[Feature]: Keep the active agent in view in the Agents panel during long sessions

[directfilm]

Problem

In long-lived threads that spawn a lot of subagents, the Agents panel keeps agents in first-seen order and never moves. After a few dozen agents the running one is well below the fold, so checking on live work means scrolling to the bottom of the panel every single time.

Why this is a new thread

#7324 raised this exact pain ("the newest and usually most relevant agent can land below the visible area") and proposed newest-first ordering. It was closed on 2026-09-04 by the automated cleanup pass, which said:

This closure does not mean the proposed ordering was implemented. Please use Ideas for that choice.

So this is that Ideas thread — but with a different solution, because I think the ordering approach was the weaker one.

Proposal

Keep first-seen order. Auto-scroll the panel to the newest agent when one is spawned.

#7324 was careful to preserve stable rows during progress updates, but newest-first has a cost it can't avoid: every new spawn pushes every existing row down, so the list shifts under you exactly when a burst of agents starts. Auto-scroll gets the same visibility without changing the order, and without the list reordering itself while you read it.

Standard stick-to-bottom semantics, the same rule the chat transcript already uses:

• Follow the newest agent while the panel is scrolled to the bottom.
• The moment the user scrolls up, stop following — never yank the viewport away from something being read.
• When scrolled away with new activity below, show a small "jump to active" affordance to get back.

Relationship to #6925

#6925 asks to clear settled and idle agents from the panel. That is the complementary half and I am not restating it here — together they mean the panel shows what is actually live rather than a session-long archive. Either is useful alone; both together fix the problem properly.

Environment

T3 Code Nightly 0.0.39-nightly.20260904.1274, macOS 26.6.2.