fix(tui): don't show 'Agent not found' toast for subagents

[vtemian]

Summary

When a command runs with a subagent (e.g., /init with project-initializer), the TUI incorrectly shows an "Agent not found" toast error.

Related issues

#6518

Root Cause

The code added in #6325 (variants toggle) syncs the agent from the last user message to the TUI:

if(msg.agent)local.agent.set(msg.agent)

However, local.agent.list() only includes primary agents (mode !== 'subagent'), so when a command runs with a subagent, the set() call fails and shows the toast.

The backend correctly creates and runs the subagent session - only the TUI display has this bug.

Fix

Check if the agent exists in the primary agents list before attempting to set it:

if(msg.agent&&local.agent.list().some((x)=>x.name===msg.agent))local.agent.set(msg.agent)

Testing

1. Create a custom command that uses a subagent (e.g., /init with agent: "my-subagent")
2. Run the command
3. Before: "Agent not found: my-subagent" toast appears
4. After: No toast, command runs correctly