feat(app): keep workspace tabs alive in panes

packages/app/src/screens/workspace/use-mounted-tab-set.ts

@@ -0,0 +1,64 @@
+import { useLayoutEffect, useMemo, useRef, useState } from "react";
+
+interface UseMountedTabSetInput {
+  activeTabId: string | null;
+  allTabIds: string[];
+  cap: number;
+}
+
+interface UseMountedTabSetResult {
+  mountedTabIds: Set<string>;
+}
+
+function createInitialMountedTabIds(input: UseMountedTabSetInput): Set<string> {
+  if (!input.activeTabId || !input.allTabIds.includes(input.activeTabId)) {
+    return new Set<string>();
+  }
+  return new Set<string>([input.activeTabId]);
+}
+
+function setsEqual(left: Set<string>, right: Set<string>): boolean {
+  if (left.size !== right.size) {
+    return false;
+  }
+  for (const value of left) {
+    if (!right.has(value)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+export function useMountedTabSet(input: UseMountedTabSetInput): UseMountedTabSetResult {
+  const { activeTabId, allTabIds, cap } = input;
+  const allTabIdsKey = allTabIds.join("\u0000");
+  const availableTabIds = useMemo(() => new Set(allTabIds), [allTabIdsKey]);
+  const [mountedTabIds, setMountedTabIds] = useState(() => createInitialMountedTabIds(input));
+  const lruRef = useRef(
+    activeTabId && allTabIds.includes(activeTabId) ? [activeTabId] : [],
+  );
+
+  useLayoutEffect(() => {
+    const nextLru = lruRef.current.filter((tabId) => availableTabIds.has(tabId));
+    if (activeTabId && availableTabIds.has(activeTabId)) {
+      const existingIndex = nextLru.indexOf(activeTabId);
+      if (existingIndex >= 0) {
+        nextLru.splice(existingIndex, 1);
+      }
+      nextLru.unshift(activeTabId);
+    }
+    if (nextLru.length > cap) {
+      nextLru.length = cap;
+    }
+
+    lruRef.current = nextLru;
+    setMountedTabIds((previousMountedTabIds) => {
+      const nextMountedTabIds = new Set(nextLru);
+      return setsEqual(previousMountedTabIds, nextMountedTabIds)
+        ? previousMountedTabIds
+        : nextMountedTabIds;
+    });
+  }, [activeTabId, availableTabIds, cap]);
+
+  return { mountedTabIds };
+}