SessionStart hook waiting reworked across queued prompts and messages

What

• The core per-turn input processor now waits for any pending SessionStart hooks to finish before a queued prompt (or a non-prompt-type slash command) is sent to the model, handling cancellation and re-queueing if that wait is interrupted.
• When draining the command queue for a resurrected session, if every currently queued exempt command came from that resurrection, execution now waits for SessionStart hooks to resolve before running the queue, instead of executing immediately.
• In the host's reply/message-launch flow, a previous wait for pending hooks before deciding how to send an outgoing queued message (direct insert, enqueue, or immediate run) was removed from that path.

Why

This ensures prompts and resurrected-session commands aren't sent to the model until session-start setup has actually finished, while removing a redundant wait in the separate host message-dispatch path.