diff --git a/client-next/public/robots.txt b/client-next/public/robots.txt
deleted file mode 100644
index 9f7d44f..0000000
--- a/client-next/public/robots.txt
+++ /dev/null
@@ -1,3 +0,0 @@
-User-agent: *
-Allow: /
-Sitemap: https://postscholar.org/sitemap.xml
diff --git a/client-next/scripts/generate-sitemap.js b/client-next/scripts/generate-sitemap.js
index ba1c188..6a2713f 100644
--- a/client-next/scripts/generate-sitemap.js
+++ b/client-next/scripts/generate-sitemap.js
@@ -1,5 +1,5 @@
-// Sitemap generator for PostScholar
-// Run manually after deployment to update sitemap.xml
+// Legacy sitemap generator — prefer client-next/src/app/sitemap.js (dynamic).
+// This script remains for one-off exports if the API is unavailable.
 // Usage: DATABASE_URL=your_railway_public_url node client-next/scripts/generate-sitemap.js
 
 const { Pool } = require('pg')
@@ -10,12 +10,24 @@ const pool = new Pool({ connectionString: process.env.DATABASE_URL })
 
 async function generateSitemap() {
   const result = await pool.query(
-    'SELECT id, created_at FROM discussions ORDER BY created_at DESC'
+    `SELECT d.id, d.created_at, p.title
+     FROM discussions d
+     JOIN papers p ON p.id = d.paper_id
+     ORDER BY d.created_at DESC`
   )
 
+  function slugify(title, id) {
+    const slug = (title || 'discussion')
+      .toLowerCase()
+      .replace(/[^a-z0-9]+/g, '-')
+      .replace(/^-+|-+$/g, '')
+      .slice(0, 80)
+    return `${slug || 'discussion'}-${id}`
+  }
+
   const urls = result.rows.map(row => `
   <url>
-    <loc>https://postscholar.org/d/${row.id}</loc>
+    <loc>https://postscholar.org/d/${slugify(row.title, row.id)}</loc>
     <lastmod>${new Date(row.created_at).toISOString().split('T')[0]}</lastmod>
     <changefreq>weekly</changefreq>
     <priority>0.8</priority>
diff --git a/client-next/src/app/LandingHome.jsx b/client-next/src/app/LandingHome.jsx
index 07379ee..d1b4349 100644
--- a/client-next/src/app/LandingHome.jsx
+++ b/client-next/src/app/LandingHome.jsx
@@ -1,4 +1,5 @@
 import Link from 'next/link'
+import { discussionPath } from '@/lib/discussionSlug'
 import Layout from '@/components/Layout'
 import styles from './landing.module.css'
 
