install dependencies:

   pnpm install

4. Create a .env file from the example:

   cp .env.example .env

5. Add your GEMINI_API_KEY to the .env file.

Configuration

You can configure the server using the following environment variables in your .env file:

• GEMINI_API_KEY (Required): Your API key for the Gemini service.
• GEMINI_MODEL (Optional): The specific Gemini model to use (e.g., gemini-2.5-pro). Defaults to the Gemini CLI's default model if not set.
• SUMIKA_ROOT_DIR (Optional): By default, Sumika stores all workspaces and session data in ~/.sumika. You can specify a different root directory by setting this variable to an absolute path.

Custom Agent and Environment Variables

For advanced use cases, you can configure Sumika to launch a custom ACP-compliant agent or to inject global environment variables into the agent's process. This is managed via the ~/.sumika/settings.json file.

• customAcpCommand (string): A shell command used to launch your custom agent. If this is blank or omitted, Sumika defaults to using the built-in @google/gemini-cli.
• env (object): A key-value map of environment variables to set in the agent's process. These will override any system-level variables with the same name.

Example settings.json:

{
  "customAcpCommand": "/path/to/my-custom-agent --acp --verbose",
  "env": {
    "CUSTOM_AGENT_API_KEY": "your-secret-api-key"
  },
  "mcpServers": {}
}

Note: The Sumika server must be restarted for any changes to settings.json to take effect.

Running the Server

To start the development server, run:

pnpm dev

The API will be available at http://localhost:8787. Interactive OpenAPI documentation is available at http://localhost:8787/docs.

Global MCP Servers

Sumika supports global MCP servers configured at ~/.sumika/settings.json in addition to per-workspace servers. When creating or reinitializing a session, Sumika merges the two sets and sends the merged list to the ACP agent. If both define the same server name, the workspace definition takes precedence.

Example ~/.sumika/settings.json:

{
  "mcpServers": {
    "serverName": {
      "command": "npx",
      "args": ["serverName"],
      "env": { "ENV_VAR": "1" }
    }
  }
}

API

• GET /api/settings → Returns the global settings.
• PUT /api/settings → Replaces the global settings (full-replace semantics). Payload shape matches the example above.

Notes:

• Settings are validated and written atomically. If a corrupt file is detected, the original is backed up to settings.json.bak and reset.
• Changes take effect for new or reinitialized sessions.