Better use of horizontal space in the session view on wide terminals #32995

Type: Feature request / discussion

Summary

On wide / fullscreen terminals, the session message area doesn't make good use of the available width. The effective content reads as a narrow band with large empty margins on the sides, so a lot of screen real estate is wasted.

What I found in the source

While looking at packages/tui/src/routes/session/index.tsx:

• layout ("auto" | "stretch") in the main config is @deprecated and now always uses stretch (see https://opencode.ai/config.json), so the column should already stretch to full width.
• The sidebar auto-shows when dimensions().width > 120 and consumes 42 columns (index.tsx:265, index.tsx:273):

  const wide = createMemo(() => dimensions().width > 120)
  const contentWidth = createMemo(() => dimensions().width - (sidebarVisible() ? 42 : 0) - 4)

• The message container is flexGrow={1} with paddingLeft/Right={2} (index.tsx:1168-1169), and individual messages have no maxWidth — they fill the available column.

So on a wide terminal the main levers left are the hardcoded 120 sidebar threshold and the 42-col sidebar width. Hiding the sidebar (session.sidebar.toggle) reclaims width, but the threshold itself isn't configurable, and on ultra-wide terminals full-width raw text is hard to read, so some users actually want an opt-in centered column.

Proposals (open for discussion)

1. Make the wide threshold (120) configurable via the TUI config (e.g. session.sidebar_width / session.wide_threshold), so users on smaller-but-wide terminals can keep messages wide.
2. Add an optional session.content_max_width (similar to the existing prompt.max_width on Home, config/index.tsx:48) so ultra-wide users can center a readable column, while narrow users keep full stretch.
3. Auto-hide the sidebar when showing it would push contentWidth below a minimum ratio.

Environment

• opencode: latest dev (cloned for source reading)
• Terminal: wide/fullscreen (please confirm your exact width + whether sidebar is visible when you see this)

Willing to contribute

Happy to open a PR once a direction is agreed. The change for proposal 1 is small (a couple of lines); proposal 2 is a bit more involved but still contained to routes/session.