@@ -101,7 +102,11 @@ export default function LandingHome({ discussions = [] }) {
             ) : (
               <div className={styles.discussionList}>
                 {preview.map(d => (
-                  <Link key={d.id} href={`/d/${d.id}`} className={styles.discussionItem}>
+                  <Link
+                    key={d.id}
+                    href={discussionPath({ id: d.id, title: d.title })}
+                    className={styles.discussionItem}
+                  >
                     <h3 className={`${styles.discussionTitle} paper-title`}>{d.title}</h3>
                     <p className={styles.discussionMeta}>
                       {[d.username || d.started_by, formatAuthors(d.authors_json), d.journal, d.year]
diff --git a/client-next/src/app/d/[id]/page.js b/client-next/src/app/d/[id]/page.js
deleted file mode 100644
index 02ee9be..0000000
--- a/client-next/src/app/d/[id]/page.js
+++ /dev/null
@@ -1,88 +0,0 @@
-import Link from 'next/link'
-import Layout from '@/components/Layout'
-import PaperHeader from '@/components/PaperHeader'
-import PaperSidebar from '@/components/PaperSidebar'
-import DiscussionComments from './DiscussionComments'
-import { getServerApiUrl } from '@/lib/config'
-import styles from './Discussion.module.css'
-
-async function getDiscussionData(id) {
-  try {
-    const res = await fetch(`${getServerApiUrl()}/discussions/${id}/paper`, {
-      cache: 'no-store'
-    })
-    if (!res.ok) return null
-    return res.json()
-  } catch (error) {
-    console.error('Failed to fetch discussion data:', error)
-    return null
-  }
-}
-
-export async function generateMetadata({ params }) {
-  const { id } = await params
-  const data = await getDiscussionData(id)
-  if (!data || data.error) {
-    return {
-      title: 'Discussion — PostScholar',
-      description: 'Academic discussion on PostScholar'
-    }
-  }
-
-  const { paper } = data
-  const authors = paper.authors_json?.map(a => `${a.given} ${a.family}`).join(', ') || ''
-  const title = paper.title ? `${paper.title} — PostScholar` : 'Discussion — PostScholar'
-  const description = paper.abstract
-    ? paper.abstract.slice(0, 160)
-    : `Discussion of "${paper.title}" on PostScholar`
-
-  return {
-    title,
-    description,
-    openGraph: {
-      title: paper.title,
-      description: paper.abstract?.slice(0, 200) || description,
-      type: 'article',
-      authors: authors ? [authors] : undefined,
-    },
-    twitter: {
-      card: 'summary',
-      title: paper.title,
-      description: paper.abstract?.slice(0, 200) || description,
-    },
-  }
-}
-
-export default async function DiscussionPage({ params }) {
-  const { id } = await params
-  const data = await getDiscussionData(id)
-
-  if (!data || data.error) {
-    return (
-      <Layout>
-        <p className={styles.error}>Discussion not found.</p>
-      </Layout>
-    )
-  }
-
-  const { paper, started_by, discussion_created_at, custom_tags } = data
-
-  const sidebar = paper ? <PaperSidebar paper={paper} discussionId={id} /> : null
-
-  return (
-    <Layout sidebar={sidebar}>
-      <Link href="/explore" className="backLink">← Discussions</Link>
-      {paper && (
-        <PaperHeader
-          paper={paper}
-          startedBy={started_by}
-          discussionCreatedAt={discussion_created_at}
-          customTags={custom_tags || []}
-          discussionId={id}
-        />
-      )}
-      <div className={styles.divider} />
-      <DiscussionComments discussionId={id} />
-    </Layout>
-  )
-}
\ No newline at end of file
diff --git a/client-next/src/app/d/[slug]/page.js b/client-next/src/app/d/[slug]/page.js
new file mode 100644
index 0000000..7a18361
--- /dev/null
+++ b/client-next/src/app/d/[slug]/page.js
@@ -0,0 +1,194 @@
+import Link from 'next/link'
+import { redirect } from 'next/navigation'
+import Layout from '@/components/Layout'
+import PaperHeader from '@/components/PaperHeader'
+import PaperSidebar from '@/components/PaperSidebar'
+import DiscussionComments from '../[id]/DiscussionComments'
+import { getServerApiUrl } from '@/lib/config'
+import {
+  buildDiscussionSlug,
+  parseDiscussionId,
+} from '@/lib/discussionSlug'
+import { SITE_NAME, SITE_URL } from '@/lib/site'
+import styles from '../[id]/Discussion.module.css'
+
+async function getDiscussionData(id) {
+  try {
+    const res = await fetch(`${getServerApiUrl()}/discussions/${id}/paper`, {
+      cache: 'no-store',
+    })
+    if (!res.ok) return null
+    return res.json()
+  } catch (error) {
+    console.error('Failed to fetch discussion data:', error)
+    return null
+  }
+}
+
+function buildJsonLd({ paper, discussionId, startedBy, discussionCreatedAt }) {
+  const authors = paper.authors_json?.map(a => ({
+    '@type': 'Person',
+    name: [a.given, a.family].filter(Boolean).join(' '),
+  })) || []
+
+  const pageUrl = `${SITE_URL}/d/${buildDiscussionSlug(paper.title, discussionId)}`
+
+  return [
+    {
+      '@context': 'https://schema.org',
+      '@type': 'ScholarlyArticle',
+      headline: paper.title,
+      name: paper.title,
+      identifier: paper.doi ? `https://doi.org/${paper.doi}` : undefined,
+      author: authors.length > 0 ? authors : undefined,
+      datePublished: paper.year ? `${paper.year}` : undefined,
+      publisher: paper.journal
+        ? { '@type': 'Organization', name: paper.journal }
+        : undefined,
+      description: paper.abstract || undefined,
+      url: pageUrl,
+      isPartOf: {
+        '@type': 'WebSite',
+        name: SITE_NAME,
+        url: SITE_URL,
+      },
+    },
+    {
+      '@context': 'https://schema.org',
+      '@type': 'DiscussionForumPosting',
+      headline: paper.title,
+      name: paper.title,
+      url: pageUrl,
+      datePublished: discussionCreatedAt,
+      author: startedBy
+        ? { '@type': 'Person', name: startedBy }
+        : { '@type': 'Organization', name: SITE_NAME },
+      about: {
+        '@type': 'ScholarlyArticle',
+        headline: paper.title,
+        identifier: paper.doi ? `https://doi.org/${paper.doi}` : undefined,
+      },
+      isPartOf: {
+        '@type': 'WebSite',
+        name: SITE_NAME,
+        url: SITE_URL,
+      },
+    },
+  ]
+}
+
+export async function generateMetadata({ params }) {
+  const { slug } = await params
+  const id = parseDiscussionId(slug)
+  if (!id) {
+    return {
+      title: 'Discussion — PostScholar',
+      description: 'Academic discussion on PostScholar',
+    }
+  }
+
+  const data = await getDiscussionData(id)
+  if (!data || data.error) {
+    return {
+      title: 'Discussion — PostScholar',
+      description: 'Academic discussion on PostScholar',
+    }
+  }
+
+  const { paper } = data
+  const authors =
+    paper.authors_json?.map(a => `${a.given} ${a.family}`).join(', ') || ''
+  const title = paper.title ? `${paper.title} — PostScholar` : 'Discussion — PostScholar'
+  const description = paper.abstract
+    ? paper.abstract.slice(0, 160)
+    : `Discussion of "${paper.title}" on PostScholar`
+  const canonicalSlug = buildDiscussionSlug(paper.title, id)
+  const canonicalPath = `/d/${canonicalSlug}`
+
+  return {
+    title,
+    description,
+    alternates: {
+      canonical: canonicalPath,
+    },
+    openGraph: {
+      title: paper.title,
+      description: paper.abstract?.slice(0, 200) || description,
+      type: 'article',
+      url: canonicalPath,
+      siteName: SITE_NAME,
+      locale: 'en_US',
+      authors: authors ? [authors] : undefined,
+      publishedTime: data.discussion_created_at,
+    },
+    twitter: {
+      card: 'summary_large_image',
+      title: paper.title,
+      description: paper.abstract?.slice(0, 200) || description,
+    },
+  }
+}
+
+export default async function DiscussionPage({ params }) {
+  const { slug } = await params
+  const id = parseDiscussionId(slug)
+
+  if (!id) {
+    return (
+      <Layout>
+        <p className={styles.error}>Discussion not found.</p>
+      </Layout>
+    )
+  }
+
+  const data = await getDiscussionData(id)
+
+  if (!data || data.error) {
+    return (
+      <Layout>
+        <p className={styles.error}>Discussion not found.</p>
+      </Layout>
+    )
+  }
+
+  const { paper, started_by, discussion_created_at, custom_tags } = data
+  const canonicalSlug = buildDiscussionSlug(paper.title, id)
+
+  if (slug !== canonicalSlug) {
+    redirect(`/d/${canonicalSlug}`)
+  }
+
+  const sidebar = paper ? (
+    <PaperSidebar paper={paper} discussionId={id} />
+  ) : null
+
+  const jsonLd = buildJsonLd({
+    paper,
+    discussionId: id,
+    startedBy: started_by,
+    discussionCreatedAt: discussion_created_at,
+  })
+
+  return (
+    <Layout sidebar={sidebar}>
+      <script
+        type="application/ld+json"
+        dangerouslySetInnerHTML={{ __html: JSON.stringify(jsonLd) }}
+      />
+      <Link href="/explore" className="backLink">
+        ← Discussions
+      </Link>
+      {paper && (
+        <PaperHeader
+          paper={paper}
+          startedBy={started_by}
+          discussionCreatedAt={discussion_created_at}
+          customTags={custom_tags || []}
+          discussionId={id}
+        />
+      )}
+      <div className={styles.divider} />
+      <DiscussionComments discussionId={id} />
+    </Layout>
+  )
+}
diff --git a/client-next/src/app/explore/Explore.module.css b/client-next/src/app/explore/Explore.module.css
index ec8ce9c..6984f3f 100644
--- a/client-next/src/app/explore/Explore.module.css
+++ b/client-next/src/app/explore/Explore.module.css
@@ -186,6 +186,71 @@
   cursor: not-allowed;
 }
 
