Claude ACP agent fails: all sessions end with 0 turns, agent disconnects after ~3s

[danyeoakl]

Environment

• acpx: 0.1.13
• @zed-industries/claude-agent-acp: 0.19.2
• @agentclientprotocol/sdk: 0.14.1 (both sides)
• @anthropic-ai/claude-agent-sdk: 0.2.62
• Claude Code CLI: 2.1.50
• Node: v24.13.1
• macOS (arm64)

Problem

Claude ACP sessions never complete a turn. Codex ACP works fine with the same acpx version.

Observed behavior

1. acpx claude sessions new → session created ✅
2. acpx claude prompt --session <name> --file - → agent needs reconnect → starting detached queue owner → [error] RUNTIME: Internal error
3. Session record shows: agentCapabilities: yes, protocolVersion: 1, but turns: 0, lastAgentDisconnectReason: connection_close
4. Queue owner process stays alive (heartbeating), but the Claude agent subprocess exits ~3 seconds after start
5. Claude debug logs show clean startup through ripgrep test — no errors logged
6. Direct claude --print works fine (auth is good)
7. Tested 13 sessions across multiple attempts — all show same pattern

Timeline from session record

• agentStartedAt: T+0s
• lastPromptAt: T+0.5s
• lastAgentExitAt: T+2.6s
• lastAgentExitCode: null
• lastAgentExitSignal: null
• lastAgentDisconnectReason: connection_close

Comparison with Codex (working)

• Codex sessions: 3/3 completed, 2 turns each
• Claude sessions: 13/13 failed, 0 turns each
• Both use @agentclientprotocol/sdk@0.14.1
• Both have agentCapabilities set (init handshake works)

Config

permissionMode: approve-all
nonInteractivePermissions: deny
authPolicy: skip

Likely cause

Something in the lifecycle between queue owner starting the claude agent subprocess and delivering the first prompt. The agent connects, exchanges capabilities, but then disconnects before any turn completes. The newSession or prompt RPC may not be reaching the agent correctly.