OpenCode ACP Missing Methods - Breaks Claudian Integration

[dspetrich]

Description

Environment
OpenCode version: 1.14.29
macOS (Apple Silicon)
Claudian Obsidian plugin v2.0.8
Issue
OpenCode's ACP (Agent Client Protocol) implementation is missing critical methods that prevent third-party integrations (like Claudian) from working.
Missing Methods

1. newSession - Method Not Found
   echo '{"jsonrpc":"2.0","id":2,"method":"newSession","params":{}}' | opencode acp
   Returns:
   {"jsonrpc":"2.0","id":2,"error":{"code":-32601,"message":""Method not found": newSession"}}
   Expected: Should create a new session and return sessionId
   Actual: Method not found error
2. authenticate - Not Implemented
   echo '{"jsonrpc":"2.0","id":2,"method":"authenticate","params":{"methodId":"opencode-login"}}' | opencode acp
   Returns:
   {"jsonrpc":"2.0","id":2,"error":{"code":-32603,"message":"Internal error","data":{"details":"Authentication not implemented"}}}
   Expected: Should handle authentication flow
   Actual: "Authentication not implemented" error
   Impact
   Without these methods, ACP clients like Claudian cannot:
   Create new sessions (must pre-create via TUI)
   Authenticate programmatically (shows "authentication_failed" errors)
   Discover available models (requires active session)
   Workaround
   None currently available. Users must use Claude Code or Codex providers instead.
   Related
   The initialize response advertises authMethods with opencode-login, but calling authenticate returns "not implemented". This is misleading.
   Capabilities response shows:
   {
   "loadSession": true,
   "sessionCapabilities": {"fork": {}, "list": {}, "resume": {}}
   }
   Note the absence of newSession capability, which Claudian expects.
   Request
   Please implement:
   newSession method to create sessions via ACP
   authenticate method or remove it from advertised authMethods
   Add newSession to advertised capabilities if/when implemented

Plugins

No response

OpenCode version

1.14.29

Steps to reproduce

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Screenshot and/or share link

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Operating System

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Terminal

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