feat(schema-diff): support selecting tables to compare

apps/desktop/src/lib/diff/tableMultiSelect.ts

@@ -0,0 +1,43 @@
+/**
+ * Pure selection/filtering helpers for the shared TableMultiSelect UI.
+ *
+ * These are framework-agnostic (no Vue state) so the behavior of the shared
+ * multi-table selector can be unit-tested independently of any component
+ * mount infrastructure, and so the same logic backs both Data Compare and
+ * Schema Diff table selection.
+ */
+
+/** Case-insensitive substring filter over table names. An empty/whitespace query returns all tables. */
+export function filterTableNames(tables: string[], query: string): string[] {
+  const trimmed = query.trim().toLowerCase();
+  if (!trimmed) return tables;
+  return tables.filter((table) => table.toLowerCase().includes(trimmed));
+}
+
+/** Toggle a single table name within a selection list (preserves order, no duplicates). */
+export function toggleTableName(selected: string[], table: string): string[] {
+  if (selected.includes(table)) {
+    return selected.filter((name) => name !== table);
+  }
+  return [...selected, table];
+}
+
+/** True when every entry of `filtered` is already present in `selected`. */
+export function isEveryFilteredSelected(selected: string[], filtered: string[]): boolean {
+  return filtered.length > 0 && filtered.every((table) => selected.includes(table));
+}
+
+/**
+ * Select every table in `filtered` if not all are selected; otherwise deselect them all.
+ * Only tables within `filtered` are touched — the rest of `selected` is preserved, so
+ * selecting-all after a search only affects the current filtered subset.
+ */
+export function toggleSelectFiltered(selected: string[], filtered: string[]): string[] {
+  const next = new Set(selected);
+  if (isEveryFilteredSelected(selected, filtered)) {
+    filtered.forEach((table) => next.delete(table));
+  } else {
+    filtered.forEach((table) => next.add(table));
+  }
+  return [...next];
+}