feat(frontend): implement file selection with long-press, shift+click, and touch drag

- selection.ts: store with select/deselect/toggle/enter/exit, derived count and active
- FileCard: long-press (400ms) enters selection mode, shows check overlay, blocks context menu
- Header: Select/Cancel button toggles selection mode
- SelectionBar: floating bar above navbar with count, Edit tags, Add to pool, Delete
- Shift+click range-selects between last and current index (desktop)
- Touch drag-to-select/deselect after long-press; non-passive touchmove blocks scroll only during drag

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/file/FileCard.svelte

@@ -3,12 +3,27 @@
 	import { authStore } from '$lib/stores/auth';
 	import type { File } from '$lib/api/types';
 
+	const LONG_PRESS_MS = 400;
+	const DRAG_THRESHOLD = 8; // px — cancel long-press if pointer moves more than this
+
 	interface Props {
 		file: File;
-		onclick?: (file: File) => void;
+		index: number;
+		selected?: boolean;
+		selectionMode?: boolean;
+		onTap?: (e: MouseEvent) => void;
+		/** Called when long-press fires; receives the pointerType of the gesture. */
+		onLongPress?: (pointerType: string) => void;
 	}
 
-	let { file, onclick }: Props = $props();
+	let {
+		file,
+		index,
+		selected = false,
+		selectionMode = false,
+		onTap,
+		onLongPress,
+	}: Props = $props();
 
 	let imgSrc = $state<string | null>(null);
 	let failed = $state(false);
@@ -40,8 +55,51 @@
 		};
 	});
 
-	function handleClick() {
-		onclick?.(file);
+	// --- Long press + drag detection ---
+	let pressTimer: ReturnType<typeof setTimeout> | null = null;
+	let didLongPress = false;
+	let pressStartX = 0;
+	let pressStartY = 0;
+	let currentPointerType = '';
+
+	function onPointerDown(e: PointerEvent) {
+		if (e.button !== 0 && e.pointerType === 'mouse') return;
+		didLongPress = false;
+		pressStartX = e.clientX;
+		pressStartY = e.clientY;
+		currentPointerType = e.pointerType;
+		pressTimer = setTimeout(() => {
+			didLongPress = true;
+			onLongPress?.(currentPointerType);
+		}, LONG_PRESS_MS);
+	}
+
+	function onPointerMoveInternal(e: PointerEvent) {
+		// Cancel long-press if pointer has moved significantly (user is scrolling)
+		if (pressTimer !== null) {
+			const dx = e.clientX - pressStartX;
+			const dy = e.clientY - pressStartY;
+			if (Math.hypot(dx, dy) > DRAG_THRESHOLD) {
+				clearTimeout(pressTimer);
+				pressTimer = null;
+			}
+		}
+	}
+
+	function cancelPress() {
+		if (pressTimer !== null) {
+			clearTimeout(pressTimer);
+			pressTimer = null;
+		}
+	}
+
+	function onClick(e: MouseEvent) {
+		if (didLongPress) {
+			didLongPress = false;
+			return;
+		}
+		cancelPress();
+		onTap?.(e);
 	}
 </script>
 
@@ -49,17 +107,38 @@
 <div
 	class="card"
 	class:loaded={!!imgSrc}
-	onclick={handleClick}
+	class:selected
+	data-file-index={index}
+	onpointerdown={onPointerDown}
+	onpointermove={onPointerMoveInternal}
+	onpointerup={() => { cancelPress(); didLongPress = false; }}
+	onpointerleave={cancelPress}
+	oncontextmenu={(e) => e.preventDefault()}
+	onclick={onClick}
 	title={file.original_name ?? undefined}
 >
 	{#if imgSrc}
-		<img src={imgSrc} alt={file.original_name ?? ''} class="thumb" />
+		<img src={imgSrc} alt={file.original_name ?? ''} class="thumb" draggable="false" />
 	{:else if failed}
 		<div class="placeholder failed" aria-label="Failed to load"></div>
 	{:else}
 		<div class="placeholder loading" aria-label="Loading"></div>
 	{/if}
 	<div class="overlay"></div>
+	{#if selected}
+		<div class="check" aria-hidden="true">
+			<svg width="18" height="18" viewBox="0 0 18 18" fill="none">
+				<circle cx="9" cy="9" r="8.5" fill="rgba(0,0,0,0.55)" stroke="white" stroke-width="1"/>
+				<path d="M5 9l3 3 5-5" stroke="white" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round"/>
+			</svg>
+		</div>
+	{:else if selectionMode}
+		<div class="check" aria-hidden="true">
+			<svg width="18" height="18" viewBox="0 0 18 18" fill="none">
+				<circle cx="9" cy="9" r="8.5" fill="rgba(0,0,0,0.35)" stroke="rgba(255,255,255,0.5)" stroke-width="1"/>
+			</svg>
+		</div>
+	{/if}
 </div>
 
