## Why
Session transitions need stack headroom for embedded-server initialization and configuration loading. Running them inside event dispatch risks exhausting the TUI thread's stack.
## What changed
- Queue `/resume` and valid `/cd` requests for processing after event dispatch returns.
- Reject additional `/cd` requests while one is pending, and recheck the source session, working directory, idle state, and remote-environment restrictions before applying it.
## Testing
Add a Unix PTY regression test that exercises `/resume`, worktree conversation forks, `/cd`, and new worktree conversations through the real TUI event loop. Update the directory-change test to verify that dispatch queues the request without immediately changing configuration.
GitOrigin-RevId: 4950921931dfaba9e55e6bb04f98f7ba64b72122
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