From 1070e6e9ec2915f7aa463692b97ebd1cef42384a Mon Sep 17 00:00:00 2001
From: Marcel <marcel@familienarchiv>
Date: Tue, 24 Mar 2026 11:02:38 +0100
Subject: [PATCH] feat(comments): add CommentThread, annotation panel,
 Diskussion section, and i18n keys

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 frontend/messages/de.json                     |  10 +-
 frontend/messages/en.json                     |  10 +-
 frontend/messages/es.json                     |  10 +-
 .../components/AnnotationCommentPanel.svelte  |  90 ++++
 .../src/lib/components/AnnotationLayer.svelte |  36 +-
 .../src/lib/components/CommentThread.svelte   | 394 ++++++++++++++++++
 frontend/src/lib/components/PdfViewer.svelte  |  50 ++-
 frontend/src/lib/errors.ts                    |   3 +
 .../src/routes/documents/[id]/+page.server.ts |  19 +-
 .../src/routes/documents/[id]/+page.svelte    |  35 +-
 10 files changed, 643 insertions(+), 14 deletions(-)
 create mode 100644 frontend/src/lib/components/AnnotationCommentPanel.svelte
 create mode 100644 frontend/src/lib/components/CommentThread.svelte

diff --git a/frontend/messages/de.json b/frontend/messages/de.json
index 78d24422..8d8a86c9 100644
--- a/frontend/messages/de.json
+++ b/frontend/messages/de.json
@@ -242,5 +242,13 @@
 	"admin_system_backfill_btn": "Jetzt auffüllen",
 	"admin_system_backfill_success": "{count} Dokumente wurden aufgefüllt.",
 	"comp_expandable_show_more": "Mehr anzeigen",
-	"comp_expandable_show_less": "Weniger anzeigen"
+	"comp_expandable_show_less": "Weniger anzeigen",
+	"error_comment_not_found": "Der Kommentar wurde nicht gefunden.",
+	"comment_section_title": "Diskussion",
+	"comment_placeholder": "Kommentar schreiben…",
+	"comment_btn_post": "Senden",
+	"comment_btn_reply": "Antworten",
+	"comment_edited_label": "· bearbeitet",
+	"comment_panel_title": "Kommentare",
+	"comment_panel_close": "Schließen"
 }
diff --git a/frontend/messages/en.json b/frontend/messages/en.json
index cb9f5abf..8b9fbdf5 100644
--- a/frontend/messages/en.json
+++ b/frontend/messages/en.json
@@ -242,5 +242,13 @@
 	"admin_system_backfill_btn": "Backfill now",
 	"admin_system_backfill_success": "{count} documents were backfilled.",
 	"comp_expandable_show_more": "Show more",
-	"comp_expandable_show_less": "Show less"
+	"comp_expandable_show_less": "Show less",
+	"error_comment_not_found": "The comment could not be found.",
+	"comment_section_title": "Discussion",
+	"comment_placeholder": "Write a comment…",
+	"comment_btn_post": "Send",
+	"comment_btn_reply": "Reply",
+	"comment_edited_label": "· edited",
+	"comment_panel_title": "Comments",
+	"comment_panel_close": "Close"
 }
diff --git a/frontend/messages/es.json b/frontend/messages/es.json
index 1285aacc..01d37915 100644
--- a/frontend/messages/es.json
+++ b/frontend/messages/es.json
@@ -242,5 +242,13 @@
 	"admin_system_backfill_btn": "Completar ahora",
 	"admin_system_backfill_success": "{count} documentos fueron completados.",
 	"comp_expandable_show_more": "Mostrar más",
-	"comp_expandable_show_less": "Mostrar menos"
+	"comp_expandable_show_less": "Mostrar menos",
+	"error_comment_not_found": "El comentario no pudo encontrarse.",
+	"comment_section_title": "Discusión",
+	"comment_placeholder": "Escribe un comentario…",
+	"comment_btn_post": "Enviar",
+	"comment_btn_reply": "Responder",
+	"comment_edited_label": "· editado",
+	"comment_panel_title": "Comentarios",
+	"comment_panel_close": "Cerrar"
 }
diff --git a/frontend/src/lib/components/AnnotationCommentPanel.svelte b/frontend/src/lib/components/AnnotationCommentPanel.svelte