 <style>
@@ -73,6 +152,8 @@
 		cursor: pointer;
 		background-color: var(--color-bg-elevated);
 		flex-shrink: 0;
+		user-select: none;
+		-webkit-user-select: none;
 	}
 
 	.thumb {
@@ -114,6 +195,17 @@
 		background-color: rgba(0, 0, 0, 0.3);
 	}
 
+	.card.selected .overlay {
+		background-color: color-mix(in srgb, var(--color-accent) 35%, transparent);
+	}
+
+	.check {
+		position: absolute;
+		top: 6px;
+		right: 6px;
+		pointer-events: none;
+	}
+
 	@keyframes shimmer {
 		0% { background-position: 200% 0; }
 		100% { background-position: -200% 0; }

frontend/src/lib/components/layout/Header.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
-	import type { FileSortField, SortOrder } from '$lib/stores/sorting';
+	import type { SortOrder } from '$lib/stores/sorting';
+	import { selectionStore, selectionActive } from '$lib/stores/selection';
 
 	interface Props {
 		sortOptions: { value: string; label: string }[];
@@ -23,6 +24,14 @@
 </script>
 
 <header>
+	<button
+		class="select-btn"
+		class:active={$selectionActive}
+		onclick={() => ($selectionActive ? selectionStore.exit() : selectionStore.enter())}
+	>
+		{$selectionActive ? 'Cancel' : 'Select'}
+	</button>
+
 	<div class="controls">
 		<select
 			class="sort-select"
@@ -70,6 +79,29 @@
 		flex-shrink: 0;
 	}
 
+	.select-btn {
+		height: 30px;
+		padding: 0 12px;
+		border-radius: 6px;
+		border: 1px solid color-mix(in srgb, var(--color-accent) 30%, transparent);
+		background-color: var(--color-bg-elevated);
+		color: var(--color-text-muted);
+		font-size: 0.85rem;
+		font-family: inherit;
+		cursor: pointer;
+	}
+
+	.select-btn:hover {
+		color: var(--color-text-primary);
+		border-color: var(--color-accent);
+	}
+
+	.select-btn.active {
+		background-color: color-mix(in srgb, var(--color-accent) 25%, var(--color-bg-elevated));
+		color: var(--color-accent);
+		border-color: var(--color-accent);
+	}
+
 	.controls {
 		display: flex;
 		align-items: center;

frontend/src/lib/components/layout/SelectionBar.svelte

@@ -0,0 +1,138 @@
+<script lang="ts">
+	import { selectionStore, selectionCount } from '$lib/stores/selection';
+
+	interface Props {
+		onEditTags: () => void;
+		onAddToPool: () => void;
+		onDelete: () => void;
+	}
+
+	let { onEditTags, onAddToPool, onDelete }: Props = $props();
+
+	function handleKeydown(e: KeyboardEvent) {
+		if (e.key === 'Escape') selectionStore.exit();
+	}
+</script>
+
+<svelte:window onkeydown={handleKeydown} />
+
+<div class="bar" role="toolbar" aria-label="Selection actions">
+	<div class="row">
+		<!-- Count / deselect all -->
+		<button class="count" onclick={() => selectionStore.exit()} title="Clear selection">
+			<span class="num">{$selectionCount}</span>
+			<span class="label">selected</span>
+			<svg class="close-icon" width="14" height="14" viewBox="0 0 14 14" fill="none" aria-hidden="true">
+				<path d="M2 2l10 10M12 2L2 12" stroke="currentColor" stroke-width="1.8" stroke-linecap="round"/>
+			</svg>
+		</button>
+
+		<div class="spacer"></div>
+
+		<button class="action edit-tags" onclick={onEditTags}>Edit tags</button>
+		<button class="action add-pool" onclick={onAddToPool}>Add to pool</button>
+		<button class="action delete" onclick={onDelete}>Delete</button>
+	</div>
+</div>
+
+<style>
+	.bar {
+		position: fixed;
+		left: 10px;
+		right: 10px;
+		bottom: 65px;
+		box-sizing: border-box;
+		background-color: var(--color-bg-secondary);
+		border-radius: 10px;
+		box-shadow: 0 0 12px rgba(0, 0, 0, 0.5);
+		padding: 12px 14px;
+		z-index: 100;
+		animation: slide-up 0.18s ease-out;
+	}
+
+	@keyframes slide-up {
+		from { transform: translateY(12px); opacity: 0; }
+		to   { transform: translateY(0);    opacity: 1; }
+	}
+
+	.row {
+		display: flex;
+		align-items: center;
+		gap: 4px;
+	}
+
+	.spacer {
+		flex: 1;
+	}
+
+	.count {
+		display: flex;
+		align-items: center;
+		gap: 5px;
+		background: none;
+		border: none;
+		cursor: pointer;
+		padding: 4px 6px;
+		border-radius: 6px;
+		color: var(--color-text-muted);
+		font-family: inherit;
+	}
+
+	.count:hover {
+		background-color: color-mix(in srgb, var(--color-accent) 12%, transparent);
+		color: var(--color-text-primary);
+	}
+
+	.num {
+		font-size: 1.1rem;
+		font-weight: 700;
+		color: var(--color-text-primary);
+	}
+
+	.label {
+		font-size: 0.85rem;
+	}
+
+	.close-icon {
+		opacity: 0.5;
+	}
+
+	.count:hover .close-icon {
+		opacity: 1;
+	}
+
+	.action {
+		background: none;
+		border: none;
+		cursor: pointer;
+		padding: 6px 10px;
+		border-radius: 6px;
+		font-size: 0.85rem;
+		font-family: inherit;
+		font-weight: 600;
+	}
+
+	.edit-tags {
+		color: var(--color-info);
+	}
+
+	.edit-tags:hover {
+		background-color: color-mix(in srgb, var(--color-info) 15%, transparent);
+	}
+
+	.add-pool {
+		color: var(--color-warning);
+	}
+
+	.add-pool:hover {
+		background-color: color-mix(in srgb, var(--color-warning) 15%, transparent);
+	}
+
+	.delete {
+		color: var(--color-danger);
+	}
+
+	.delete:hover {
+		background-color: color-mix(in srgb, var(--color-danger) 15%, transparent);
+	}
+</style>

