Add ACP (Agent Client Protocol) support

packages/opencode/package.json

@@ -47,6 +47,7 @@
     "@opencode-ai/sdk": "workspace:*",
     "@parcel/watcher": "2.5.1",
     "@standard-schema/spec": "1.0.0",
+    "@zed-industries/agent-client-protocol": "0.4.5",
     "@zip.js/zip.js": "2.7.62",
     "ai": "catalog:",
     "chokidar": "4.0.3",

packages/opencode/src/acp/README.md

@@ -0,0 +1,164 @@
+# ACP (Agent Client Protocol) Implementation
+
+This directory contains a clean, protocol-compliant implementation of the [Agent Client Protocol](https://agentclientprotocol.com/) for opencode.
+
+## Architecture
+
+The implementation follows a clean separation of concerns:
+
+### Core Components
+
+- **`agent.ts`** - Implements the `Agent` interface from `@zed-industries/agent-client-protocol`
+  - Handles initialization and capability negotiation
+  - Manages session lifecycle (`session/new`, `session/load`)
+  - Processes prompts and returns responses
+  - Properly implements ACP protocol v1
+
+- **`client.ts`** - Implements the `Client` interface for client-side capabilities
+  - File operations (`readTextFile`, `writeTextFile`)
+  - Permission requests (auto-approves for now)
+  - Terminal support (stub implementation)
+
+- **`session.ts`** - Session state management
+  - Creates and tracks ACP sessions
+  - Maps ACP sessions to internal opencode sessions
+  - Maintains working directory context
+  - Handles MCP server configurations
+
+- **`server.ts`** - ACP server startup and lifecycle
+  - Sets up JSON-RPC over stdio using the official library
+  - Manages graceful shutdown on SIGTERM/SIGINT
+  - Provides Instance context for the agent
+
+- **`types.ts`** - Type definitions for internal use
+
+## Usage
+
+### Command Line
+
+```bash
+# Start the ACP server in the current directory
+opencode acp
+
+# Start in a specific directory
+opencode acp --cwd /path/to/project
+```
+
+### Programmatic
+
+```typescript
+import { ACPServer } from "./acp/server"
+
+await ACPServer.start()
+```
+
+### Integration with Zed
+
+Add to your Zed configuration (`~/.config/zed/settings.json`):
+
+```json
+{
+  "agent_servers": {
+    "OpenCode": {
+      "command": "opencode",
+      "args": ["acp"]
+    }
+  }
+}
+```
+
+## Protocol Compliance
+
+This implementation follows the ACP specification v1:
+
+✅ **Initialization**
+
+- Proper `initialize` request/response with protocol version negotiation
+- Capability advertisement (`agentCapabilities`)
+- Authentication support (stub)
+
+✅ **Session Management**
+
+- `session/new` - Create new conversation sessions
+- `session/load` - Resume existing sessions (basic support)
+- Working directory context (`cwd`)
+- MCP server configuration support
+
+✅ **Prompting**
+
+- `session/prompt` - Process user messages
+- Content block handling (text, resources)
+- Response with stop reasons
+
+✅ **Client Capabilities**
+
+- File read/write operations
+- Permission requests
+- Terminal support (stub for future)
+
+## Current Limitations
+
+### Not Yet Implemented
+
+1. **Streaming Responses** - Currently returns complete responses instead of streaming via `session/update` notifications
+2. **Tool Call Reporting** - Doesn't report tool execution progress
+3. **Session Modes** - No mode switching support yet
+4. **Authentication** - No actual auth implementation
+5. **Terminal Support** - Placeholder only
+6. **Session Persistence** - `session/load` doesn't restore actual conversation history
+
+### Future Enhancements
+
+- **Real-time Streaming**: Implement `session/update` notifications for progressive responses
+- **Tool Call Visibility**: Report tool executions as they happen
+- **Session Persistence**: Save and restore full conversation history
+- **Mode Support**: Implement different operational modes (ask, code, etc.)
+- **Enhanced Permissions**: More sophisticated permission handling
+- **Terminal Integration**: Full terminal support via opencode's bash tool
+
+## Testing
+
+```bash
+# Run ACP tests
+bun test test/acp.test.ts
+
+# Test manually with stdio
+echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":1}}' | opencode acp
+```
+
+## Design Decisions
+
+### Why the Official Library?
+
+We use `@zed-industries/agent-client-protocol` instead of implementing JSON-RPC ourselves because:
+
+- Ensures protocol compliance
+- Handles edge cases and future protocol versions
+- Reduces maintenance burden
+- Works with other ACP clients automatically
+
+### Clean Architecture
+
+Each component has a single responsibility:
+
+- **Agent** = Protocol interface
+- **Client** = Client-side operations
+- **Session** = State management
+- **Server** = Lifecycle and I/O
+
+This makes the codebase maintainable and testable.
+
+### Mapping to OpenCode
+
+ACP sessions map cleanly to opencode's internal session model:
+
+- ACP `session/new` → creates internal Session
+- ACP `session/prompt` → uses SessionPrompt.prompt()
+- Working directory context preserved per-session
+- Tool execution uses existing ToolRegistry
+
+## References
+
+- [ACP Specification](https://agentclientprotocol.com/)
+- [TypeScript Library](https://github.com/zed-industries/agent-client-protocol/tree/main/typescript)
+- [Protocol Examples](https://github.com/zed-industries/agent-client-protocol/tree/main/typescript/examples)