new file mode 100644
index 00000000..b1bb59fe
--- /dev/null
+++ b/frontend/src/lib/components/AnnotationCommentPanel.svelte
@@ -0,0 +1,90 @@
+<script lang="ts">
+import CommentThread from './CommentThread.svelte';
+import { m } from '$lib/paraglide/messages.js';
+
+type Props = {
+	documentId: string;
+	annotationId: string;
+	canComment: boolean;
+	currentUserId: string | null;
+	canAdmin: boolean;
+	onClose: () => void;
+	onCountChange?: (count: number) => void;
+};
+
+let {
+	documentId,
+	annotationId,
+	canComment,
+	currentUserId,
+	canAdmin,
+	onClose,
+	onCountChange
+}: Props = $props();
+</script>
+
+<!-- Desktop / tablet panel (≥ sm): absolute overlay on the right side -->
+<div
+	class="absolute top-0 right-0 z-50 hidden h-full w-80 flex-col border-l border-brand-sand bg-white shadow-2xl sm:flex"
+>
+	<div class="flex shrink-0 items-center justify-between border-b border-brand-sand px-4 py-3">
+		<h3 class="font-sans text-xs font-bold tracking-widest text-brand-navy uppercase">
+			{m.comment_panel_title()}
+		</h3>
+		<button
+			onclick={onClose}
+			aria-label={m.comment_panel_close()}
+			class="rounded p-1 text-gray-400 transition-colors hover:bg-brand-sand/50 hover:text-brand-navy"
+		>
+			<svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+				<path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12" />
+			</svg>
+		</button>
+	</div>
+	<div class="flex-1 overflow-y-auto p-4">
+		<CommentThread
+			documentId={documentId}
+			annotationId={annotationId}
+			canComment={canComment}
+			currentUserId={currentUserId}
+			canAdmin={canAdmin}
+			loadOnMount={true}
+			onCountChange={onCountChange}
+		/>
+	</div>
+</div>
+
+<!-- Mobile modal (< sm): fixed full-screen with slide-up sheet -->
+<div class="fixed inset-0 z-50 flex flex-col sm:hidden">
+	<!-- Semi-transparent backdrop -->
+	<div class="flex-1 bg-black/40" onclick={onClose} role="presentation"></div>
+
+	<!-- Slide-up panel -->
+	<div class="flex max-h-[80vh] flex-col rounded-t-2xl bg-white shadow-2xl">
+		<div class="flex shrink-0 items-center justify-between border-b border-brand-sand px-4 py-3">
+			<h3 class="font-sans text-xs font-bold tracking-widest text-brand-navy uppercase">
+				{m.comment_panel_title()}
+			</h3>
+			<button
+				onclick={onClose}
+				aria-label={m.comment_panel_close()}
+				class="rounded p-1 text-gray-400 transition-colors hover:bg-brand-sand/50 hover:text-brand-navy"
+			>
+				<svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+					<path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12" />
+				</svg>
+			</button>
+		</div>
+		<div class="flex-1 overflow-y-auto p-4">
+			<CommentThread
+				documentId={documentId}
+				annotationId={annotationId}
+				canComment={canComment}
+				currentUserId={currentUserId}
+				canAdmin={canAdmin}
+				loadOnMount={true}
+				onCountChange={onCountChange}
+			/>
+		</div>
+	</div>
+</div>
diff --git a/frontend/src/lib/components/AnnotationLayer.svelte b/frontend/src/lib/components/AnnotationLayer.svelte
index 3a8cfae6..0321514d 100644
--- a/frontend/src/lib/components/AnnotationLayer.svelte
+++ b/frontend/src/lib/components/AnnotationLayer.svelte
@@ -23,13 +23,17 @@ let {
 	canAnnotate,
 	color,
 	onDraw,
-	onDelete
+	onDelete,
+	commentCounts,
+	onAnnotationClick
 }: {
 	annotations: Annotation[];
 	canAnnotate: boolean;
 	color: string;
 	onDraw: (rect: { x: number; y: number; width: number; height: number }) => void;
 	onDelete: (id: string) => void;
+	commentCounts?: Record<string, number>;
+	onAnnotationClick?: (id: string) => void;
 } = $props();
 
