tui: expand image placeholders to full paths for models (keep basenames for users)

[mikita-oai]

What

• When a user pastes a local image file path (or pastes an image from the clipboard), the TUI inserts an attachment
  placeholder into the composed prompt. This placeholder now includes the full path (e.g. /tmp/image.png instead of only the basename (e.g. image.png).
• We separate the user-visible vs model-visible placeholder, to preserve the current aesthetics and avoid cluttering the input. So the user still sees image.png while the model sees /tmp/image.png.
• Updated both TUI implementations (codex-tui and codex-tui2) + tests.

Why

• Basename-only placeholders make it hard for the model to refer back to the actual local path (e.g. when the user wants
  the model to use the path in commands / docs / patches rather than “just see the image”).

Testing done

1. Updated automated tests and ran:

cargo test -p codex-tui; cargo test -p codex-tui2

2. Built codex locally and confirmed it can now see the full path

[github-actions]

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[Copilot]

Pull request overview

This PR updates the TUI attachment placeholder format to use full file paths instead of basenames, enabling models to reference the actual local file paths in responses.

Key Changes:

• Modified attach_image() in both TUI implementations to use path.display() instead of extracting the filename
• Updated all test assertions to expect full paths in placeholders (e.g., [/tmp/image.png 24x42] instead of [image.png 24x42])

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
codex-rs/tui2/src/bottom_pane/chat_composer.rs	Changed placeholder generation to use full path via path.display() instead of file_name()
codex-rs/tui2/src/chatwidget/tests.rs	Updated test assertion to expect full path in placeholder
codex-rs/tui/src/bottom_pane/chat_composer.rs	Changed placeholder generation to use full path via path.display() instead of file_name()
codex-rs/tui/src/chatwidget/tests.rs	Updated test assertion to expect full path in placeholder

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[mikita-oai]

I have read the CLA Document and I hereby sign the CLA