packages/opencode/src/acp/agent.ts

@@ -0,0 +1,141 @@
+import type {
+  Agent,
+  AgentSideConnection,
+  AuthenticateRequest,
+  AuthenticateResponse,
+  CancelNotification,
+  InitializeRequest,
+  InitializeResponse,
+  LoadSessionRequest,
+  LoadSessionResponse,
+  NewSessionRequest,
+  NewSessionResponse,
+  PromptRequest,
+  PromptResponse,
+} from "@zed-industries/agent-client-protocol"
+import { Log } from "../util/log"
+import { ACPSessionManager } from "./session"
+import type { ACPConfig } from "./types"
+import { Provider } from "../provider/provider"
+import { SessionPrompt } from "../session/prompt"
+import { Identifier } from "../id/id"
+
+export class OpenCodeAgent implements Agent {
+  private log = Log.create({ service: "acp-agent" })
+  private sessionManager = new ACPSessionManager()
+  private connection: AgentSideConnection
+  private config: ACPConfig
+
+  constructor(connection: AgentSideConnection, config: ACPConfig = {}) {
+    this.connection = connection
+    this.config = config
+  }
+
+  async initialize(params: InitializeRequest): Promise<InitializeResponse> {
+    this.log.info("initialize", { protocolVersion: params.protocolVersion })
+
+    return {
+      protocolVersion: 1,
+      agentCapabilities: {
+        loadSession: false,
+      },
+      _meta: {
+        opencode: {
+          version: await import("../installation").then((m) => m.Installation.VERSION),
+        },
+      },
+    }
+  }
+
+  async authenticate(params: AuthenticateRequest): Promise<void | AuthenticateResponse> {
+    this.log.info("authenticate", { methodId: params.methodId })
+    throw new Error("Authentication not yet implemented")
+  }
+
+  async newSession(params: NewSessionRequest): Promise<NewSessionResponse> {
+    this.log.info("newSession", { cwd: params.cwd, mcpServers: params.mcpServers.length })
+
+    const session = await this.sessionManager.create(params.cwd, params.mcpServers)
+
+    return {
+      sessionId: session.id,
+      _meta: {},
+    }
+  }
+
+  async loadSession(params: LoadSessionRequest): Promise<LoadSessionResponse> {
+    this.log.info("loadSession", { sessionId: params.sessionId, cwd: params.cwd })
+
+    await this.sessionManager.load(params.sessionId, params.cwd, params.mcpServers)
+
+    return {
+      _meta: {},
+    }
+  }
+
+  async prompt(params: PromptRequest): Promise<PromptResponse> {
+    this.log.info("prompt", {
+      sessionId: params.sessionId,
+      promptLength: params.prompt.length,
+    })
+
+    const acpSession = this.sessionManager.get(params.sessionId)
+    if (!acpSession) {
+      throw new Error(`Session not found: ${params.sessionId}`)
+    }
+
+    const model = this.config.defaultModel || (await Provider.defaultModel())
+
+    const parts = params.prompt.map((content) => {
+      if (content.type === "text") {
+        return {
+          type: "text" as const,
+          text: content.text,
+        }
+      }
+      if (content.type === "resource") {
+        const resource = content.resource
+        let text = ""
+        if ("text" in resource && typeof resource.text === "string") {
+          text = resource.text
+        }
+        return {
+          type: "text" as const,
+          text,
+        }
+      }
+      return {
+        type: "text" as const,
+        text: JSON.stringify(content),
+      }
+    })
+
+    await SessionPrompt.prompt({
+      sessionID: acpSession.openCodeSessionId,
+      messageID: Identifier.ascending("message"),
+      model: {
+        providerID: model.providerID,
+        modelID: model.modelID,
+      },
+      parts,
+      acpConnection: {
+        connection: this.connection,
+        sessionId: params.sessionId,
+      },
+    })
+
+    this.log.debug("prompt response completed")
+
+    // Streaming notifications are now handled during prompt execution
+    // No need to send final text chunk here
+
+    return {
+      stopReason: "end_turn",
+      _meta: {},
+    }
+  }
+
+  async cancel(params: CancelNotification): Promise<void> {
+    this.log.info("cancel", { sessionId: params.sessionId })
+  }
+}