 let drawStart = $state<{ x: number; y: number } | null>(null);
@@ -112,6 +116,10 @@ const containerStyle = $derived(
 		<div
 			data-testid="annotation-{annotation.id}"
 			data-annotation
+			role="button"
+			tabindex="0"
+			onclick={() => onAnnotationClick?.(annotation.id)}
+			onkeydown={(e) => { if (e.key === 'Enter' || e.key === ' ') onAnnotationClick?.(annotation.id); }}
 			style="
 				position: absolute;
 				left: {annotation.x * 100}%;
@@ -119,7 +127,8 @@ const containerStyle = $derived(
 				width: {annotation.width * 100}%;
 				height: {annotation.height * 100}%;
 				background-color: {hexToRgba(annotation.color, 0.3)};
-				pointer-events: {canAnnotate ? 'auto' : 'none'};
+				pointer-events: auto;
+				{onAnnotationClick && !canAnnotate ? 'cursor: pointer;' : ''}
 			"
 		>
 			{#if canAnnotate}
@@ -150,6 +159,29 @@ const containerStyle = $derived(
 					">×</button
 				>
 			{/if}
+			{#if (commentCounts?.[annotation.id] ?? 0) > 0}
+				<div
+					style="
+					position: absolute;
+					bottom: -14px;
+					left: 50%;
+					transform: translateX(-50%);
+					background-color: #002850;
+					color: white;
+					font-size: 10px;
+					font-family: sans-serif;
+					padding: 1px 5px;
+					border-radius: 999px;
+					min-width: 16px;
+					text-align: center;
+					white-space: nowrap;
+					pointer-events: none;
+					line-height: 16px;
+				"
+				>
+					{commentCounts?.[annotation.id]}
+				</div>
+			{/if}
 		</div>
 	{/each}
 
