[FEATURE] Persist argument-hint outside the input box while typing arguments

Problem

The argument-hint from slash command / skill frontmatter is shown inline next to the command name, but disappears the moment you start typing arguments. For commands with multiple positional or named args, you have to remember the entire signature mid-flow — and if you forget, the only way to peek again is to delete what you've typed or restart the command.

This gets noticeably worse for skills with 3+ arguments or key="a|b|c" shaped hints, where the hint itself is the documentation.

#20667 raised the same underlying complaint ("hint disappears while typing") and was auto-closed as a duplicate of #20234, but #20234 is actually about autocompleting argument values — a different feature. So the persistence problem is currently unaddressed.

Proposed solution

Keep the argument hint visible somewhere outside the chat input while the user is typing arguments. A few possible placements:

• A thin status row directly above (or below) the input box, persistently rendering the hint
• A floating tooltip-like strip anchored to the input, like IDE parameter info
• An inline strip that doesn't compete with the user's typed text for the same line

Bonus: highlight/bold the current argument position as the user types past each separator (space / =), so multi-arg hints stay legible.

<img width="853" height="46" alt="Image" src="https://github.com/user-attachments/assets/eea175e8-684e-4aa4-bc95-d1acea4f00a8" />

Alternatives considered

• Keep the hint inline but dimmed — was the original ask in #20667; closed before being acted on.
• Argument value autocomplete — covered by #20234 and #56918, doesn't help when you just want to see the signature.
• Mid-input slash command hint support — covered by #42147, orthogonal.
• Workaround today: delete typed args to redisplay the hint, or keep the SKILL.md open in another window. Both are bad.

Priority

Medium

Category

Interactive mode (TUI)