Feature Request: Add unstable session capabilities (sessionCapabilities.resume/fork/list)

[toontimbermont]

Hi! 👋

First off, thank you for maintaining this SDK - it's been really helpful for building Go-based ACP clients.

Context

I'm building a chat workbench that integrates with Claude Code via ACP. I've been investigating how the Obsidian Agent Client plugin (using TypeScript SDK v0.12.0) successfully restores conversation context across sessions.

What I discovered

Through testing, I confirmed that Claude Code ACP reports loadSession: false and returns "Method not found": session/load when called:

AgentCapabilities.LoadSession: false
Error: {"code":-32601,"message":"\"Method not found\": session/load","data":{"method":"session/load"}}

However, the Obsidian plugin still achieves session restoration. Looking at their code, they check for unstable session capabilities:

// From session-capability-utils.ts
canLoad: agentCapabilities?.loadSession === true,
canResume: agentCapabilities?.sessionCapabilities?.resume !== undefined,
canFork: agentCapabilities?.sessionCapabilities?.fork !== undefined,
canList: agentCapabilities?.sessionCapabilities?.list !== undefined,

And use methods like:

• connection.unstable_resumeSession({ sessionId, cwd })
• connection.unstable_forkSession({ sessionId, cwd })
• connection.unstable_listSessions({ cwd, cursor })

The gap in Go SDK v0.6.3

The Go SDK has:

• ✅ LoadSession() method
• ✅ AgentCapabilities.LoadSession field

But is missing:

• ❌ AgentCapabilities.SessionCapabilities struct with Resume, Fork, List fields
• ❌ UnstableResumeSession() method
• ❌ UnstableForkSession() method
• ❌ UnstableListSessions() method

Request

Would you consider adding these unstable session capabilities for parity with the TypeScript SDK? Specifically:

1. Types - Add to AgentCapabilities:

   type SessionCapabilities struct {
       Resume *ResumeCapability `json:"resume,omitempty"`
       Fork   *ForkCapability   `json:"fork,omitempty"` 
       List   *ListCapability   `json:"list,omitempty"`
   }
   
   type AgentCapabilities struct {
       // ... existing fields
       SessionCapabilities *SessionCapabilities `json:"sessionCapabilities,omitempty"`
   }

2. Client methods:

   • UnstableResumeSession(ctx, params) (ResumeSessionResponse, error)
   • UnstableForkSession(ctx, params) (ForkSessionResponse, error)
   • UnstableListSessions(ctx, params) (ListSessionsResponse, error)

Use case

This would enable Go clients to:

• Restore previous chat sessions with full AI context
• Show users a list of their previous conversations
• Fork conversations to explore different paths

References

• Obsidian plugin's acp.adapter.ts - shows usage patterns
• Obsidian plugin's useSessionHistory.ts - shows capability detection
• TypeScript SDK @agentclientprotocol/sdk v0.12.0

Happy to help with implementation or testing if that would be useful!

[ThomasK33]

Hey @toontimbermont, thanks for opening the issue.

Can you give this branch/PR a try and see if it works for you? #17

[agentcooper]

I did this in my fork (agentcooper#3).

@ThomasK33 PR #17 adds those methods, but I had to update the code generator to get related fields inside SessionCapabilities.