diff --git a/frontend/src/lib/components/CommentThread.svelte b/frontend/src/lib/components/CommentThread.svelte
new file mode 100644
index 00000000..0e3afd7a
--- /dev/null
+++ b/frontend/src/lib/components/CommentThread.svelte
@@ -0,0 +1,394 @@
+<script lang="ts">
+import { onMount, untrack } from 'svelte';
+import { m } from '$lib/paraglide/messages.js';
+
+type CommentReply = {
+	id: string;
+	authorId: string | null;
+	authorName: string;
+	content: string;
+	createdAt: string;
+	updatedAt: string;
+};
+
+type Comment = {
+	id: string;
+	authorId: string | null;
+	authorName: string;
+	content: string;
+	createdAt: string;
+	updatedAt: string;
+	replies: CommentReply[];
+};
+
+type Props = {
+	documentId: string;
+	annotationId?: string | null;
+	initialComments?: Comment[];
+	loadOnMount?: boolean;
+	canComment: boolean;
+	currentUserId: string | null;
+	canAdmin: boolean;
+	onCountChange?: (count: number) => void;
+};
+
+let {
+	documentId,
+	annotationId = null,
+	initialComments = [],
+	loadOnMount = false,
+	canComment,
+	currentUserId,
+	canAdmin,
+	onCountChange
+}: Props = $props();
+
+let comments: Comment[] = $state(untrack(() => [...initialComments]));
+let newText: string = $state('');
+let replyingTo: string | null = $state(null);
+let replyText: string = $state('');
+let editingId: string | null = $state(null);
+let editText: string = $state('');
+let posting: boolean = $state(false);
+
+const commentsBase = $derived(
+	annotationId
+		? `/api/documents/${documentId}/annotations/${annotationId}/comments`
+		: `/api/documents/${documentId}/comments`
+);
+
+function timeAgo(iso: string): string {
+	const diff = Date.now() - new Date(iso).getTime();
+	const minutes = Math.floor(diff / 60000);
+	if (minutes < 1) return 'gerade eben';
+	if (minutes < 60) return `vor ${minutes} Minute${minutes === 1 ? '' : 'n'}`;
+	const hours = Math.floor(minutes / 60);
+	if (hours < 24) return `vor ${hours} Stunde${hours === 1 ? '' : 'n'}`;
+	const days = Math.floor(hours / 24);
+	return `vor ${days} Tag${days === 1 ? '' : 'en'}`;
+}
+
+function wasEdited(c: { createdAt: string; updatedAt: string }): boolean {
+	return c.updatedAt > c.createdAt;
+}
+
+function canModify(c: { authorId: string | null }): boolean {
+	return (currentUserId != null && c.authorId === currentUserId) || canAdmin;
+}
+
+async function reload() {
+	try {
+		const res = await fetch(commentsBase);
+		if (res.ok) {
+			comments = await res.json();
+			const total = comments.reduce((s, c) => s + 1 + c.replies.length, 0);
+			onCountChange?.(total);
+		}
+	} catch {
+		/* ignore */
+	}
+}
+
+async function postComment() {
+	const text = newText.trim();
+	if (!text || posting) return;
+	posting = true;
+	try {
+		const res = await fetch(commentsBase, {
+			method: 'POST',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify({ content: text })
+		});
+		if (res.ok) {
+			newText = '';
+			await reload();
+		}
+	} finally {
+		posting = false;
+	}
+}
+
+async function postReply(threadId: string) {
+	const text = replyText.trim();
+	if (!text || posting) return;
+	posting = true;
+	try {
+		const res = await fetch(`${commentsBase}/${threadId}/replies`, {
+			method: 'POST',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify({ content: text })
+		});
+		if (res.ok) {
+			replyText = '';
+			replyingTo = null;
+			await reload();
+		}
+	} finally {
+		posting = false;
+	}
+}
+
+async function saveEdit(commentId: string) {
+	const text = editText.trim();
+	if (!text || posting) return;
+	posting = true;
+	try {
+		const res = await fetch(`/api/documents/${documentId}/comments/${commentId}`, {
+			method: 'PATCH',
+			headers: { 'Content-Type': 'application/json' },
+			body: JSON.stringify({ content: text })
+		});
+		if (res.ok) {
+			editingId = null;
+			await reload();
+		}
+	} finally {
+		posting = false;
+	}
+}
+
+async function deleteComment(commentId: string) {
+	if (posting) return;
+	posting = true;
+	try {
+		const res = await fetch(`/api/documents/${documentId}/comments/${commentId}`, {
+			method: 'DELETE'
+		});
+		if (res.ok) {
+			await reload();
+		}
+	} finally {
