Agent Host: runtime slash commands (e.g. /chronicle) don't autocomplete in the new-session composer

[digitarald]

Problem

In an Agent Host Copilot (copilotcli) session, runtime slash commands do not autocomplete in the new-session composer (the "New session in … with Copilot" input, before a session has been created). Typing /chro there shows no /chronicle suggestion. Once the session is live (after the first message / session creation), the same input correctly autocompletes /chronicle and other runtime commands.

This is not specific to /chronicle — no runtime slash command appears in the pre-creation composer, because runtime commands are only discoverable through a live SDK session.

Steps to Reproduce

1. Start the Agent Host (node ./scripts/code-agent-host.js).
2. Open the new-session composer ("New session in with Copilot"), provider = Copilot.
3. Type /chro (or just /).
4. Observe: no runtime slash-command completions (/chronicle, etc.). Only completions that don't require a live session (skills/files) may appear.
5. Create/start the session (send a first message), then type /chro again.
6. Observe: /chronicle (and its subcommand options) now autocompletes.

[DonJayamanne]

Duplicate of #323565