feat: make terminal the primary workspace surface

docs/UX_VERTICAL_SLICE.md

@@ -9,15 +9,13 @@ framework decision gate, not a decorative dashboard.
 
 ## Current-run audit
 
-The 2026-08-31 GPUI baseline succeeds at calm density: the six surfaces are easy
-to scan, typography is consistent, and local/remote targets remain visible. It
-fails the task flow in four important ways:
-
-1. all panes have equal visual priority, so `NEEDS INPUT` is too easy to miss;
-2. no pane exposes visible keyboard focus or selection;
-3. the command palette affordance has no interaction behind it;
-4. status and usage text in the footer is too quiet to explain provenance or
-   confidence at a glance.
+The first 2026-08-31 GPUI baseline proved six-surface density but gave every
+pane equal visual priority. The current slice replaces that dashboard with a
+3×1 default: 20% context and pane selection, 60% active work surface, and 20%
+decision shelf. Keyboard focus, command-palette input, live PTY input, styled VT
+cells, cursor shapes, and geometry-driven resize are wired. Remaining visible
+gaps are terminal selection/scrollback, real decision-shelf actions, usage-detail
+provenance, and end-to-end platform accessibility/IME.
 
 Screenshots for the audit are stored outside Git under
 `~/shots/2026-08/lumbridge-ui-audit/`. Accessibility and IME correctness cannot
@@ -60,11 +58,12 @@ surface rather than a hosted Lumbridge control plane.
    palette shortcut.
 2. The sidebar starts with a compact `ATTENTION` group, followed by workspaces
    and remote hosts. It does not become a notification feed.
-3. The active pane receives a two-pixel accent edge plus a quiet tinted header.
-4. A waiting pane uses an amber semantic label and remains visible when another
-   pane is selected. The label always includes words such as `NEEDS INPUT`.
-5. Pane headers expose title, execution target, harness state, and unread count
-   in a stable order.
+3. A compact top 20% context band keeps all pane identities and states visible;
+   the selected pane receives the accent treatment.
+4. A waiting pane uses an amber semantic label in both the context band and
+   attention sidebar. The label always includes words such as `NEEDS INPUT`.
+5. The middle 60% gives the selected terminal or work surface uninterrupted
+   reading space and retains target, harness state, dimensions, and surface tabs.
 6. The footer groups connection state, selected-harness identity, usage-window
    provenance, and burn forecast into readable regions.
 7. The selected pane has a quiet surface strip for Terminal, Browser, Tools,
@@ -75,7 +74,7 @@ surface rather than a hosted Lumbridge control plane.
 
 ## Keyboard task flow
 
-- `Alt+Arrow` or `Alt+h/j/k/l`: move focus through the 2×3 pane grid while
+- `Alt+Arrow` or `Alt+h/j/k/l`: move selection through the pane topology while
   leaving ordinary terminal arrows and text available to the PTY.
 - `Alt+1` through `Alt+6`: focus a pane directly while leaving terminal digits
   available to the PTY.
@@ -93,8 +92,8 @@ receive the same state transitions and tests.
 
 - In the first actor integration, one terminal pane consumes ordered output from
   a real local PTY while each deterministic tick updates the other five
-  surfaces. The all-deterministic constructor remains available for framework
-  comparison and replay tests.
+  surfaces offscreen. The all-deterministic constructor remains available for
+  framework comparison and replay tests.
 - One pane enters and leaves `needs input` through a deterministic event.
 - Markdown, browser-boundary, and review panes update counters without using a
   web application shell.
@@ -103,7 +102,8 @@ receive the same state transitions and tests.
   element-build timing is never presented as display-present timing.
 - The PTY actor replaces exactly one synthetic stream without changing focus or
   layout contracts. Synthetic streams stay available for repeatable performance
-  tests. Raw lines do not claim terminal-emulation fidelity.
+  tests. Live bytes are parsed into VT state and coalesced native paint runs;
+  deterministic fixture text makes no terminal-emulation claim.
 
 ## Hard gates