fix: Address critical issues in admin form refactor

Phase 1: Critical Type Fixes
- Fix useDraftRecovery type signature to accept () => string | null
  (was incorrectly typed as string | null)
- Add TResponse generic parameter to AutoSaveStore interface
- Update all call sites to use function for draftKey reactivity

Phase 2: Robustness Improvements
- Remove non-null assertions in useFormGuards
- Capture autoSave in closures to prevent potential null access
- Make useFormGuards generic to accept any AutoSaveStore types

Documentation & Code Quality
- Document AlbumForm autosave initialization order
- Add comments explaining void operator usage for reactivity
- Fix eslint error: prefix unused _TResponse with underscore

These fixes address the critical issues found in PR review:
1. Type mismatch causing TypeScript errors
2. Non-null assertions that could cause crashes
3. Missing documentation for complex initialization patterns

src/lib/admin/autoSave.svelte.ts

@@ -8,7 +8,7 @@ export interface AutoSaveStoreOptions<TPayload, TResponse = unknown> {
   onSaved?: (res: TResponse, ctx: { prime: (payload: TPayload) => void }) => void
 }
 
-export interface AutoSaveStore<TPayload> {
+export interface AutoSaveStore<TPayload, _TResponse = unknown> {
   readonly status: AutoSaveStatus
   readonly lastError: string | null
   schedule: () => void
@@ -36,7 +36,7 @@ export interface AutoSaveStore<TPayload> {
  */
 export function createAutoSaveStore<TPayload, TResponse = unknown>(
   opts: AutoSaveStoreOptions<TPayload, TResponse>
-): AutoSaveStore<TPayload> {
+): AutoSaveStore<TPayload, unknown> {
   const debounceMs = opts.debounceMs ?? 2000
   const idleResetMs = opts.idleResetMs ?? 2000
   let timer: ReturnType<typeof setTimeout> | null = null

src/lib/admin/useDraftRecovery.svelte.ts

@@ -1,7 +1,7 @@
 import { loadDraft, clearDraft, timeAgo } from '$lib/admin/draftStore'
 
 export function useDraftRecovery<TPayload>(options: {
-	draftKey: string | null
+	draftKey: () => string | null
 	onRestore: (payload: TPayload) => void
 	enabled?: boolean
 }) {
@@ -17,9 +17,10 @@ export function useDraftRecovery<TPayload>(options: {
 
 	// Auto-detect draft on mount using $effect
 	$effect(() => {
-		if (!options.draftKey || options.enabled === false) return
+		const key = options.draftKey()
+		if (!key || options.enabled === false) return
 
-		const draft = loadDraft<TPayload>(options.draftKey)
+		const draft = loadDraft<TPayload>(key)
 		if (draft) {
 			showPrompt = true
 			draftTimestamp = draft.ts
@@ -43,19 +44,21 @@ export function useDraftRecovery<TPayload>(options: {
 		draftTimeText,
 
 		restore() {
-			if (!options.draftKey) return
-			const draft = loadDraft<TPayload>(options.draftKey)
+			const key = options.draftKey()
+			if (!key) return
+			const draft = loadDraft<TPayload>(key)
 			if (!draft) return
 
 			options.onRestore(draft.payload)
 			showPrompt = false
-			clearDraft(options.draftKey)
+			clearDraft(key)
 		},
 
 		dismiss() {
-			if (!options.draftKey) return
+			const key = options.draftKey()
+			if (!key) return
 			showPrompt = false
-			clearDraft(options.draftKey)
+			clearDraft(key)
 		}
 	}
 }

src/lib/admin/useFormGuards.svelte.ts

@@ -2,7 +2,9 @@ import { beforeNavigate } from '$app/navigation'
 import { toast } from '$lib/stores/toast'
 import type { AutoSaveStore } from '$lib/admin/autoSave.svelte'
 
-export function useFormGuards(autoSave: AutoSaveStore<unknown, unknown> | null) {
+export function useFormGuards<TPayload = unknown, _TResponse = unknown>(
+	autoSave: AutoSaveStore<TPayload, unknown> | null
+) {
 	if (!autoSave) return // No guards needed for create mode
 
 	// Navigation guard: flush autosave before route change
@@ -21,8 +23,12 @@ export function useFormGuards(autoSave: AutoSaveStore<unknown, unknown> | null)
 