frontend/src/lib/stores/selection.ts

@@ -0,0 +1,65 @@
+import { writable, derived } from 'svelte/store';
+
+interface SelectionState {
+	active: boolean;
+	ids: Set<string>;
+}
+
+function createSelectionStore() {
+	const { subscribe, update, set } = writable<SelectionState>({
+		active: false,
+		ids: new Set(),
+	});
+
+	return {
+		subscribe,
+
+		enter() {
+			update((s) => ({ ...s, active: true }));
+		},
+
+		exit() {
+			set({ active: false, ids: new Set() });
+		},
+
+		toggle(id: string) {
+			update((s) => {
+				const ids = new Set(s.ids);
+				if (ids.has(id)) {
+					ids.delete(id);
+				} else {
+					ids.add(id);
+				}
+				// Exit selection mode automatically when last item is deselected
+				const active = ids.size > 0;
+				return { active, ids };
+			});
+		},
+
+		select(id: string) {
+			update((s) => {
+				const ids = new Set(s.ids);
+				ids.add(id);
+				return { active: true, ids };
+			});
+		},
+
+		deselect(id: string) {
+			update((s) => {
+				const ids = new Set(s.ids);
+				ids.delete(id);
+				const active = ids.size > 0;
+				return { active, ids };
+			});
+		},
+
+		clear() {
+			set({ active: false, ids: new Set() });
+		},
+	};
+}
+
+export const selectionStore = createSelectionStore();
+
+export const selectionCount = derived(selectionStore, ($s) => $s.ids.size);
+export const selectionActive = derived(selectionStore, ($s) => $s.active);

frontend/src/routes/files/+page.svelte

@@ -6,8 +6,10 @@
 	import FileCard from '$lib/components/file/FileCard.svelte';
 	import FilterBar from '$lib/components/file/FilterBar.svelte';
 	import Header from '$lib/components/layout/Header.svelte';
+	import SelectionBar from '$lib/components/layout/SelectionBar.svelte';
 	import InfiniteScroll from '$lib/components/common/InfiniteScroll.svelte';
 	import { fileSorting, type FileSortField } from '$lib/stores/sorting';
+	import { selectionStore, selectionActive } from '$lib/stores/selection';
 	import { parseDslFilter } from '$lib/utils/dsl';
 	import type { File, FileCursorPage } from '$lib/api/types';
 
@@ -27,14 +29,10 @@
 	let error = $state('');
 	let filterOpen = $state(false);
 
-	// Derive current filter from URL ?filter= param
 	let filterParam = $derived($page.url.searchParams.get('filter'));
 	let activeTokens = $derived(parseDslFilter(filterParam));
-
-	// Track sort/order from store
 	let sortState = $derived($fileSorting);
 
-	// Reset + reload whenever sort or filter changes
 	let resetKey = $derived(`${sortState.sort}|${sortState.order}|${filterParam ?? ''}`);
 	let prevKey = $state('');
 
