A session created with create_session can't be resumed after close_session if the user had switched to it #5386

Describe the bug

A session made with create_session, which the user has switched to and which another session then closes with close_session, can't be reopened in the same CLI process. /resume fails with:

Failed to switch session: Error: Failed to associate local session <id> with its built-in plugin host

Relaunching the CLI, or opening the session from a new CLI process, lets it reopen normally.

A created session that the user never switched to reopens normally after the same close. After the failed attempt, at a later switch between sessions, the CLI starts an MCP server process for the session that didn't open and leaves it running.

Affected version

GitHub Copilot CLI 1.0.108-1

Steps to reproduce the behavior

1. Turn on session management tools (sessionManagementTools in ~/.copilot/settings.json). Our setup also had user extensions and one remote MCP server; we haven't tried without them.
2. In session A, call create_session twice to make sessions B and C.
3. Switch to B, then back to A. Don't switch to C.
4. In A, call close_session for B and for C.
5. Run /resume and pick B. It fails with the error above.
6. Run /resume and pick C. It opens.

When A closes B, the log shows Cleaning up session <B>: Session closed via sessions.close, then Failed to apply session management settings: Error: the Copilot SDK reported a failure: RPC error -32603: Request session.management.configure failed with message: The destination session is not available. Closing C logs only Closing session <C>.

Expected behavior

A session closed with close_session can be reopened with /resume whether or not the user had switched to it.

Additional context

• macOS on Apple silicon (arm64).
• Seen twice on 2026-11-08 with different sessions. Both times an MCP server process for the session that failed to reopen was still running afterward.
• Related: Extensions don't start for sessions created with create_session until the user switches to them #5380 (created sessions start extensions only when the user switches to them) and Switching sessions in the Sessions sidebar leaks plugin MCP servers and extension hosts (OOM) #5164 (switching sessions leaks MCP servers and extension hosts).