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.