Bindable line-by-line timeline scrolling from the composer (e.g. Shift+↑/↓), plus focus commands

[rsaulo]

Problem

From the composer, the only keyboard way to move the thread is PageUp/PageDown. The composer forwards those two keys to the timeline, but each press moves a whole screen. There is no way to nudge the thread by a line or a few lines while you keep typing. That is what you want when re-reading the end of a long reply, or checking a code block just above the fold before answering.

The timeline does handle ↑/↓ (plus Home/End and PageUp/PageDown), but only when focus is outside the composer. The document-level handler bails out on any modifier, and the composer keeps arrow keys for caret movement. So line scrolling means:

1. leaving the composer, which needs a mouse click because there is no focus command,
2. pressing ↑/↓,
3. clicking back into the composer.

None of the three steps can be done from the keyboard, and none can be remapped. KeybindingCommand has no scroll or focus commands, so keybindings.json can't fill the gap either.

Proposal

Add bindable timeline-scroll commands that work while the composer has focus, using the same path that already forwards PageUp/PageDown:

Command	Action
thread.scrollLineUp / thread.scrollLineDown	Scroll the timeline by one line step, about the browser's arrow-key distance
(optional) thread.scrollHalfPageUp / thread.scrollHalfPageDown	Half a screen, for finer control than PageUp/PageDown

I'd bind shift+arrowup / shift+arrowdown with when: "!terminalFocus". That is the shortcut I actually want. It does conflict with extending a text selection in the composer, so it probably shouldn't ship as a default. Following the precedent of #16657 (thread.previousTurn / thread.nextTurn), the commands could ship unbound and let users pick. Two other options:

• apply them only when the composer has no selection, or
• apply them only when the caret is on the first or last line of the draft.

Holding the key should repeat smoothly, as holding PageUp/PageDown already does.

Related, smaller: focus commands

Keyboard-heavy use also needs a way to move focus between the composer and the timeline:

• composer.focus: this was implemented in feat(web): add configurable composer focus shortcut #10910, unbound by default and reviewed favourably, then closed only because it conflicted with the orchestrator V2 rewrite (feat(orchestrator): introduce new orchestrator #2829), not on merit. It is also item 5 in [Feature]: Expose more actions as bindable keybinding commands #6817.
• thread.focusTimeline: move focus to the timeline so ↑/↓/Home/End work there, then use composer.focus to come back.

With the scroll commands, most people wouldn't need to leave the composer at all. The focus commands cover the rest.

Environment

T3 Code 0.0.46-nightly.20261007.2774 (desktop), macOS 27.0.1.

Related

• feat(web): add bindable commands to jump between turns #16657 adds bindable turn-jump commands, the same pattern at a coarser step
• feat(web): add configurable composer focus shortcut #10910 added composer.focus and was closed in the V2 transition
• [Feature]: Expose more actions as bindable keybinding commands #6817 tracks exposing more actions as bindable commands