feat(workspace): add localStorage helper for split-view layout state

client/src/lib/splitViewStorage.ts

@@ -0,0 +1,54 @@
+/**
+ * @file splitViewStorage.ts
+ * @description Persists the Workspace page's split-terminal layout (1/2/4
+ * panes) and each pane's chosen lane id to localStorage, so the layout
+ * survives a page reload. Follows the same read/write-with-fallback
+ * convention as useTheme.ts.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+export type SplitLayout = 1 | 2 | 4;
+
+export interface SplitViewState {
+  layout: SplitLayout;
+  paneLaneIds: (number | null)[];
+}
+
+const STORAGE_KEY = "ccam.workspace.splitView";
+
+export function defaultSplitViewState(): SplitViewState {
+  return { layout: 1, paneLaneIds: [null] };
+}
+
+function isValidLayout(value: unknown): value is SplitLayout {
+  return value === 1 || value === 2 || value === 4;
+}
+
+function isValidState(value: unknown): value is SplitViewState {
+  if (!value || typeof value !== "object") return false;
+  const v = value as Record<string, unknown>;
+  return (
+    isValidLayout(v.layout) &&
+    Array.isArray(v.paneLaneIds) &&
+    v.paneLaneIds.every((id) => id === null || typeof id === "number")
+  );
+}
+
+export function readSplitViewState(): SplitViewState {
+  try {
+    const raw = localStorage.getItem(STORAGE_KEY);
+    if (!raw) return defaultSplitViewState();
+    const parsed: unknown = JSON.parse(raw);
+    return isValidState(parsed) ? parsed : defaultSplitViewState();
+  } catch {
+    return defaultSplitViewState();
+  }
+}
+
+export function writeSplitViewState(state: SplitViewState): void {
+  try {
+    localStorage.setItem(STORAGE_KEY, JSON.stringify(state));
+  } catch {
+    /* ignore quota / disabled storage */
+  }
+}