+		posting = false;
+	}
+}
+
+function startEdit(comment: Comment | CommentReply) {
+	editingId = comment.id;
+	editText = comment.content;
+}
+
+function cancelEdit() {
+	editingId = null;
+	editText = '';
+}
+
+function startReply(threadId: string) {
+	replyingTo = threadId;
+	replyText = '';
+}
+
+function cancelReply() {
+	replyingTo = null;
+	replyText = '';
+}
+
+onMount(() => {
+	if (loadOnMount) {
+		reload();
+	}
+});
+</script>
+
+<div class="space-y-4">
+	{#each comments as thread, ti (thread.id)}
+		<div class={ti > 0 ? 'border-t border-brand-sand pt-4' : ''}>
+			<!-- Root comment -->
+			<div>
+				{#if editingId === thread.id}
+					<div class="flex flex-col gap-2">
+						<textarea
+							class="w-full resize-none rounded border border-brand-sand px-3 py-2 font-serif text-sm text-brand-navy focus:ring-1 focus:ring-brand-mint focus:outline-none"
+							rows={3}
+							bind:value={editText}
+						></textarea>
+						<div class="flex items-center gap-3">
+							<button
+								class="rounded bg-brand-navy px-3 py-1.5 font-sans text-xs font-medium text-white hover:bg-brand-navy/80 disabled:opacity-40"
+								disabled={posting}
+								onclick={() => saveEdit(thread.id)}
+							>
+								{m.btn_save()}
+							</button>
+							<button
+								class="font-sans text-xs text-gray-400 transition-colors hover:text-brand-navy"
+								onclick={cancelEdit}
+							>
+								{m.btn_cancel()}
+							</button>
+						</div>
+					</div>
+				{:else}
+					<div class="flex items-start justify-between gap-2">
+						<div class="min-w-0 flex-1">
+							<div class="flex flex-wrap items-center gap-2">
+								<span class="font-sans text-xs font-semibold text-brand-navy"
+									>{thread.authorName}</span
+								>
+								<span class="font-sans text-xs text-gray-400">{timeAgo(thread.createdAt)}</span>
+								{#if wasEdited(thread)}
+									<span class="font-sans text-xs text-gray-400">
+										{m.comment_edited_label()}
+										{timeAgo(thread.updatedAt)}
+									</span>
+								{/if}
+							</div>
+							<p class="mt-1 font-serif text-sm leading-relaxed text-gray-700">{thread.content}</p>
+						</div>
+						{#if canModify(thread)}
+							<div class="flex shrink-0 items-center gap-2">
+								<button
+									class="font-sans text-xs text-gray-400 transition-colors hover:text-brand-navy"
+									onclick={() => startEdit(thread)}
+								>
+									{m.btn_edit()}
+								</button>
+								<button
+									class="font-sans text-xs text-gray-400 transition-colors hover:text-brand-navy"
+									onclick={() => deleteComment(thread.id)}
+								>
+									{m.btn_delete()}
+								</button>
+							</div>
+						{/if}
+					</div>
+					<!-- Reply button on root comment only if there are no replies -->
+					{#if thread.replies.length === 0 && canComment}
+						<div class="mt-1">
+							<button
+								class="font-sans text-xs font-medium text-brand-mint transition-colors hover:text-brand-navy"
+								onclick={() => startReply(thread.id)}
+							>
+								{m.comment_btn_reply()}
+							</button>
+						</div>
+					{/if}
+				{/if}
+			</div>
+
+			<!-- Replies -->
+			{#each thread.replies as reply, ri (reply.id)}
+				<div class="mt-3 ml-6 border-l-2 border-brand-sand pl-4">
+					{#if editingId === reply.id}
+						<div class="flex flex-col gap-2">
+							<textarea
+								class="w-full resize-none rounded border border-brand-sand px-3 py-2 font-serif text-sm text-brand-navy focus:ring-1 focus:ring-brand-mint focus:outline-none"
+								rows={3}
+								bind:value={editText}
+							></textarea>
+							<div class="flex items-center gap-3">
+								<button
+									class="rounded bg-brand-navy px-3 py-1.5 font-sans text-xs font-medium text-white hover:bg-brand-navy/80 disabled:opacity-40"
+									disabled={posting}
+									onclick={() => saveEdit(reply.id)}
+								>
+									{m.btn_save()}
+								</button>
+								<button
+									class="font-sans text-xs text-gray-400 transition-colors hover:text-brand-navy"
+									onclick={cancelEdit}
+								>
+									{m.btn_cancel()}
