Agent view: allow switching sessions while input has text (preserve draft)

Problem

In agent view, when text is typed into the dispatch input at the bottom, the ↑ / ↓ arrow keys navigate within the text rather than moving between session rows. There's no documented modifier-key combo to switch sessions while preserving what you've typed.

The current options are both lossy or limited:

• Esc clears the input and restores arrow-key navigation — but you lose the draft.
• Alt+1..Alt+9 jumps directly to a session — but only works for the first nine sessions, and requires knowing the position. Doesn't scale once you have more than nine, and isn't great for sequential browsing.

Suggested behavior

Add a modifier-based shortcut that navigates between session rows even when the dispatch input has focus and contains text. Reasonable candidates:

• Ctrl+↑ / Ctrl+↓ (or Cmd+↑ / Cmd+↓ on macOS)
• Alt+↑ / Alt+↓
• Shift+Tab / Tab

Whichever is least likely to conflict with existing terminal/input bindings. The key behavior is: navigate sessions without clearing the draft, so users can compose a prompt, glance at another session's output for context, and return to finish typing.

Why it matters

A common flow is "I'm writing a dispatch prompt and I want to peek at what another running agent just produced before I finalize the wording." Today that flow forces a choice between losing the draft (Esc) or memorizing session numbers (Alt+N). A modifier-arrow shortcut would make agent view feel a lot more like a real multi-session workspace.

Environment

• Reported via Claude Code on macOS (Darwin 25.4.0), zsh.