Ctrl+V in TUI is image-only when it reaches Codex as a key event; add symmetric text paste

[dolzenko]

Summary

In the TUI, Ctrl+V currently behaves as an image-paste shortcut if it reaches Codex as a key event.

That means when the clipboard contains text, and the terminal does not convert the paste into a bracketed Paste(...) event, Codex tries to
paste an image instead and shows an error like:

Failed to paste image: no image on clipboard: ...

Root cause

There are currently two different paste paths:

• text paste: relies on terminal/crossterm Event::Paste(...)
• Ctrl+V: handled as clipboard image paste in the TUI keybinding layer

So if the terminal forwards Ctrl+V as a keypress instead of surfacing a paste event, text paste does not happen inside Codex.

Proposed behavior

• Ctrl+V in local desktop sessions:
  • try clipboard text first
  • if non-empty text exists, route it through the existing composer paste path
  • if no text exists, fall back to image paste
• Alt+V:
  • remain explicit image paste
• SSH/remote sessions:
  • do not do process-local text clipboard reads
  • rely on terminal-owned paste
  • if Ctrl+V reaches Codex as a key event, show a short hint instead of reading the remote process clipboard

Why this shape

• preserves terminal-native Paste(...) handling
• preserves explicit image paste
• avoids incorrect clipboard semantics in SSH sessions
• makes Ctrl+V symmetric for local users whose terminal forwards the keypress

Local implementation + verification

I implemented this in a local clone and verified with:

• just fmt
• cargo clippy -p codex-tui --tests
• cargo test -p codex-tui

The change includes:

• text clipboard read helper
• WSL text fallback
• Ctrl+V text-first shortcut policy
• Alt+V image-only policy
• SSH hint path
• updated footer/snapshots/tests

If this approach matches the intended direction, I can turn it into a PR if invited.

[github-actions]

Potential duplicates detected. Please review them and close your issue if it is a duplicate.

• An error occurred when I copied text to the Codex CLI using the clipboard. #16223
• Clipboard paste prefers image over text when clipboard contains both #15436

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[dolzenko]

A little more context - #4818 (comment) I originally needed this for implementing cross-layout Ctrl-V paste with alacritty

#16223 is also very likely might be solved with this change.

[dolzenko]

a64505379 the changeset codex gave me