feat(unsaved-changes): implement utility for detecting and handling unsaved changes

src/lib/client/ui/modal/UnsavedChangesModal.svelte

@@ -0,0 +1,31 @@
+<script lang="ts">
+	import { beforeNavigate, goto } from '$app/navigation';
+	import Modal from './Modal.svelte';
+	import { useUnsavedChanges } from '$lib/client/utils/unsavedChanges.svelte';
+
+	const unsavedChanges = useUnsavedChanges();
+	let pendingNavigationUrl: string | null = null;
+
+	beforeNavigate(async (navigation) => {
+		if (unsavedChanges.isDirty) {
+			navigation.cancel();
+			pendingNavigationUrl = navigation.to?.url.pathname || null;
+			const shouldNavigate = await unsavedChanges.confirmNavigation();
+			if (shouldNavigate && pendingNavigationUrl) {
+				goto(pendingNavigationUrl);
+			}
+			pendingNavigationUrl = null;
+		}
+	});
+</script>
+
+<Modal
+	open={unsavedChanges.showModal}
+	header="Unsaved Changes"
+	bodyMessage="You have unsaved changes. Are you sure you want to leave this page? Your changes will be lost."
+	confirmText="Discard Changes"
+	cancelText="Stay on Page"
+	confirmDanger={true}
+	on:confirm={() => unsavedChanges.confirmDiscard()}
+	on:cancel={() => unsavedChanges.cancelDiscard()}
+/>

src/lib/client/utils/unsavedChanges.svelte.ts

@@ -0,0 +1,78 @@
+/**
+ * Utility for detecting and handling unsaved changes
+ */
+
+let hasUnsavedChanges = $state(false);
+let showWarningModal = $state(false);
+let resolveNavigation: ((value: boolean) => void) | null = null;
+
+export function useUnsavedChanges() {
+	return {
+		/**
+		 * Mark the page as having unsaved changes
+		 */
+		markDirty() {
+			hasUnsavedChanges = true;
+		},
+
+		/**
+		 * Mark the page as clean (changes saved)
+		 */
+		markClean() {
+			hasUnsavedChanges = false;
+		},
+
+		/**
+		 * Check if there are unsaved changes
+		 */
+		get isDirty() {
+			return hasUnsavedChanges;
+		},
+
+		/**
+		 * Get modal state
+		 */
+		get showModal() {
+			return showWarningModal;
+		},
+
+		/**
+		 * Request navigation confirmation
+		 * Returns a promise that resolves to true if navigation should proceed
+		 */
+		confirmNavigation(): Promise<boolean> {
+			if (!hasUnsavedChanges) {
+				return Promise.resolve(true);
+			}
+
+			showWarningModal = true;
+
+			return new Promise((resolve) => {
+				resolveNavigation = resolve;
+			});
+		},
+
+		/**
+		 * User confirmed navigation (discard changes)
+		 */
+		confirmDiscard() {
+			showWarningModal = false;
+			hasUnsavedChanges = false;
+			if (resolveNavigation) {
+				resolveNavigation(true);
+				resolveNavigation = null;
+			}
+		},
+
+		/**
+		 * User cancelled navigation (stay on page)
+		 */
+		cancelDiscard() {
+			showWarningModal = false;
+			if (resolveNavigation) {
+				resolveNavigation(false);
+				resolveNavigation = null;
+			}
+		}
+	};
+}