Prompt suggestions: pre-fill a suggested next prompt in the message box after the agent replies #5035

Feature summary

After the agent replies, show a suggested next prompt as ghost text in the message box that I can accept with one key or ignore by typing.

What problem are you trying to solve?

When an agent finishes a turn, the next step is usually obvious: commit the change, open a PR, run the tests, apply the fix it just diagnosed. Right now I have to type that out every time and have gotten used to other harnesses having that capability. Coming back to Copilot makes me realize how much I use that feature.

Proposed solution

When the agent finishes replying, predict the prompt I'm most likely to send next and show it as placeholder/ghost text in the message box.

• Tab (or →) accepts it into the input so I can send as-is or edit it first; Enter on an empty box could send it directly.

• Typing anything replaces it, so it never gets in the way.

• Suggestions are short and concrete, based on the conversation: "commit these changes", "run the tests again", "open a PR", "now apply the same fix to the other handler".

• Only one suggestion, and none when there's no obvious next step.

• Opt-in setting, since generating the suggestion costs a bit of extra usage/premium requests. Something like:

  Prompt suggestions
  Show a suggested next prompt in the message box after the agent replies. Suggestions add a little to your usage.

Claude Code (CLI and desktop app) ships exactly this behind a "Prompt suggestions" setting.

Workflow impact

Anyone chatting with agents in the app, especially in long iterative sessions.

• Most follow-ups are short and predictable; accepting one with Tab is faster than typing it.
• Keeps momentum when bouncing between several sessions, since the likely next step is already sitting in the box.
• Zero cost to people who don't want it: off by default, and ignored the moment you start typing.

Installation context

No response

Additional context

Reference: Claude Code's "Prompt suggestions" setting ("Show a suggested next prompt in the message box after Claude replies. Suggestions add a little to your usage.").