fix(app): working scrollback search + stop prompt duplication on focus

Search fixes:
- TerminalView sets allowProposedApi (the search addon's match decorations
  use registerMarker/registerDecoration); without it findNext threw before
  firing results, so the counter was stuck at 0/0.
- The search bar now renders inside the panel it targets (in the header)
  instead of a global top-right overlay, so it's obvious which panel is
  searched.
- Search is anchored to the panel it was opened on (searchSurfaceId) and no
  longer follows focus — opening it in one panel and switching away no longer
  shows it open elsewhere.

Prompt duplication:
- The focus border was 1px when unfocused, 2px when focused; with border-box
  that resized the content on every focus switch, firing ResizeObserver -> fit
  -> PTY SIGWINCH and making zsh/powerlevel10k reprint its prompt. The border
  is now a constant 2px, color-only on focus.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/LayoutEngine.tsx

@@ -1,6 +1,7 @@
 import { useEffect, useRef, useState } from "react";
 import { Maximize2, Minimize2, RotateCw, GripVertical } from "lucide-react";
 import { TerminalView } from "./TerminalView";
+import { SearchBar } from "./SearchBar";
 import { StatusRing } from "./StatusRing";
 import { COLORS, FONT, STATE_COLOR } from "./theme";
 import type { LayoutNode, SurfaceState, SurfaceView } from "./layoutTypes";
@@ -16,6 +17,11 @@ interface Props {
   focusedId: string | null;
   onFocus: (id: string) => void;
   zoomed: string | null;
+  /** The surface whose scrollback search bar is open, or null. Anchored to the
+   * panel it was opened on — it does NOT follow focus. */
+  searchSurfaceId: string | null;
+  searchNonce: number;
+  onCloseSearch: () => void;
 }
 
 type Edge = "left" | "right" | "top" | "bottom";
@@ -34,7 +40,7 @@ function shortPath(cwd: string): string {
   return leaf ? `~/${leaf}` : cwd;
 }
 
-export function LayoutEngine({ workspaceId, layout, running, states, surfaces, focusedId, onFocus, zoomed }: Props) {
+export function LayoutEngine({ workspaceId, layout, running, states, surfaces, focusedId, onFocus, zoomed, searchSurfaceId, searchNonce, onCloseSearch }: Props) {
   // Panel drag-to-reorder. Implemented with raw pointer events rather than the
   // HTML5 drag API, which is unreliable in the macOS WKWebView Tauri uses.
   const [drop, setDrop] = useState<DropTarget | null>(null);
@@ -72,7 +78,7 @@ export function LayoutEngine({ workspaceId, layout, running, states, surfaces, f
   if (!layout) {
     return <div style={{ color: COLORS.textMuted, padding: 24 }}>Empty workspace — apply a preset to add panels.</div>;
   }
-  const shared = { workspaceId, running, states, surfaces, focusedId, onFocus, zoomed, drop, onStartPanelDrag: startPanelDrag };
+  const shared = { workspaceId, running, states, surfaces, focusedId, onFocus, zoomed, drop, onStartPanelDrag: startPanelDrag, searchSurfaceId, searchNonce, onCloseSearch };
   if (zoomed) {
     return (
       <div style={{ width: "100%", height: "100%", padding: 12, boxSizing: "border-box" }}>
@@ -94,6 +100,9 @@ interface NodeProps {
   zoomed: string | null;
   drop: DropTarget | null;
   onStartPanelDrag: (srcId: string, e: React.MouseEvent) => void;
+  searchSurfaceId: string | null;
+  searchNonce: number;
+  onCloseSearch: () => void;
 }
 
 function Node({ node, path, ...rest }: NodeProps) {
@@ -103,7 +112,7 @@ function Node({ node, path, ...rest }: NodeProps) {
   return <SplitView split={node.split} path={path} {...rest} />;
 }
 
-function Leaf({ id, workspaceId, running, states, surfaces, focusedId, onFocus, zoomed, drop, onStartPanelDrag }: Omit<NodeProps, "node" | "path"> & { id: string }) {
+function Leaf({ id, workspaceId, running, states, surfaces, focusedId, onFocus, zoomed, drop, onStartPanelDrag, searchSurfaceId, searchNonce, onCloseSearch }: Omit<NodeProps, "node" | "path"> & { id: string }) {
   const focused = focusedId === id;
   const dropEdge = drop && drop.id === id ? drop.edge : null;
 
@@ -114,7 +123,11 @@ function Leaf({ id, workspaceId, running, states, surfaces, focusedId, onFocus,
       style={{
         position: "relative", display: "flex", flexDirection: "column", width: "100%", height: "100%",
         background: COLORS.bgPanel, borderRadius: 8, overflow: "hidden",
-        border: focused ? `2px solid ${COLORS.accent}` : `1px solid ${COLORS.borderSubtle}`,
+        // Constant 2px border, color-only on focus. A width change (1px<->2px)
+        // would resize the inner content box, fire ResizeObserver -> fit -> PTY
+        // SIGWINCH, making zsh/powerlevel10k reprint its prompt on every focus
+        // switch (the "stacked prompts" bug).
+        border: `2px solid ${focused ? COLORS.accent : COLORS.borderSubtle}`,
         boxSizing: "border-box",
       }}
     >
@@ -170,6 +183,9 @@ function Leaf({ id, workspaceId, running, states, surfaces, focusedId, onFocus,
       <div style={{ flex: 1, minHeight: 0 }}>
         <TerminalView key={id} surfaceId={id} />
       </div>
+      {searchSurfaceId === id && (
+        <SearchBar surfaceId={id} reopenNonce={searchNonce} onClose={onCloseSearch} />
+      )}
     </>
   );
 }