+								</button>
+							</div>
+						</div>
+					{:else}
+						<div class="flex items-start justify-between gap-2">
+							<div class="min-w-0 flex-1">
+								<div class="flex flex-wrap items-center gap-2">
+									<span class="font-sans text-xs font-semibold text-brand-navy"
+										>{reply.authorName}</span
+									>
+									<span class="font-sans text-xs text-gray-400">{timeAgo(reply.createdAt)}</span>
+									{#if wasEdited(reply)}
+										<span class="font-sans text-xs text-gray-400">
+											{m.comment_edited_label()}
+											{timeAgo(reply.updatedAt)}
+										</span>
+									{/if}
+								</div>
+								<p class="mt-1 font-serif text-sm leading-relaxed text-gray-700">{reply.content}</p>
+							</div>
+							{#if canModify(reply)}
+								<div class="flex shrink-0 items-center gap-2">
+									<button
+										class="font-sans text-xs text-gray-400 transition-colors hover:text-brand-navy"
+										onclick={() => startEdit(reply)}
+									>
+										{m.btn_edit()}
+									</button>
+									<button
+										class="font-sans text-xs text-gray-400 transition-colors hover:text-brand-navy"
+										onclick={() => deleteComment(reply.id)}
+									>
+										{m.btn_delete()}
+									</button>
+								</div>
+							{/if}
+						</div>
+						<!-- Reply button only on the last reply -->
+						{#if ri === thread.replies.length - 1 && canComment}
+							<div class="mt-1">
+								<button
+									class="font-sans text-xs font-medium text-brand-mint transition-colors hover:text-brand-navy"
+									onclick={() => startReply(thread.id)}
+								>
+									{m.comment_btn_reply()}
+								</button>
+							</div>
+						{/if}
+					{/if}
+				</div>
+			{/each}
+
+			<!-- Reply textarea (shown when replyingTo === thread.id) -->
+			{#if replyingTo === thread.id}
+				<div class="mt-3 ml-6 flex flex-col gap-2">
+					<textarea
+						class="w-full resize-none rounded border border-brand-sand px-3 py-2 font-serif text-sm text-brand-navy focus:ring-1 focus:ring-brand-mint focus:outline-none"
+						rows={3}
+						placeholder={m.comment_placeholder()}
+						bind:value={replyText}
+					></textarea>
+					<div class="flex items-center gap-3">
+						<button
+							class="rounded bg-brand-navy px-3 py-1.5 font-sans text-xs font-medium text-white hover:bg-brand-navy/80 disabled:opacity-40"
+							disabled={posting}
+							onclick={() => postReply(thread.id)}
+						>
+							{m.comment_btn_post()}
+						</button>
+						<button
+							class="font-sans text-xs text-gray-400 transition-colors hover:text-brand-navy"
+							onclick={cancelReply}
+						>
+							{m.btn_cancel()}
+						</button>
+					</div>
+				</div>
+			{/if}
+		</div>
+	{/each}
+
+	<!-- New top-level comment textarea -->
+	{#if canComment}
+		<div class={comments.length > 0 ? 'border-t border-brand-sand pt-4' : ''}>
+			<div class="flex flex-col gap-2">
+				<textarea
+					class="w-full resize-none rounded border border-brand-sand px-3 py-2 font-serif text-sm text-brand-navy focus:ring-1 focus:ring-brand-mint focus:outline-none"
+					rows={3}
+					placeholder={m.comment_placeholder()}
+					bind:value={newText}
+				></textarea>
+				<div>
+					<button
+						class="rounded bg-brand-navy px-3 py-1.5 font-sans text-xs font-medium text-white hover:bg-brand-navy/80 disabled:opacity-40"
+						disabled={posting || !newText.trim()}
+						onclick={postComment}
+					>
+						{m.comment_btn_post()}
+					</button>
+				</div>
+			</div>
+		</div>
+	{/if}
+</div>
diff --git a/frontend/src/lib/components/PdfViewer.svelte b/frontend/src/lib/components/PdfViewer.svelte
index 7863143c..fc27684d 100644
--- a/frontend/src/lib/components/PdfViewer.svelte
+++ b/frontend/src/lib/components/PdfViewer.svelte
@@ -1,16 +1,24 @@
 <script lang="ts">
 import { onMount } from 'svelte';
+import { SvelteMap } from 'svelte/reactivity';
 import type { PDFDocumentProxy, PDFPageProxy, RenderTask } from 'pdfjs-dist';
 import AnnotationLayer from './AnnotationLayer.svelte';
+import AnnotationCommentPanel from './AnnotationCommentPanel.svelte';
 
