feat(web): add workspace panes and transitions - #28845

…d it

…case

Checks visible timeline lists a second after a turn ends, the fold
collapses, the thread is shown or the row count changes, confirms the gap
a few seconds later, keeps the last 20 reports in localStorage and shows
one toast per thread with a copy action. Exposes window.t3dev.gapReports,
copyGapReports and checkGapsNow. Remove once the gap's cause is fixed.

A pull request open as a tab beside a chat answered only the copy-number shortcut, so Cmd+Shift+C did nothing there. The pull request detail now answers copy link while its pane is focused, through the same copy target and confirmation as the thread and the Pull requests page.

… them up with rows

Each tab's header rendered its own tab strip, so switching tabs swapped
the strip out from under anything drawn in it. The strip is now one node
per pane that the shown header holds; each header portals its tabs into
its own layer, which stays mounted while the header is hidden and moves
into the strip when it shows. The strip carries the joined tab's shape,
placed under the active tab once per tab change and hidden until the
connected pane tabs draw it. Looks unchanged.

From md up, a pane's top is a bar in the chrome's color. The focused
pane's active tab is a piece of the pane rising into it, joined by
concave ears, with one lit rim from its top round the ears and 36px out
along the pane's edge, where it fades. An unfocused pane's active tab is
a soft pill. Switching tabs slides the shape to the new tab over the
panel animation duration with ease-out, transform only, and the labels
fade between tiers on the same clock; focus moving between panes
cross-fades the shape and the pill. Reduced motion and a duration of 0
turn both off.

Light, black chrome keeps today's notch: its paint is scoped to
.black-chrome and the modal pane, so it can be deleted on its own.

On the connected bar the joined tab names its kind (Diff, Files) and its
breadcrumb and scope controls follow it on the bar as plain controls, so
a wide breadcrumb no longer stretches the joined tab out of the strip.
The breadcrumb gives way before the tabs when the pane is narrow. Black
chrome and phones keep it inside the tab.

…when it lands

The shape waited for the switch's commit and the incoming chat's layout,
about 120 ms, while the labels changed at once. It now starts sliding on
the press, measured from the tabs as they are, on its own compositor
layers, so it keeps moving while the switch renders; a press that does not
end in that tab showing brings it back. Labels read as active only under
the landed shape. Every title gets the active one's room, so activating a
tab moves no other tab. Where tabs are scrolled out, the strip fades at
that edge as scroll areas do.

… half-width pane

On the bar the breadcrumb shares the row with the pane's tabs, so the diff
treats it as crowded: the head ref folds away below 36rem and the view
controls fold into their menu, leaving the scope and the base in full.

The text field mic becomes the composer's bars and x where it sits, the
live transcript streams into the field itself, and errors take the same
slot, so no row is added and the buttons beside it stay put.

…emselves on hover

Main's details-panel test drops the timeline registrar the canvas context no longer carries.

… redesign's default

The suggestion and the composer placeholder now share the editor's text box,
line height and wrapping, so Tab no longer nudges the words or resizes the
composer. The Tab hint can't add a line and hides when it doesn't fit. The
sidebar rename field keeps the title's line height.

… button and the timeline steady

The sidebar slide moved the whole pane as one block from its final layout,
so everything anchored to the right edge or centered took a detour: the
details card swung 248px, the details button was clipped out of view while
opening, and the timeline and composer jumped 213px before sliding back.
Elements marked data-sidebar-slide-track now go straight from where they
were to where they land, the slide waits for the chat lanes' resize
observers before measuring, and while opening the pane clips by its shape
so what stays at its right edge stays visible.

…imer

A new worktree's checkout and setup script now show as ordinary work rows under
"Working for", which counts from send through setup into the agent's work. When
setup ends the stages fold into one "Set up worktree" row that opens on click.
A failed or cancelled setup keeps its stage rows above the run's own outcome.
Runs that prepared a worktree carry that fact on their summary, so the final
"Worked for" counts from send too.

…otion

Moves the track edge, the wait for resize observers and the clip lifting
out of sidebar.tsx into motion/slideTrack.ts, unchanged.

Opening the diff, files or terminal panel, splitting or closing a pane,
and toggling the sidebar beside split panes now move every pane edge,
the details button, the tab bar's end corner, the timeline and the
composer straight from where they were to where they land, together.

Before, the pane making room resized on the first frame (timeline and
details button jumped up to 532px) while the new pane slid into an empty
gap for 326ms on a spring; beside split panes the sidebar slide moved the
edge between them 136px the wrong way and back.

Pane motion now uses the sidebar slide's ease-out for the Panel
animations duration, snapshots tracked elements before React commits a
new layout, and slides them from there once the chat lanes re-measure,
keeping lanes on their pane's steady side. A sidebar toggle hands split
panes to pane motion with a snapshot taken before its own commit.