ACP Zed integration: mode switching and session management not working

[Mingholy]

ACP Zed Integration Issues

Problem Summary

When integrating Qwen Code with Zed editor (via ACP protocol), several incompatibilities with @zed-industries/claude-agent-acp's protocol format were discovered, causing the following features to malfunction:

1. Unable to switch Mode (plan/yolo/auto-edit etc.)
2. Session list display issues
3. Session resume functionality not working

Root Causes

Our ACP implementation had the following differences from @zed-industries/claude-agent-acp's protocol format:

1. session/new Response Missing Critical Fields

@zed-industries/claude-agent-acp (expected format):

{
  "sessionId": "xxx",
  "models": { ... },
  "modes": {
    "currentModeId": "default",
    "availableModes": [...]
  },
  "configOptions": [
    {
      "id": "mode",
      "name": "Mode",
      "type": "select",
      "currentValue": "default",
      "options": [...]
    },
    {
      "id": "model",
      "name": "Model",
      "type": "select",
      "currentValue": "default",
      "options": [...]
    }
  ]
}

Qwen Code (actual format):

{
  "sessionId": "xxx",
  "models": { ... }
  // Missing modes and configOptions
}

Impact: Zed client uses configOptions to render Mode/Model switching UI. Without these fields, users cannot switch modes.

---

2. session/list Response Format Mismatch

@zed-industries/claude-agent-acp (expected format):

{
  "sessions": [
    {
      "sessionId": "...",
      "cwd": "...",
      "title": "(session)",
      "updatedAt": "2026-02-28T02:34:57.639Z"
    }
  ]
}

Qwen Code (actual format):

{
  "items": [...],
  "hasMore": false,
  "nextCursor": 20
}

Issues:

• Field name mismatch: items should be sessions
• Missing fields: title, updatedAt
• Extra fields: hasMore, nextCursor

Additional issue: listSessionsRequestSchema had cwd as required, but Zed sends empty params {}.

Error message:

{
  "code": -32602,
  "message": "Invalid params",
  "data": {
    "details": "{\"_errors\": [], \"cwd\": {\"_errors\": [\"Required\"]}}"
  }
}

---

3. initialize Response Missing sessionCapabilities

@zed-industries/claude-agent-acp (expected format):

{
  "agentCapabilities": {
    "loadSession": true,
    "promptCapabilities": { ... },
    "sessionCapabilities": {
      "fork": {},
      "list": {},
      "resume": {}
    }
  }
}

Qwen Code (actual format):

{
  "agentCapabilities": {
    "loadSession": true,
    "promptCapabilities": { ... }
    // Missing sessionCapabilities
  }
}

Impact: Zed client cannot discover session list/resume capabilities.

---

Affected Files

• packages/cli/src/acp-integration/schema.ts
• packages/cli/src/acp-integration/acpAgent.ts

Recommendations

1. Reference Implementation: Consider referencing @zed-industries/claude-agent-acp's ACP implementation to ensure format compatibility.

2. Test Coverage: Add ACP protocol compatibility tests that compare our responses against @zed-industries/claude-agent-acp's responses.

3. Documentation: Update ACP integration documentation to describe supported features and known limitations.