 let {
 	url,
 	documentId = '',
-	canAnnotate = false
+	canAnnotate = false,
+	canComment,
+	currentUserId,
+	canAdmin
 }: {
 	url: string;
 	documentId?: string;
 	canAnnotate?: boolean;
+	canComment?: boolean;
+	currentUserId?: string | null;
+	canAdmin?: boolean;
 } = $props();
 
 let pdfDoc = $state<PDFDocumentProxy | null>(null);
@@ -48,6 +56,8 @@ type Annotation = {
 let annotations = $state<Annotation[]>([]);
 let annotateMode = $state(false);
 let annotateColor = $state('#ffff00');
+let commentCounts = new SvelteMap<string, number>();
+let activeAnnotationId = $state<string | null>(null);
 
 onMount(async () => {
 	// Dynamic import keeps pdfjs out of the SSR bundle entirely
@@ -159,11 +169,31 @@ async function prerender(doc: PDFDocumentProxy, pageNum: number) {
 	}
 }
 
+async function loadCommentCounts(docId: string, anns: Annotation[]) {
+	await Promise.all(
+		anns.map(async (a) => {
+			try {
+				const res = await fetch(`/api/documents/${docId}/annotations/${a.id}/comments`);
+				if (res.ok) {
+					const threads = (await res.json()) as Array<{ replies: unknown[] }>;
+					const total = threads.reduce((sum, t) => sum + 1 + t.replies.length, 0);
+					commentCounts.set(a.id, total);
+				}
+			} catch {
+				// ignore
+			}
+		})
+	);
+}
+
 async function loadAnnotations(docId: string) {
 	if (!docId) return;
 	try {
 		const res = await fetch(`/api/documents/${docId}/annotations`);
-		if (res.ok) annotations = await res.json();
+		if (res.ok) {
+			annotations = await res.json();
+			await loadCommentCounts(docId, annotations);
+		}
 	} catch {
 		// ignore
 	}
@@ -413,10 +443,26 @@ function zoomOut() {
 							color={annotateColor}
 							onDraw={handleAnnotationDraw}
 							onDelete={handleAnnotationDelete}
+							commentCounts={Object.fromEntries(commentCounts)}
+							onAnnotationClick={(id) => (activeAnnotationId = id)}
 						/>
 					</div>
 				</div>
 			{/if}
 		</div>
+
+		{#if activeAnnotationId}
+			<AnnotationCommentPanel
+				documentId={documentId}
+				annotationId={activeAnnotationId}
+				canComment={canComment ?? false}
+				currentUserId={currentUserId ?? null}
+				canAdmin={canAdmin ?? false}
+				onClose={() => (activeAnnotationId = null)}
+				onCountChange={(count) => {
+					if (activeAnnotationId) commentCounts.set(activeAnnotationId, count);
+				}}
+			/>
+		{/if}
 	</div>
 {/if}
diff --git a/frontend/src/lib/errors.ts b/frontend/src/lib/errors.ts
index 5df07506..3e679fbc 100644
--- a/frontend/src/lib/errors.ts
+++ b/frontend/src/lib/errors.ts
@@ -16,6 +16,7 @@ export type ErrorCode =
 	| 'INVALID_RESET_TOKEN'
 	| 'ANNOTATION_NOT_FOUND'
 	| 'ANNOTATION_OVERLAP'
+	| 'COMMENT_NOT_FOUND'
 	| 'UNAUTHORIZED'
 	| 'FORBIDDEN'
 	| 'VALIDATION_ERROR'
@@ -67,6 +68,8 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 			return m.error_annotation_not_found();
 		case 'ANNOTATION_OVERLAP':
 			return m.error_annotation_overlap();
+		case 'COMMENT_NOT_FOUND':
+			return m.error_comment_not_found();
 		case 'UNAUTHORIZED':
 			return m.error_unauthorized();
 		case 'FORBIDDEN':
diff --git a/frontend/src/routes/documents/[id]/+page.server.ts b/frontend/src/routes/documents/[id]/+page.server.ts
index 286d9fbc..dce5f89f 100644
--- a/frontend/src/routes/documents/[id]/+page.server.ts
+++ b/frontend/src/routes/documents/[id]/+page.server.ts
@@ -1,19 +1,26 @@
 import { error, redirect } from '@sveltejs/kit';
+import { env } from '$env/dynamic/private';
 import { createApiClient } from '$lib/api.server';
 import { getErrorMessage } from '$lib/errors';
 
 export async function load({ params, fetch }) {
 	const { id } = params;
 	const api = createApiClient(fetch);
+	const base = env.API_INTERNAL_URL || 'http://localhost:8080';
 
