[eric] browser: keep recent browsers alive across dashboard switches so sessions survive

frontend/src/shared/browserFocus.ts

@@ -1,11 +1,13 @@
-// Tracks which browser card the user last interacted with (clicked into its page or its chrome),
-// so global shortcuts (Ctrl+R reload, Ctrl +/- zoom, Ctrl+Tab) target THAT browser instead of a
-// guess. Module-level and imperative on purpose: shortcut handlers read it on keydown, so no React
-// re-render is needed. Cleared the moment the user clicks anything that isn't a browser card.
+// The browser card you last clicked into, so global shortcuts (Ctrl+R, zoom, Ctrl+Tab) target it; imperative + read on keydown so no re-render, and cleared the moment you click off any browser card.
 let lastInteractedBrowserId: string | null = null;
 
+// Recently-used browser ids, newest first; the top KEEP_ALIVE_CAP stay mounted across dashboard switches + off-screen so their sessionStorage (logins like Discord) survives, the rest get reclaimed by the normal suspend (LRU).
+const KEEP_ALIVE_CAP = 4;
+let recentBrowserIds: string[] = [];
+
 export function setLastInteractedBrowser(browserId: string): void {
   lastInteractedBrowserId = browserId;
+  recentBrowserIds = [browserId, ...recentBrowserIds.filter((id) => id !== browserId)].slice(0, 32);
 }
 
 export function clearLastInteractedBrowser(): void {
@@ -15,3 +17,17 @@ export function clearLastInteractedBrowser(): void {
 export function getLastInteractedBrowser(): string | null {
   return lastInteractedBrowserId;
 }
+
+export function getKeepAliveBrowserIds(): string[] {
+  return recentBrowserIds.slice(0, KEEP_ALIVE_CAP);
+}
+
+export function isKeepAliveBrowser(browserId: string): boolean {
+  return getKeepAliveBrowserIds().includes(browserId);
+}
+
+// Drop a closed browser from focus + keep-alive tracking so a dead id can't hog a slot.
+export function forgetBrowser(browserId: string): void {
+  recentBrowserIds = recentBrowserIds.filter((id) => id !== browserId);
+  if (lastInteractedBrowserId === browserId) lastInteractedBrowserId = null;
+}