Composer placeholder: cannot disable + suggestions are not task-aware

Summary

Two UX issues around the composer placeholder text in Codex CLI:

1. There is currently no public config to disable the input-box placeholder text.
2. The placeholder suggestions are often unrelated to the current task context or recent task history.

Environment

• Codex CLI version: 0.107.0
• OS: macOS (Apple Silicon)
• Config file: ~/.codex/config.toml (symlinked to dotfiles)

What I already tried

I configured:

[tui]
show_tooltips = false

This works for welcome tooltips, but does not affect the composer/input placeholder (e.g. Write tests for @filename).

Steps to reproduce

1. Set show_tooltips = false under [tui] in ~/.codex/config.toml.
2. Restart Codex CLI.
3. Observe the input box when idle.

Actual behavior

• Placeholder text still appears in the input box.
• Placeholder examples can be unrelated to the active session goals.

Expected behavior

• A config option to disable input placeholder entirely (for distraction-free mode), e.g. tui.show_input_placeholder = false.
• If enabled, placeholder suggestions should be context-aware (current task / recent interactions), not generic or unrelated.

Why this matters

For users who prefer a minimal UI, static/generic placeholder hints add noise and can conflict with task focus.