Summary

In ACP mode (copilot-language-server --acp), session management requests fail with -32000 Authentication required when the user is not signed in. This applies even to session/list, which only reads local history. The Copilot CLI that the language server proxies to (copilot --acp) answers the same session/list without sign-in. So do the other ACP agents we tested.

Please let the session requests that read only local data work without authentication, at least session/list (and session/load / resume of an existing local session if possible). Keep authentication for requests that need the service, such as session/new and session/prompt.

Why it matters

ACP clients (IDEs) show a list of the user's previous agent sessions per project, so the user can find and reopen one. This list comes from local data. With the language server, a signed-out user sees an empty or failed list, although their sessions are on disk. Under ACP, an agent may answer any request with auth_required. Here the check sits in the proxy, not in the CLI that owns the data.

Steps to reproduce

1. Use a clean HOME with existing Copilot CLI sessions in ~/.copilot/session-state and no GitHub sign-in.
2. Start copilot-language-server --acp --stdio (1.552.0).
3. Send initialize, then session/list with a cwd that has sessions.

Actual: {"code": -32000, "message": "Authentication required"}. Also, offline, initialize takes about 25 s.

Expected: the local sessions, as copilot --acp returns them.

Comparison: session/list without sign-in (Linux container, isolated HOME, synthetic history)

Environment

• @github/copilot-language-server 1.552.0 and @github/copilot 1.0.95.
• Node 24, Debian bookworm (Docker). The behaviour does not depend on the OS.
• Client: an ACP client (JetBrains Air) that sends initialize and then session/list.