Surface Claude Code's prompt suggestions in the composer

[goncharik]

Claude Code's SDK emits a predicted next prompt after each turn. T3 already receives it and throws it away:

// apps/server/src/provider/Layers/ClaudeAdapter.ts:3642
// Composer prompt suggestions have no T3 surface; consumed deliberately.
case "prompt_suggestion":
  return;

That line came from 6f34ad3e8 (#4244), which enumerated every SDK message type to satisfy the message satisfies never guard. It reads like a placeholder, not a decision against the feature.

I built it on a fork to find out what it actually costs. Posting here instead of opening a PR because CONTRIBUTING.md routes proposals to Ideas and says to discuss non-trivial changes first.

What it does

Web/desktop: dim ghost placeholder text in the empty composer. Tab accepts, Esc dismisses. Shift+Tab still toggles plan mode, and Tab still reaches the mention/slash menu when that popover is open.

Mobile: a dismissible chip above the input. Tap accepts, X dismisses.

Claude-only. The other adapters never emit the event, the shell field stays null, nothing renders. No per-adapter work.

Design

The value lives in an in-memory ThreadPromptSuggestion service, matching ThreadPlanProgress and ThreadBackgroundLiveness — no migration, no column, empty after restart. A minimal persisted event exists only to trigger the shell refetch, because ws.ts only pushes off persisted thread-aggregate events and the suggestion arrives after turn.completed, so nothing else follows it.

Cleared on turn.started and session.exited, never on turn completion. Clearing on completion wipes the suggestion the moment it lands.

The suggestion is stamped with the completed turn id, and ingestion drops it if a different turn is already running by the time it arrives. The CLI generates it in a fire-and-forget background query, so it can land after the user has already sent the next prompt.

Size

35 files, +2118/-95. Roughly half is tests and docs. That is past what CONTRIBUTING.md says you want, which is the other reason this is a discussion and not a PR.

Branch: https://github.com/goncharik/t3code/tree/claude-prompt-suggestions

Caveats

Always on, no T3 setting. The only off switch is CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION=false. I disassembled the CLI to check: promptSuggestionEnabled in settings.json gates the interactive REPL's own ghost text, not the SDK stream. The emit site is gated on C.promptSuggestions && ot.shouldQuery!==false && !Vi() && a.CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION!==false — the settings key is not consulted. Adding a ClaudeSettings toggle is contained if you'd want one.

While ghost text is showing, Tab is consumed to accept it, so you can't tab out of an empty composer without dismissing first. Matches other ghost-text editors, but it is a behavior change.

Suppressed on the first turn, in plan mode, and after API errors. Absence is the normal case, which the docs say explicitly so it doesn't read as a bug.

Screenshots for web/desktop, Android, and iOS in a comment below.

Happy to shrink it, split it, or drop it.

[goncharik]

Web / desktop — ghost placeholder text, Tab to accept

Mobile — dismissible chip above the input, tap to accept, X to dismiss

Android	iOS

[orowebregen]

This would be very helpful. I wish this existed.

[thedrowsywinger]

Linking #8524, which was closed with two concerns: durable shared state, and no user control. I'd like to propose a smaller design that answers both, and I'm happy to implement it if you approve the direction.

1. Ephemeral state.

• The server reads the SDK's prompt_suggestion message. It is sent after result, so the adapter must keep reading the stream after the turn ends.
• The server forwards it as a transient event to connected web and desktop clients only. No persisted activity, no shared activity contract change, no sync to other clients.
• The client keeps one suggestion per thread in memory. It clears the suggestion when the user types, sends a message, switches thread, or dismisses it.

2. Explicit control.

• A Claude provider setting, "Prompt suggestions", turns promptSuggestions on or off. It is off by default.
• When it is off, the adapter never sets the SDK option.

3. Scope.

• The first PR covers web and desktop only. Tab accepts the suggestion and Esc dismisses it. Mobile is left for later.
• Codex follow-ups are not touched.

Questions

• Is off by default the right choice, or should it be on?
• Should a transient event type be added to the existing provider event stream, or is there a better channel for session-only data?
• Is web and desktop only acceptable for a first PR?

I'd follow the one-problem rule and send the PR only after a maintainer approves the direction.

[tobymarks]

+1 from a daily T3 user (macOS desktop, Claude provider). This is the Claude Code feature I miss most since switching.

On @thedrowsywinger's questions, from a user's point of view:

• Default: Off is fine. A "Prompt suggestions" toggle under the Claude provider settings is where I'd look for it first.
• Accepting: Tab to accept and Esc to dismiss, like in the Claude Code CLI. Accepting should only fill the composer, never send.
• Scope: Web and desktop first works for me, since that's where I use it.

The ephemeral design also matches how I'd use it. The suggestion only matters right after a turn finishes, so I wouldn't expect it to survive a restart or show up on another device.

@thedrowsywinger if the direction gets approved, I'm happy to help test on macOS or take a part of the implementation.

[tobymarks]

I built the smaller design from @thedrowsywinger's comment on a fork to check that it holds up: tobymarks/t3code@feat/claude-prompt-suggestions

• Ephemeral: The latest suggestion per thread lives in an in-memory store on the server. It is cleared when the next turn starts or the session closes, and clients read it through a stream that only lives in memory. It is not persisted, not added to thread activities, and no activity contracts change.
• Opt-in: There is a "Prompt suggestions" switch in the Claude provider settings, off by default. When it is off, promptSuggestions is never passed to the SDK.
• Web/desktop only: The suggestion is the empty composer's placeholder. Tab fills the draft and never sends. Esc hides it. Mobile is untouched.

I tested it in a dev build with Claude Sonnet 5.5 and added focused tests for the adapter and the store. One finding: the CLI did emit a suggestion after the first turn, even though the SDK typings say it is suppressed there.

Setting (off by default)	Suggestion in the empty composer	After Tab

@thedrowsywinger this isn't meant to take over your proposal. If the direction is approved, feel free to use any of it, or I can open the PR, whichever you and the maintainers prefer.

[danielyc]

I opened a PR for this: #17618.

It builds on @tobymarks' fork. Suggestions appear as placeholder ghost text: Tab fills the draft and Esc hides it. The toggle lives under Settings → Providers → Claude and is off by default. It also follows the close note on #8524:

• The suggestion lives only in server memory and has its own subscription instead of going through the activity contract.
• Mobile is unchanged.
• The suggestion is cleared when the next turn starts, after a background wake, after a rollback and when the session closes. The client only shows it while the run it follows is still the latest.

Feedback on the product behavior is very welcome. I'm happy to adjust it.