Up/Down arrow keys no longer navigate prompt history #15761

Description

Since commit 3dc10a1 ("Change keybindings to navigate between child sessions"), pressing Up/Down arrow keys no longer navigates through prompt history in the TUI.

The commit changed session_parent default keybind from <leader>up to bare up, which now conflicts with history_previous also bound to up. The session_parent command is matched first in the command dialog's useKeyboard handler, which calls evt.preventDefault() before onSelect. When there is no parent session, onSelect silently returns — but the event is already consumed, so it never reaches the textarea's onKeyDown where history navigation lives.

Steps to reproduce

1. Open opencode TUI
2. Send a message
3. Press Up arrow to recall previous prompt
4. Nothing happens — the arrow key is swallowed by the no-op session_parent command

Operating System

Linux (Ubuntu)

Terminal

Ghostty