[FEATURE]: Add TUI session navigation mode

[samiralibabic]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

OpenCode has scroll keybinds, but there is no focused keyboard navigation mode for paging through long session output with Vim-style bare keys without changing prompt editing.

This requests a small session navigation mode:

• Escape enters navigation mode when the prompt/session is idle
• j/k and page keys scroll output
• gg/G jump to start/end
• n/N/p jump between user messages
• i/a/Enter exits and restores prompt focus

This keeps normal prompt text entry unchanged. Bare letters still type normally while the prompt is focused; bare Vim-style navigation keys only apply while the session is in NAV mode.

Related issues like #2755 and #1764 discuss broader Vim/keybinding needs. This request is intentionally narrower: keyboard-first navigation of existing session output without adding modal prompt editing.

[github-actions]

This issue doesn't fully meet our contributing guidelines.

What needs to be fixed:

• Feature requests must use the Feature Request issue template: the title should start with [FEATURE]:, include the required verification checkbox, and use the structured description fields.

Please edit this issue to address the above within 2 hours, or it will be automatically closed.

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This issue might be a duplicate of existing issues. Please check:

• feat: Copy Mode for OpenCode #2755: Copy Mode for OpenCode — proposes vim/tmux-like keyboard navigation (j/k, page keys) through session output, which overlaps significantly with this request.
• [FEATURE]: vim motions in input box #1764: [FEATURE]: vim motions in input box — related vim-keybind navigation in the TUI.

For keybind-related issues, please also check our pinned keybinds documentation: #4997

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

Thanks for updating the issue! It now follows the contributing guidelines and the needs:compliance label has been removed. Your feature request looks good — the description is clear and focused. We appreciate you taking the time to fix it.

[kommander]

We are working on better built-in session navigation. Meanwhile, this can be built as tui plugin using the keymap and everythiong else exposed to plugins.

[rentiansheng]

back to bottom is quite necessary. I added one myself. After reviewing history, it's quite slow to catch up on the latest content.