+.activeSection {
+  margin-bottom: var(--space-8);
+  padding: var(--space-5);
+  background: var(--bg-surface);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-md);
+}
+
+.activeHeader {
+  margin-bottom: var(--space-4);
+}
+
+.activeHeading {
+  font-size: var(--text-lg);
+  font-weight: 600;
+  color: var(--text-primary);
+  margin: 0 0 var(--space-1);
+}
+
+.activeSubheading {
+  font-size: var(--text-sm);
+  color: var(--text-muted);
+  margin: 0;
+}
+
+.activeGrid {
+  display: grid;
+  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
+  gap: var(--space-3);
+}
+
+.activeCard {
+  display: block;
+  padding: var(--space-4);
+  background: var(--bg-base);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  text-decoration: none;
+  transition: border-color 0.15s, box-shadow 0.15s;
+}
+
+.activeCard:hover {
+  border-color: var(--accent);
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.04);
+}
+
+.activeTitle {
+  font-size: var(--text-sm);
+  font-weight: 600;
+  color: var(--text-primary);
+  margin: 0 0 var(--space-2);
+  line-height: var(--leading-normal);
+  display: -webkit-box;
+  -webkit-line-clamp: 2;
+  -webkit-box-orient: vertical;
+  overflow: hidden;
+}
+
+.activeMeta {
+  font-size: var(--text-xs);
+  color: var(--text-muted);
+  margin: 0;
+  font-family: var(--font-mono);
+}
+
 @media (max-width: 600px) {
   .heading {
     font-size: var(--text-xl);
@@ -197,4 +262,12 @@
     min-height: 44px;
     padding: var(--space-2) var(--space-4);
   }
+
+  .activeGrid {
+    grid-template-columns: 1fr;
+  }
+
+  .activeSection {
+    padding: var(--space-4);
+  }
 }
diff --git a/client-next/src/app/explore/ExploreFeed.jsx b/client-next/src/app/explore/ExploreFeed.jsx
index 7b22890..7748b8a 100644
--- a/client-next/src/app/explore/ExploreFeed.jsx
+++ b/client-next/src/app/explore/ExploreFeed.jsx
@@ -3,7 +3,9 @@
 import { useState, useEffect, useRef } from 'react'
 import { useSearchParams } from 'next/navigation'
 import { useAuth } from '@/context/AuthContext'
+import Link from 'next/link'
 import { getFollowingFeed, getBookmarks, getExplore, normalizeDiscussion } from '@/lib/api'
+import { discussionPath } from '@/lib/discussionSlug'
 import FeedCard from '@/components/FeedCard'
 import BrowseSidebar from '@/components/BrowseSidebar'
 import SuggestedAuthors from '@/components/SuggestedAuthors'
@@ -28,7 +30,24 @@ const SORT_OPTIONS = [
   { value: 'pub_date_asc',  label: 'Publication date ↑' },
 ]
 
