`session/new` fails with Internal error when called immediately after `initialize` in ACP stdio mode

[yudaiyan]

Bug: session/new fails with Internal error when called immediately after initialize in ACP stdio mode

Description

When using OpenCode as an ACP (Agent Client Protocol) agent via stdio, the session/new method fails with "Internal error" (code -32603) if called immediately after initialize returns.

Steps to Reproduce

# Using acpx (ACP client)
npx acpx opencode exec "your task"

# Or using direct stdio
(echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":1,"clientCapabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}'; sleep 0.1; echo '{"jsonrpc":"2.0","id":2,"method":"session/new","params":{"cwd":"/tmp","mcpServers":[]}}') | opencode acp

Expected Behavior

session/new should succeed after initialize returns successfully.

Actual Behavior

{"jsonrpc":"2.0","id":2,"error":{"code":-32603,"message":"Internal error","data":{}}}

Root Cause Analysis

From the logs, OpenCode's initialize response is sent before internal initialization is fully complete. The server needs additional time (~2 seconds) to:

1. Load user configuration
2. Initialize providers
3. Set up the default model

When session/new arrives during this initialization window, it fails because the required services aren't ready yet.

Workaround

Adding a 2-second delay between initialize response and session/new request resolves the issue:

// In acpx client
await connection.initialize({...});
await new Promise(resolve => setTimeout(resolve, 2000)); // workaround
await connection.newSession({...});

Testing Results

Delay after initialize	Result
100ms - 1500ms	❌ Internal error
2000ms+	✅ Success

Environment

• OpenCode version: 1.4.0
• Node version: 24.14.0
• OS: Linux (WSL2)
• Config: model: "bailian-coding-plan/glm-5" with custom providers

Suggested Fix

One of these approaches would resolve the issue:

1. Delay the initialize response until all internal initialization is complete
2. Queue early requests and process them after initialization finishes
3. Return a specific error code (not generic Internal error) to help clients implement retry logic

Related

• acpx workaround commit: https://github.com/sstur/acpx (if applicable)

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This issue affects any ACP client that follows the standard protocol flow of calling initialize then immediately calling session/new. The current behavior breaks ACP compatibility.