Add bounded runtime actor and live PTY pane

docs/UX_VERTICAL_SLICE.md

@@ -84,16 +84,19 @@ receive the same state transitions and tests.
 
 ## Decisive workload
 
-- One deterministic tick invalidates all six surfaces and appends bounded output
-  to the three terminal panes. Framework adapters consume the same event trace.
+- 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.
 - 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.
 - The model records actions, revisions, six-surface updates, and bounded terminal
   line counts. Framework adapters label each measured timing stage explicitly;
   element-build timing is never presented as display-present timing.
-- A later PTY adapter replaces one synthetic stream without changing the UI
-  contract. Synthetic streams stay available for repeatable performance tests.
+- 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.
 
 ## Hard gates