 	// Warn before closing browser tab/window if unsaved changes
 	$effect(() => {
+		// Capture autoSave in closure to avoid non-null assertions
+		const store = autoSave
+		if (!store) return
+
 		function handleBeforeUnload(event: BeforeUnloadEvent) {
-			if (autoSave!.status !== 'saved') {
+			if (store.status !== 'saved') {
 				event.preventDefault()
 				event.returnValue = ''
 			}
@@ -34,13 +40,17 @@ export function useFormGuards(autoSave: AutoSaveStore<unknown, unknown> | null)
 
 	// Cmd/Ctrl+S keyboard shortcut for immediate save
 	$effect(() => {
+		// Capture autoSave in closure to avoid non-null assertions
+		const store = autoSave
+		if (!store) return
+
 		function handleKeydown(event: KeyboardEvent) {
 			const key = event.key.toLowerCase()
 			const isModifier = event.metaKey || event.ctrlKey
 
 			if (isModifier && key === 's') {
 				event.preventDefault()
-				autoSave!.flush().catch((error) => {
+				store.flush().catch((error) => {
 					console.error('Autosave flush failed:', error)
 					toast.error('Failed to save changes')
 				})

src/lib/components/admin/AlbumForm.svelte

@@ -46,7 +46,13 @@
 	let editorInstance = $state<{ save: () => Promise<JSONContent>; clear: () => void } | undefined>()
 	let activeTab = $state('metadata')
 	let pendingMediaIds = $state<number[]>([]) // Photos to add after album creation
-	let updatedAt = $state<string | undefined>(album?.updatedAt?.toISOString())
+	let updatedAt = $state<string | undefined>(
+		album?.updatedAt
+			? typeof album.updatedAt === 'string'
+				? album.updatedAt
+				: album.updatedAt.toISOString()
+			: undefined
+	)
 
 	const tabOptions = [
 		{ value: 'metadata', label: 'Metadata' },
@@ -98,12 +104,22 @@
 	}
 
 	// Autosave store (edit mode only)
-	const autoSave = mode === 'edit' && album
-		? createAutoSaveStore({
+	// Initialized as null and created reactively when album data becomes available
+	let autoSave = $state<ReturnType<typeof createAutoSaveStore<ReturnType<typeof buildPayload>, Album>> | null>(null)
+
+	// INITIALIZATION ORDER:
+	// 1. This effect creates autoSave when album prop becomes available
+	// 2. useFormGuards is called immediately after creation (same effect)
+	// 3. Other effects check for autoSave existence before using it
+	$effect(() => {
+		// Create autoSave when album becomes available (only once)
+		if (mode === 'edit' && album && !autoSave) {
+			const albumId = album.id // Capture album ID to avoid null reference
+			autoSave = createAutoSaveStore({
 				debounceMs: 2000,
 				getPayload: () => (hasLoaded ? buildPayload() : null),
 				save: async (payload, { signal }) => {
-					const response = await fetch(`/api/albums/${album.id}`, {
+					const response = await fetch(`/api/albums/${albumId}`, {
 						method: 'PUT',
 						headers: { 'Content-Type': 'application/json' },
 						body: JSON.stringify(payload),
@@ -114,12 +130,17 @@
 					return await response.json()
 				},
 				onSaved: (saved: Album, { prime }) => {
-					updatedAt = saved.updatedAt.toISOString()
+					updatedAt =
+						typeof saved.updatedAt === 'string' ? saved.updatedAt : saved.updatedAt.toISOString()
 					prime(buildPayload())
 					if (draftKey) clearDraft(draftKey)
 				}
 			})
-		: null
+
+			// Form guards (navigation protection, Cmd+S, beforeunload)
+			useFormGuards(autoSave)
+		}
+	})
 
 	// Draft recovery helper
 	const draftRecovery = useDraftRecovery<ReturnType<typeof buildPayload>>({
@@ -135,9 +156,6 @@
 		}
 	})
 
-	// Form guards (navigation protection, Cmd+S, beforeunload)
-	useFormGuards(autoSave)
-
 	// Watch for album changes and populate form data
 	$effect(() => {
 		if (album && mode === 'edit') {
@@ -167,6 +185,8 @@
 	})
 
 	// Trigger autosave when form data changes
+	// Using `void` operator to explicitly track dependencies without using their values
+	// This effect re-runs whenever any of these form fields change
 	$effect(() => {
 		void formData.title
 		void formData.slug
@@ -194,7 +214,8 @@
 	// Cleanup autosave on unmount
 	$effect(() => {
 		if (autoSave) {
-			return () => autoSave.destroy()
+			const instance = autoSave
+			return () => instance.destroy()
 		}
 	})