@@ -52,7 +50,6 @@
 		if (loading || !hasMore) return;
 		loading = true;
 		error = '';
-
 		try {
 			const params = new URLSearchParams({
 				limit: String(LIMIT),
@@ -61,7 +58,6 @@
 			});
 			if (nextCursor) params.set('cursor', nextCursor);
 			if (filterParam) params.set('filter', filterParam);
-
 			const res = await api.get<FileCursorPage>(`/files?${params}`);
 			files = [...files, ...(res.items ?? [])];
 			nextCursor = res.next_cursor ?? null;
@@ -84,6 +80,90 @@
 		goto(url.toString(), { replaceState: true });
 		filterOpen = false;
 	}
+
+	function openFile(file: File) {
+		if (file.id) goto(`/files/${file.id}`);
+	}
+
+	// ---- Selection logic ----
+
+	let lastSelectedIdx = $state<number | null>(null);
+
+	function handleTap(file: File, idx: number, e: MouseEvent) {
+		if (!$selectionActive) {
+			openFile(file);
+			return;
+		}
+		if (e.shiftKey && lastSelectedIdx !== null) {
+			// Range-select between lastSelectedIdx and idx (desktop)
+			const from = Math.min(lastSelectedIdx, idx);
+			const to = Math.max(lastSelectedIdx, idx);
+			for (let i = from; i <= to; i++) {
+				if (files[i]?.id) selectionStore.select(files[i].id!);
+			}
+			lastSelectedIdx = idx;
+		} else {
+			if (file.id) selectionStore.toggle(file.id);
+			lastSelectedIdx = idx;
+		}
+	}
+
+	function handleLongPress(file: File, idx: number, pointerType: string) {
+		// Determine drag mode from whether this card is already selected
+		const alreadySelected = $selectionStore.ids.has(file.id!);
+		if (alreadySelected) {
+			selectionStore.deselect(file.id!);
+			dragMode = 'deselect';
+		} else {
+			selectionStore.select(file.id!);
+			dragMode = 'select';
+		}
+		lastSelectedIdx = idx;
+		// Only enter drag-select for touch — shift+click covers desktop range selection
+		if (pointerType === 'touch') dragSelecting = true;
+	}
+
+	// ---- Drag-to-select / deselect (touch only) ----
+	// Entered only after a long-press (400ms stillness), so by the time we
+	// add the touchmove listener the scroll gesture hasn't started yet.
+	// A non-passive touchmove listener lets us call preventDefault() to block
+	// scroll while the user slides their finger across cards.
+
+	let dragSelecting = $state(false);
+	let dragMode = $state<'select' | 'deselect'>('select');
+
+	$effect(() => {
+		if (!dragSelecting) return;
+
+		function onTouchMove(e: TouchEvent) {
+			e.preventDefault(); // block scroll while drag-selecting
+			const touch = e.touches[0];
+			const el = document.elementFromPoint(touch.clientX, touch.clientY);
+			const card = el?.closest<HTMLElement>('[data-file-index]');
+			if (!card) return;
+			const idx = parseInt(card.dataset.fileIndex ?? '');
+			if (isNaN(idx) || !files[idx]?.id) return;
+			if (dragMode === 'select') {
+				selectionStore.select(files[idx].id!);
+			} else {
+				selectionStore.deselect(files[idx].id!);
+			}
+			lastSelectedIdx = idx;
+		}
+
+		function onTouchEnd() {
+			dragSelecting = false;
+		}
+
+		document.addEventListener('touchmove', onTouchMove, { passive: false });
+		document.addEventListener('touchend', onTouchEnd);
+		document.addEventListener('touchcancel', onTouchEnd);
+		return () => {
+			document.removeEventListener('touchmove', onTouchMove);
+			document.removeEventListener('touchend', onTouchEnd);
+			document.removeEventListener('touchcancel', onTouchEnd);
+		};
+	});
 </script>
 
 <svelte:head>
@@ -115,8 +195,15 @@
 		{/if}
 
 		<div class="grid">
-			{#each files as file (file.id)}
-				<FileCard {file} />
+			{#each files as file, i (file.id)}
+				<FileCard
+					{file}
+					index={i}
+					selected={$selectionStore.ids.has(file.id ?? '')}
+					selectionMode={$selectionActive}
+					onTap={(e) => handleTap(file, i, e)}
+					onLongPress={(pt) => handleLongPress(file, i, pt)}
+				/>
 			{/each}
 		</div>
 
@@ -128,6 +215,19 @@
 	</main>
 </div>
 
+{#if $selectionActive}
+	<SelectionBar
+		onEditTags={() => {/* TODO */}}
+		onAddToPool={() => {/* TODO */}}
+		onDelete={() => {
+			if (confirm(`Delete ${$selectionStore.ids.size} file(s)?`)) {
+				// TODO: call delete API
+				selectionStore.exit();
+			}
+		}}
+	/>
+{/if}
+
 <style>
 	.page {
 		flex: 1;