-export default function ExploreFeed({ initialDiscussions, initialTopics, initialNextCursor = null }) {
+function formatActivityTime(isoString) {
+  if (!isoString) return ''
+  const diff = Date.now() - new Date(isoString).getTime()
+  const mins = Math.floor(diff / 60000)
+  const hours = Math.floor(diff / 3600000)
+  const days = Math.floor(diff / 86400000)
+  if (mins < 1) return 'just now'
+  if (mins < 60) return `${mins}m ago`
+  if (hours < 24) return `${hours}h ago`
+  return `${days}d ago`
+}
+
+export default function ExploreFeed({
+  initialDiscussions,
+  initialTopics,
+  initialNextCursor = null,
+  initialRecentlyActive = [],
+}) {
   const { user } = useAuth()
   const searchParams = useSearchParams()
   const topicFromUrl = searchParams.get('topic') || ''
@@ -41,6 +60,9 @@ export default function ExploreFeed({ initialDiscussions, initialTopics, initial
   const [loadingMore, setLoadingMore] = useState(false)
   const [error, setError] = useState('')
   const [nextCursor, setNextCursor] = useState(initialNextCursor)
+  const [recentlyActive] = useState(
+    (initialRecentlyActive || []).map(normalizeDiscussion)
+  )
 
   const [activeFilter, setActiveFilter] = useState('All')
   const [activeTopic, setActiveTopic] = useState(topicFromUrl)
@@ -163,6 +185,34 @@ export default function ExploreFeed({ initialDiscussions, initialTopics, initial
           <p className={styles.subheading}>Browse and filter academic paper threads</p>
         </div>
 
+        {recentlyActive.length > 0 && activeFilter === 'All' && !activeTopic && (
+          <section className={styles.activeSection} aria-label="Recently active discussions">
+            <div className={styles.activeHeader}>
+              <h2 className={styles.activeHeading}>Recently active</h2>
+              <p className={styles.activeSubheading}>
+                Discussions with recent comments
+              </p>
+            </div>
+            <div className={styles.activeGrid}>
+              {recentlyActive.map(d => (
+                <Link
+                  key={d.id}
+                  href={discussionPath({ id: d.id, title: d.title })}
+                  className={styles.activeCard}
+                >
+                  <h3 className={styles.activeTitle}>{d.title}</h3>
+                  <p className={styles.activeMeta}>
+                    {d.comment_count} comment{d.comment_count === 1 ? '' : 's'}
+                    {d.latest_activity && (
+                      <> · {formatActivityTime(d.latest_activity)}</>
+                    )}
+                  </p>
+                </Link>
+              ))}
+            </div>
+          </section>
+        )}
+
         <div className={styles.controlsRow}>
           <div className={styles.mobileBrowse}>
             <p className={styles.mobileBrowseLabel}>Browse</p>
diff --git a/client-next/src/app/explore/page.js b/client-next/src/app/explore/page.js
index 0ae37db..3e4aede 100644
--- a/client-next/src/app/explore/page.js
+++ b/client-next/src/app/explore/page.js
@@ -4,13 +4,24 @@ import { getInitialFeedData } from '@/lib/feedData'
 import { Suspense } from 'react'
 
 export const metadata = {
-  title: 'Explore discussions — PostScholar',
+  title: 'Explore discussions',
+  description:
+    'Browse active academic paper discussions on PostScholar. Filter by topic, sort by recent activity, and join the conversation.',
+  alternates: {
+    canonical: '/explore',
+  },
+  openGraph: {
+    title: 'Explore discussions — PostScholar',
+    description: 'Browse and join academic paper discussions.',
+    url: '/explore',
+  },
 }
 
 export const dynamic = 'force-dynamic'
 
 export default async function ExplorePage() {
-  const { discussions, topics, nextCursor } = await getInitialFeedData()
+  const { discussions, topics, nextCursor, recentlyActive } =
+    await getInitialFeedData()
 
   return (
     <Layout wide>
@@ -19,6 +30,7 @@ export default async function ExplorePage() {
           initialDiscussions={discussions}
           initialTopics={topics}
           initialNextCursor={nextCursor}
+          initialRecentlyActive={recentlyActive}
         />
       </Suspense>
     </Layout>
diff --git a/client-next/src/app/layout.js b/client-next/src/app/layout.js
index 486ea89..43e7c93 100644
--- a/client-next/src/app/layout.js
+++ b/client-next/src/app/layout.js
@@ -1,16 +1,33 @@
 import './globals.css'
 import Providers from './Providers'
 import ErrorBoundary from '@/components/ErrorBoundary'
+import { SITE_NAME, SITE_URL } from '@/lib/site'
 
 export const metadata = {
-  title: 'PostScholar — Academic discussion for published research',
-  description: 'Start or join a discussion on any published paper. Paste a DOI. Verified authors get a badge via ORCID.',
+  metadataBase: new URL(SITE_URL),
+  title: {
+    default: `${SITE_NAME} — Academic discussion for published research`,
+    template: `%s — ${SITE_NAME}`,
+  },
+  description:
+    'Start or join a discussion on any published paper. Paste a DOI. Verified authors get a badge via ORCID.',
   openGraph: {
-    title: 'PostScholar',
+    title: SITE_NAME,
     description: 'Academic discussion for published research',
-    url: 'https://postscholar.org',
+    url: SITE_URL,
+    siteName: SITE_NAME,
+    locale: 'en_US',
     type: 'website',
   },
+  twitter: {
+    card: 'summary_large_image',
+    title: SITE_NAME,
+    description: 'Academic discussion for published research',
+  },
+  robots: {
+    index: true,
+    follow: true,
+  },
 }
 
 export const viewport = {
diff --git a/client-next/src/app/privacy/page.js b/client-next/src/app/privacy/page.js
index 3474d74..8280904 100644
--- a/client-next/src/app/privacy/page.js
+++ b/client-next/src/app/privacy/page.js
@@ -3,7 +3,11 @@ import Layout from '@/components/Layout'
 import styles from './Privacy.module.css'
 
 export const metadata = {
-  title: 'Privacy Policy — PostScholar',
+  title: 'Privacy Policy',
+  description: 'Privacy Policy for PostScholar — how we collect and use your data.',
+  alternates: {
+    canonical: '/privacy',
+  },
 }
 
 export default function PrivacyPage() {
@@ -59,6 +63,8 @@ export default function PrivacyPage() {
         </section>
 
