feat: add persistent dynamic panels

docs/TESTING.md

@@ -124,9 +124,12 @@ who already have the final cargo-watch release installed.
 - The GPUI slice tests its key-event adapter, responsive one/three/five-panel
   geometry, selected-panel windowing, per-panel 20/60/20 PTY sizing, xterm
   256-color conversion, styled-run coalescing, cursor-run boundaries, and
-  scrollback shortcut routing. It renders three independently actor-owned VT
-  sessions while three non-terminal surfaces continue their deterministic
-  background workload.
+  scrollback shortcut routing. Its panel registry tests monotonic identity,
+  insert-beside-selection, detach/reattach identity preservation, snapshot
+  validation, SQLite round-trip, and refusal to reuse a restored ID. It renders
+  an independent actor-owned VT session for every Terminal panel while the
+  original three non-terminal surfaces continue their deterministic background
+  workload.
 - `lumbridge-terminal` retains 10,000 history lines by default and tests
   framework-neutral page/top/bottom viewport movement, revision changes, and
   live-bottom no-ops without sending history-navigation bytes to the child PTY.