feat(tui): add raw scrollback mode

[fcoury-oai]

Why

Granular copy is particularly difficult with the current output. Part of it was solved with the introduction of the /copy command but when you only need to copy parts of a response, you still encounter some issues:

• When you copy a paragraph, the result is a sequence of separate lines instead of one correctly joined paragraph.
• When a word wraps, part of it stays on the original line and the rest appears at the start of the next line.
• When you copy a long command, extra line breaks are often inserted, and command arguments can be split across multiple lines.

rawmode_75.mp4

Solution

Now that we own the scrollback and we re-create it when we resize, we have the opportunity of toggling between the raw text and the rich text we see today.

• Add TUI raw scrollback mode with tui.raw_output_mode, /raw [on|off], and the configurable tui.keymap.global.toggle_raw_output action.
• Render transcript cells through rich/raw-aware paths so raw mode preserves source text and lets the terminal soft-wrap selection-friendly output.
• Bind raw-mode toggle to alt-r by default, with the keybinding path toggling silently while /raw continues to emit confirmation messages.

Related Issues

Likely addressed by raw mode:

• Clean Copy for Multiline and Soft-Wrapped Output #12200: clean copy for multiline and soft-wrapped output. Raw mode removes Codex-inserted wrapping/indentation and lets the terminal soft-wrap logical lines.
• Remove 2 leading spaces from cmd suggestion #9252: command suggestions gain unwanted leading spaces when copied. Raw mode renders transcript text without the rich-mode left padding/gutter.
• [FEATURE] Remove leading two-space indent from prompts #8258: prompt output is hard to copy because of leading indentation. Raw mode renders user/source-backed transcript text without that decorative indentation.

Partially or conditionally addressed:

• Copy/Export Message as Markdown #2880: copy/export message as Markdown. Raw mode exposes raw Markdown for terminal selection, but this PR does not add a dedicated export/copy-message command.
• Mouse drag selection + copy in the TUI #19820: mouse drag selection + copy in the TUI. Raw mode improves terminal-native selection of output/history text, but this PR does not implement in-TUI mouse selection, highlighting, auto-copy, or composer selection.
• Copy a piece of content to the CLI, and it is divided into two parts. #18979: copied content is divided into two parts. This should improve cases caused by Codex-inserted wraps/padding in rendered output; if the report is about pasting into the composer/input path, that remains outside this PR.

Validation

• just write-config-schema
• just fmt
• cargo test -p codex-config
• cargo test -p codex-tui
• just fix -p codex-tui
• just argument-comment-lint
• cargo test -p codex-tui raw_output_mode_can_change_without_inserting_notice -- --nocapture
• cargo test -p codex-tui raw_slash_command_toggles_and_accepts_on_off_args -- --nocapture
• cargo test -p codex-tui raw_output_toggle -- --nocapture
• git diff --check
• cargo insta pending-snapshots

[canvrno-oai]

Tested raw scrollback mode by toggling it on and off during streaming, resizing the terminal including narrow widths, and viewing markdown-heavy output with lists and paragraphs.