-	const result = await api.GET('/api/documents/{id}', { params: { path: { id } } });
+	const [docResult, commentsRes] = await Promise.all([
+		api.GET('/api/documents/{id}', { params: { path: { id } } }),
+		fetch(`${base}/api/documents/${id}/comments`)
+	]);
 
-	if (result.response.status === 401) throw redirect(302, '/login');
+	if (docResult.response.status === 401) throw redirect(302, '/login');
 
-	if (!result.response.ok) {
-		const code = (result.error as unknown as { code?: string })?.code;
-		throw error(result.response.status, getErrorMessage(code));
+	if (!docResult.response.ok) {
+		const code = (docResult.error as unknown as { code?: string })?.code;
+		throw error(docResult.response.status, getErrorMessage(code));
 	}
 
-	return { document: result.data! };
+	const comments = commentsRes.ok ? await commentsRes.json() : [];
+
+	return { document: docResult.data!, comments };
 }
diff --git a/frontend/src/routes/documents/[id]/+page.svelte b/frontend/src/routes/documents/[id]/+page.svelte
index 7716b311..2ec4747c 100644
--- a/frontend/src/routes/documents/[id]/+page.svelte
+++ b/frontend/src/routes/documents/[id]/+page.svelte
@@ -4,10 +4,18 @@ import { formatDate } from '$lib/utils/date';
 import { diffWords } from 'diff';
 import ExpandableText from '$lib/components/ExpandableText.svelte';
 import PdfViewer from '$lib/components/PdfViewer.svelte';
+import CommentThread from '$lib/components/CommentThread.svelte';
 
 let { data } = $props();
 
 const doc = $derived(data.document);
+const canComment = $derived((data.canAnnotate || data.canWrite) ?? false);
+const canAdmin = $derived(
+	(data.user?.groups as Array<{ permissions: string[] }> | undefined)?.some((g) =>
+		g.permissions.includes('ADMIN')
+	) ?? false
+);
+const currentUserId = $derived((data.user?.id as string | undefined) ?? null);
 
 let fileUrl = $state('');
 let isLoading = $state(false);
@@ -821,6 +829,24 @@ function versionLabel(v: VersionSummary, index: number): string {
 					{/if}
 				</div>
 
+				<!-- 5. DISKUSSION -->
+				<div>
+					<div class="border-b border-brand-sand pb-2">
+						<h3 class="font-sans text-xs font-bold tracking-widest text-brand-navy uppercase">
+							{m.comment_section_title()}
+						</h3>
+					</div>
+					<div class="mt-4">
+						<CommentThread
+							documentId={doc.id}
+							initialComments={data.comments ?? []}
+							canComment={canComment}
+							currentUserId={currentUserId}
+							canAdmin={canAdmin}
+						/>
+					</div>
+				</div>
+
 				<!-- Footer -->
 				<div class="border-t border-brand-sand pt-4 font-sans text-[10px] text-gray-400">
 					<p class="truncate">ID: {doc.id}</p>
@@ -875,7 +901,14 @@ function versionLabel(v: VersionSummary, index: number): string {
 					<p class="font-sans text-sm tracking-wide uppercase">{m.doc_no_scan()}</p>
 				</div>
 			{:else if fileUrl && doc.contentType?.startsWith('application/pdf')}
-				<PdfViewer url={fileUrl} documentId={doc.id} canAnnotate={data.canAnnotate} />
+				<PdfViewer
+					url={fileUrl}
+					documentId={doc.id}
+					canAnnotate={data.canAnnotate}
+					canComment={canComment}
+					currentUserId={currentUserId}
+					canAdmin={canAdmin}
+				/>
 			{:else if fileUrl}
 				<div class="flex h-full w-full items-center justify-center overflow-auto p-8">
 					<img