         <p className={styles.back}>
+          <Link href="/terms" className={styles.link}>Terms of Service</Link>
+          {' · '}
           <Link href="/" className={styles.link}>← Back to home</Link>
         </p>
       </div>
diff --git a/client-next/src/app/robots.js b/client-next/src/app/robots.js
new file mode 100644
index 0000000..8d6129a
--- /dev/null
+++ b/client-next/src/app/robots.js
@@ -0,0 +1,12 @@
+import { SITE_URL } from '@/lib/site'
+
+export default function robots() {
+  return {
+    rules: {
+      userAgent: '*',
+      allow: '/',
+      disallow: ['/settings', '/moderation', '/login', '/register'],
+    },
+    sitemap: `${SITE_URL}/sitemap.xml`,
+  }
+}
diff --git a/client-next/src/app/sitemap.js b/client-next/src/app/sitemap.js
new file mode 100644
index 0000000..a877003
--- /dev/null
+++ b/client-next/src/app/sitemap.js
@@ -0,0 +1,44 @@
+import { getServerApiUrl } from '@/lib/config'
+import { buildDiscussionSlug } from '@/lib/discussionSlug'
+import { SITE_URL } from '@/lib/site'
+
+export default async function sitemap() {
+  const staticPages = [
+    { path: '', changeFrequency: 'daily', priority: 1 },
+    { path: '/explore', changeFrequency: 'hourly', priority: 0.9 },
+    { path: '/search', changeFrequency: 'weekly', priority: 0.7 },
+    { path: '/start', changeFrequency: 'monthly', priority: 0.8 },
+    { path: '/about', changeFrequency: 'monthly', priority: 0.6 },
+    { path: '/privacy', changeFrequency: 'yearly', priority: 0.3 },
+    { path: '/terms', changeFrequency: 'yearly', priority: 0.3 },
+  ]
+
+  const entries = staticPages.map(({ path, changeFrequency, priority }) => ({
+    url: `${SITE_URL}${path}`,
+    lastModified: new Date(),
+    changeFrequency,
+    priority,
+  }))
+
+  try {
+    const res = await fetch(`${getServerApiUrl()}/sitemap/discussions`, {
+      next: { revalidate: 3600 },
+    })
+
+    if (res.ok) {
+      const data = await res.json()
+      for (const row of data.discussions || []) {
+        entries.push({
+          url: `${SITE_URL}/d/${buildDiscussionSlug(row.title, row.id)}`,
+          lastModified: new Date(row.last_modified || row.created_at),
+          changeFrequency: 'weekly',
+          priority: 0.8,
+        })
+      }
+    }
+  } catch (error) {
+    console.error('sitemap: failed to fetch discussions', error)
+  }
+
+  return entries
+}
diff --git a/client-next/src/app/start/page.js b/client-next/src/app/start/page.js
index 5594042..7cb2d63 100644
--- a/client-next/src/app/start/page.js
+++ b/client-next/src/app/start/page.js
@@ -6,6 +6,7 @@ import { useRouter } from 'next/navigation'
 import { useAuth } from '@/context/AuthContext'
 import Layout from '@/components/Layout'
 import { postComment } from '@/lib/api'
+import { discussionPath } from '@/lib/discussionSlug'
 import { getApiUrl } from '@/lib/config'
 import styles from './Start.module.css'
 
@@ -146,7 +147,12 @@ export default function Start() {
 
       // If a discussion already exists for this paper, redirect immediately
       if (data.existed && data.discussion_id) {
-        router.push(`/d/${data.discussion_id}`)
+        router.push(
+          discussionPath({
+            id: data.discussion_id,
+            title: data.paper?.title,
+          })
+        )
         return
       }
 
@@ -185,7 +191,7 @@ export default function Start() {
         await postComment(discussion_id, openingComment.trim())
       }
 
-      router.push(`/d/${discussion_id}`)
+      router.push(discussionPath({ id: discussion_id, title: paper.title }))
     } catch (err) {
       setErrorMsg(err.message)
     } finally {
@@ -232,7 +238,12 @@ export default function Start() {
         await postComment(discussionData.discussion_id, openingComment.trim())
       }
 
