fix(maestro): keep the keyboard in the list while previewing

Two mounts were taking focus out of the sidebar mid-walk: the render that
put the multi-view on screen before the preview applied, and the render
that restores the previous pane when a preview ends. Both now mount
without focusing, so j/k keeps walking. Also marks the preview with a
badge on the canvas and drops the close button from its tab.

web/src/multiview.ts

@@ -110,6 +110,20 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     tempTabId: string | null;
   }
   let preview: Preview | null = null;
+  /// Set while a preview-driven render runs: ending a preview re-mounts the
+  /// pane that was there, and that mount must not pull the keyboard out of the
+  /// sidebar the operator is still walking.
+  let quietRender = false;
+
+  /** Render without any mount taking the keyboard. */
+  function renderQuietly(): void {
+    quietRender = true;
+    try {
+      render();
+    } finally {
+      quietRender = false;
+    }
+  }
 
   const isTempTab = (tabId: string) => preview?.tempTabId === tabId;
 
@@ -152,7 +166,7 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
   function previewSession(sessionId: string | null): void {
     if (preview?.sessionId === sessionId) return;
     if (sessionId === null) {
-      if (restorePreview()) render();
+      if (restorePreview()) renderQuietly();
       return;
     }
     restorePreview();
@@ -176,7 +190,7 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
       layout.activeTabId = tab.id;
       preview = { sessionId, prevActiveTabId, prevFocus: null, tempTabId: tab.id };
     }
-    render();
+    renderQuietly();
   }
 
   /** Any user action that changes the layout for real ends the preview first,
@@ -385,7 +399,8 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
         }
         render();
       });
-      if (layout.tabs.length > 1) {
+      // A preview tab is not the operator's to close: it goes on its own.
+      if (layout.tabs.length > 1 && !isTempTab(t.id)) {
         const close = document.createElement("span");
         close.className = "mv-tab-close";
         close.textContent = "✕";
@@ -555,7 +570,7 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     // terminal, or j/k would stop walking the list after the first step.
     pool.setVisible(
       hosts.map((h) => ({ id: h.id, pane: h.host, info: h.info })),
-      { focus: !preview },
+      { focus: !preview && !quietRender },
     );
     syncFocus();
     persist();
@@ -579,7 +594,7 @@ export function createMultiView(opts: MultiViewOptions): MultiView {
     // Only the focused leaf's session is live on mobile; the rest park.
     pool.setVisible(
       focused.sessionId ? [{ id: focused.sessionId, pane: pane.host, info: infoFor(focused.sessionId) }] : [],
-      { focus: !preview },
+      { focus: !preview && !quietRender },
     );
     if (!preview) pool.setFocus(focused.sessionId ?? null);
     sidebar.setHighlights({ open: realOpenSessions(), focused: focused.sessionId ?? null });