ACP session/new always returns -32603 Internal error

[haoxuhong]

Description

Problem

When using OpenCode via ACP (Agent Client Protocol), the initialize handshake succeeds, but session/new always returns -32603 Internal error.

Environment

• OpenCode version: 1.14.33 (npm) and 1.14.29 (registry)
• OS: macOS 26.3 (darwin arm64)
• Node: v23.11.0
• IDE: Android Studio Panda 4 | 2025.3.4
• AI Assistant plugin: 253.32098.66

Reproduction

Command line repro:

(echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":1,"clientCapabilities":{"fs":{"readTextFile":true,"writeTextFile":true}},"clientInfo":{"name":"test","version":"0.1.0"}}}'; sleep 1; echo '{"jsonrpc":"2.0","id":2,"method":"session/new","params":{"cwd":"/Users/haoxuhong","mcpServers":[]}}'; sleep 3) | opencode acp 2>&1

Output

{"jsonrpc":"2.0","id":1,"result":{"protocolVersion":1,...}}  <-- initialize OK
Error handling request { jsonrpc: "2.0", id: 2, method: "session/new", params: { cwd: "/Users/haoxuhong", mcpServers: [] } } { code: -32603, message: "Internal error", data: {} }
{"jsonrpc":"2.0","id":2,"error":{"code":-32603,"message":"Internal error","data":{}}}  <-- session/new FAILS

The error occurs regardless of the cwd value. Tested with home directory and multiple project directories.

Also tested with the Registry-installed version (1.14.29) via Android Studio AI Assistant plugin (253.32098.66) with identical results.

ACP Transport Log

OUT: {"method":"initialize",...}  <-- sent
IN:  {"id":1,"result":{...}}      <-- success
OUT: {"method":"session/new","params":{"cwd":"...","mcpServers":[]}}
IN:  {"id":2,"error":{"code":-32603,"message":"Internal error"}}  <-- fails

Additional Context

• OpenCode was installed via npm install -g opencode-ai
• Credentials are configured (OpenCode Zen, Z.AI Coding Plan, Z.AI)
• The same issue occurs both with manual acp.json configuration and with Registry-installed agent
• ACP initialize succeeds and returns correct capabilities, but any subsequent session/new fails

Plugins

No response

OpenCode version

No response

Steps to reproduce

No response

Screenshot and/or share link

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Operating System

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Terminal

No response

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• session/new returns "Internal error" on Windows via ACP #17285: session/new returns "Internal error" on Windows via ACP — same symptom (initialize succeeds, session/new fails with -32603 Internal error) via ACP protocol