-      router.push(`/d/${discussionData.discussion_id}`)
+      router.push(
+        discussionPath({
+          id: discussionData.discussion_id,
+          title: manual.title || paperData.paper?.title,
+        })
+      )
     } catch (err) {
       setErrorMsg(err.message)
     } finally {
diff --git a/client-next/src/app/terms/page.js b/client-next/src/app/terms/page.js
new file mode 100644
index 0000000..7b20454
--- /dev/null
+++ b/client-next/src/app/terms/page.js
@@ -0,0 +1,108 @@
+import Link from 'next/link'
+import Layout from '@/components/Layout'
+import styles from '../privacy/Privacy.module.css'
+
+export const metadata = {
+  title: 'Terms of Service — PostScholar',
+  description:
+    'Terms of Service for PostScholar — academic discussion platform for published research.',
+  alternates: {
+    canonical: '/terms',
+  },
+}
+
+export default function TermsPage() {
+  return (
+    <Layout>
+      <div className={styles.page}>
+        <h1 className={styles.heading}>Terms of Service</h1>
+        <p className={styles.updated}>Last updated: June 2026</p>
+
+        <section className={styles.section}>
+          <h2>Acceptance</h2>
+          <p>
+            By using PostScholar, you agree to these terms. If you do not agree,
+            please do not use the service.
+          </p>
+        </section>
+
+        <section className={styles.section}>
+          <h2>What PostScholar is</h2>
+          <p>
+            PostScholar is a platform for scholarly discussion of published
+            research. Users may start or join discussions about papers identified
+            by DOI or metadata. We are not a publisher and do not host full-text
+            papers unless linked externally by users.
+          </p>
+        </section>
+
+        <section className={styles.section}>
+          <h2>Your account and content</h2>
+          <p>
+            You are responsible for your account and for content you post. You
+            must not post spam, harassment, illegal material, or content that
+            infringes others&apos; rights. You retain ownership of your posts;
+            you grant PostScholar a non-exclusive license to display and
+            distribute them on the platform.
+          </p>
+        </section>
+
+        <section className={styles.section}>
+          <h2>Academic conduct</h2>
+          <p>
+            Discussions should stay relevant to the paper at hand. Critique ideas,
+            not people. Misrepresentation of authorship or credentials is not
+            permitted. ORCID verification badges reflect successful verification
+            for a specific discussion only.
+          </p>
+        </section>
+
+        <section className={styles.section}>
+          <h2>Moderation</h2>
+          <p>
+            We may remove content or suspend accounts that violate these terms or
+            our community standards. Users may report comments; moderators review
+            reports and take appropriate action.
+          </p>
+        </section>
+
+        <section className={styles.section}>
+          <h2>Disclaimer</h2>
+          <p>
+            PostScholar is provided &quot;as is.&quot; Discussion content reflects
+            user opinions, not PostScholar&apos;s views. We do not guarantee
+            accuracy of user comments or third-party paper metadata.
+          </p>
+        </section>
+
+        <section className={styles.section}>
+          <h2>Changes</h2>
+          <p>
+            We may update these terms. Continued use after changes constitutes
+            acceptance. Material changes will be noted on this page.
+          </p>
+        </section>
+
+        <section className={styles.section}>
+          <h2>Contact</h2>
+          <p>
+            Questions? Contact{' '}
+            <a href="mailto:hello@postscholar.org" className={styles.link}>
+              hello@postscholar.org
+            </a>.
+          </p>
+        </section>
+
+        <p className={styles.back}>
+          <Link href="/privacy" className={styles.link}>
+            Privacy Policy
+          </Link>
+          {' · '}
+          <Link href="/" className={styles.link}>
+            ← Back to home
+          </Link>
+        </p>
+      </div>
+    </Layout>
+  )
+}
diff --git a/client-next/src/app/u/[username]/ProfileClient.jsx b/client-next/src/app/u/[username]/ProfileClient.jsx
index afe9944..dc3fa33 100644
--- a/client-next/src/app/u/[username]/ProfileClient.jsx
+++ b/client-next/src/app/u/[username]/ProfileClient.jsx
@@ -2,6 +2,7 @@
 
 import { useState, useEffect } from 'react'
 import Link from 'next/link'
+import { discussionPath } from '@/lib/discussionSlug'
 import { useAuth } from '@/context/AuthContext'
 import { followUser, unfollowUser, getFollowStatus, getFollowCounts } from '@/lib/api'
 import styles from './Profile.module.css'
@@ -185,7 +186,11 @@ export default function ProfileClient({ profile }) {
                 </p>
               ) : (
                 discussions.map(d => (
-                  <Link key={d.id} href={`/d/${d.id}`} className={styles.activityCard}>
+                  <Link
+                    key={d.id}
+                    href={discussionPath({ id: d.id, title: d.title })}
+                    className={styles.activityCard}
+                  >
                     <h3 className={`${styles.cardTitle} paper-title`}>{d.title}</h3>
                     <p className={styles.cardMeta}>
                       {[d.journal, d.year].filter(Boolean).join(' · ')}
@@ -210,7 +215,14 @@ export default function ProfileClient({ profile }) {
                 </p>
               ) : (
                 comments.map(c => (
-                  <Link key={c.id} href={`/d/${c.discussion_id}`} className={styles.activityCard}>
+                  <Link
+                    key={c.id}
+                    href={discussionPath({
+                      id: c.discussion_id,
+                      title: c.paper_title,
+                    })}
+                    className={styles.activityCard}
+                  >
                     <p className={styles.cardLabel}>Comment on</p>
                     <h3 className={`${styles.cardTitle} paper-title`}>{c.paper_title}</h3>
                     <p className={styles.cardBody}>
diff --git a/client-next/src/components/Comment.jsx b/client-next/src/components/Comment.jsx
index ee67ece..cfabb8c 100644
--- a/client-next/src/components/Comment.jsx
+++ b/client-next/src/components/Comment.jsx
@@ -1,12 +1,18 @@
 'use client'
 
-import { useState } from 'react'
+import { useState, useEffect } from 'react'
 import Link from 'next/link'
 import { useRouter } from 'next/navigation'
-import { Flag } from 'lucide-react'
+import { Flag, Plus } from 'lucide-react'
 import { useAuth } from '@/context/AuthContext'
 import AuthorBadge from './AuthorBadge'
-import { postComment, editComment, deleteComment, submitReport } from '@/lib/api'
+import {
+  postComment,
+  editComment,
+  deleteComment,
+  submitReport,
+  toggleCommentReaction,
+} from '@/lib/api'
 import CommentBody from './CommentBody'
 import styles from './Comment.module.css'
 import 'katex/dist/katex.min.css'
@@ -56,8 +62,30 @@ export default function Comment({
   const [reportLoading, setReportLoading] = useState(false)
   const [reportSuccess, setReportSuccess] = useState(false)
 
+  const [reactionCount, setReactionCount] = useState(comment.reaction_count || 0)
+  const [userReacted, setUserReacted] = useState(comment.user_reacted || false)
+  const [reactionLoading, setReactionLoading] = useState(false)
+
+  const [repliesCollapsed, setRepliesCollapsed] = useState(depth >= 2)
+  const [isMobile, setIsMobile] = useState(false)
+
   const isOwn = user && user.username === comment.username
   const indentLevel = Math.min(depth, 4)
+  const replyCount = comment.replies?.length || 0
+  const collapseReplies = isMobile && depth >= 2 && replyCount > 0
+
+  useEffect(() => {
+    const mq = window.matchMedia('(max-width: 600px)')
+    const update = () => setIsMobile(mq.matches)
+    update()
+    mq.addEventListener('change', update)
+    return () => mq.removeEventListener('change', update)
+  }, [])
+
+  useEffect(() => {
+    setReactionCount(comment.reaction_count || 0)
+    setUserReacted(comment.user_reacted || false)
+  }, [comment.reaction_count, comment.user_reacted])
 
   function handleReplyClick() {
     if (!user) {
@@ -115,6 +143,25 @@ export default function Comment({
     }
   }
 
+  async function handleReaction() {
+    if (!user) {
+      router.push('/login')
+      return
+    }
+    if (reactionLoading) return
+
+    setReactionLoading(true)
+    try {
+      const data = await toggleCommentReaction(comment.id)
+      setReactionCount(data.reaction_count)
+      setUserReacted(data.reacted)
+    } catch (err) {
+      alert(err.message)
+    } finally {
+      setReactionLoading(false)
+    }
+  }
+
   async function handleReportSubmit(e) {
     e.preventDefault()
     if (!reportReason) return
@@ -197,6 +244,19 @@ export default function Comment({
         {/* Actions */}
         {!editing && (
           <div className={styles.actions}>
+            <button
+              type="button"
+              className={`${styles.reactionBtn} ${userReacted ? styles.reactionActive : ''}`}
+              onClick={handleReaction}
+              disabled={reactionLoading}
+              aria-label={userReacted ? 'Remove appreciation' : 'Appreciate comment'}
+              title={user ? 'Appreciate this comment' : 'Sign in to appreciate'}
+            >
+              <Plus size={14} strokeWidth={2.5} />
+              {reactionCount > 0 && (
+                <span className={styles.reactionCount}>{reactionCount}</span>
+              )}
+            </button>
             <button className={styles.actionBtn} onClick={handleReplyClick}>
               Reply
             </button>
@@ -311,17 +371,36 @@ export default function Comment({
         {/* Nested replies */}
         {comment.replies?.length > 0 && (
           <div className={styles.replies}>
-            {comment.replies.map(reply => (
-              <Comment
-                key={reply.id}
-                comment={reply}
-                discussionId={discussionId}
-                onReplyPosted={onReplyPosted}
-                onEdited={onEdited}
-                onDeleted={onDeleted}
-                depth={depth + 1}
-              />
-            ))}
+            {collapseReplies && repliesCollapsed && (
+              <button
+                type="button"
+                className={styles.collapseToggle}
+                onClick={() => setRepliesCollapsed(false)}
+              >
+                Show {replyCount} repl{replyCount === 1 ? 'y' : 'ies'}
+              </button>
+            )}
+            {(!collapseReplies || !repliesCollapsed) &&
+              comment.replies.map(reply => (
+                <Comment
+                  key={reply.id}
+                  comment={reply}
+                  discussionId={discussionId}
+                  onReplyPosted={onReplyPosted}
+                  onEdited={onEdited}
+                  onDeleted={onDeleted}
+                  depth={depth + 1}
+                />
+              ))}
+            {collapseReplies && !repliesCollapsed && (
+              <button
+                type="button"
+                className={styles.collapseToggle}
+                onClick={() => setRepliesCollapsed(true)}
+              >
+                Hide replies
+              </button>
+            )}
           </div>
         )}
       </div>
diff --git a/client-next/src/components/Comment.module.css b/client-next/src/components/Comment.module.css
index 90b1805..be1823e 100644
--- a/client-next/src/components/Comment.module.css
+++ b/client-next/src/components/Comment.module.css
@@ -23,12 +23,14 @@
 
 @media (max-width: 600px) {
   .comment {
-    --comment-indent: 10px;
+    --comment-indent: 14px;
     gap: var(--space-2);
   }
 
   .threadLine {
-    display: none;
+    display: block;
+    opacity: 0.5;
+    left: calc(var(--indent, 0) * var(--comment-indent, 14px) - 8px);
   }
 
   .comment[data-is-author="true"] .body {
@@ -119,6 +121,55 @@
   display: flex;
   gap: var(--space-3);
   margin-top: var(--space-3);
+  align-items: center;
+}
+
+.reactionBtn {
+  display: inline-flex;
+  align-items: center;
+  gap: 4px;
+  font-size: var(--text-xs);
+  font-weight: 500;
+  color: var(--text-muted);
+  background: none;
+  border: 1px solid var(--border);
+  border-radius: var(--radius-sm);
+  padding: 2px 8px;
+  cursor: pointer;
+  transition: color 0.15s, border-color 0.15s, background 0.15s;
+}
+
+.reactionBtn:hover:not(:disabled) {
+  color: var(--accent);
+  border-color: var(--accent);
+}
+
+.reactionActive {
+  color: var(--accent);
+  border-color: var(--accent);
+  background: color-mix(in srgb, var(--accent) 8%, transparent);
+}
+
+.reactionCount {
+  font-family: var(--font-mono);
+  font-size: var(--text-xs);
+}
+
+.collapseToggle {
+  display: block;
+  width: 100%;
+  text-align: left;
+  font-size: var(--text-xs);
+  font-weight: 500;
+  color: var(--accent);
+  background: none;
+  border: none;
+  padding: var(--space-2) 0;
+  cursor: pointer;
+}
+
+.collapseToggle:hover {
+  text-decoration: underline;
 }
 
 .actionBtn {
diff --git a/client-next/src/components/CommentThread.jsx b/client-next/src/components/CommentThread.jsx
index 1bf593a..ccaaa7c 100644
--- a/client-next/src/components/CommentThread.jsx
+++ b/client-next/src/components/CommentThread.jsx
@@ -12,7 +12,7 @@ import styles from './CommentThread.module.css'
  * CommentThread
  *
  * Renders the full comment section for a discussion.
- * Supports sort options: oldest, newest, top (most replied).
+ * Supports sort options: oldest, newest, top (most appreciated).
  *
  * Props:
  *   discussionId  — UUID
@@ -26,7 +26,7 @@ import styles from './CommentThread.module.css'
 const COMMENT_SORT_OPTIONS = [
   { value: 'oldest', label: 'Oldest first' },
   { value: 'newest', label: 'Newest first' },
-  { value: 'top',    label: 'Most replied' },
+  { value: 'top',    label: 'Most appreciated' },
 ]
 
 export default function CommentThread({
diff --git a/client-next/src/components/FeedCard.jsx b/client-next/src/components/FeedCard.jsx
index aa545c7..41ae63c 100644
--- a/client-next/src/components/FeedCard.jsx
+++ b/client-next/src/components/FeedCard.jsx
@@ -7,6 +7,7 @@ import { Bookmark } from 'lucide-react'
 import ShareButton from './ShareButton'
 import styles from './FeedCard.module.css'
 import { createBookmark, removeBookmark, checkBookmark, normalizeDiscussion } from '@/lib/api'
+import { discussionPath } from '@/lib/discussionSlug'
 import { useAuth } from '@/context/AuthContext'
 
 /**
@@ -57,6 +58,7 @@ export default function FeedCard({ discussion: rawDiscussion }) {
 
   const unanswered = comment_count === 0
   const authorLine = formatAuthors(authors_json)
+  const href = discussionPath({ id, title })
 
   useEffect(() => {
     if (user) {
@@ -94,7 +96,7 @@ export default function FeedCard({ discussion: rawDiscussion }) {
   return (
     <article className={styles.card}>
       <div className={styles.cardBody}>
-        <Link href={`/d/${id}`} className={styles.titleLink}>
+        <Link href={href} className={styles.titleLink}>
           <h2 className={`${styles.title} paper-title`}>{title}</h2>
         </Link>
 
@@ -142,7 +144,7 @@ export default function FeedCard({ discussion: rawDiscussion }) {
 
       <div className={styles.cardActions}>
         <ShareButton
-          url={typeof window !== 'undefined' ? `${window.location.origin}/d/${id}` : `/d/${id}`}
+          url={typeof window !== 'undefined' ? `${window.location.origin}${href}` : href}
           title={title}
           size={18}
         />
diff --git a/client-next/src/components/Footer.jsx b/client-next/src/components/Footer.jsx
index b12cd27..38360db 100644
--- a/client-next/src/components/Footer.jsx
+++ b/client-next/src/components/Footer.jsx
@@ -9,6 +9,7 @@ export default function Footer() {
         <Link href="/explore" className={styles.link}>Discussions</Link>
         <Link href="/about" className={styles.link}>About</Link>
         <Link href="/privacy" className={styles.link}>Privacy</Link>
+        <Link href="/terms" className={styles.link}>Terms</Link>
         <Link href="/start" className={styles.link}>Start a discussion</Link>
       </div>
       <p className={styles.text}>
diff --git a/client-next/src/lib/api.js b/client-next/src/lib/api.js
index dfbcaa3..c280355 100644
--- a/client-next/src/lib/api.js
+++ b/client-next/src/lib/api.js
@@ -101,6 +101,10 @@ export function deleteComment(commentId) {
   return api.delete(`/discussions/comments/${commentId}`)
 }
 
+export function toggleCommentReaction(commentId) {
+  return api.post(`/discussions/comments/${commentId}/react`, {})
+}
+
 /**
  * Delete an entire discussion. Creator only.
  * Returns { deleted: true }
@@ -286,6 +290,10 @@ export function checkTopicFollow(topic) {
   return api.get(`/topic-follows/check?topic=${encodeURIComponent(topic)}`)
 }
 
+export function getRecentlyActive(limit = 6) {
+  return api.get(`/explore/active?limit=${limit}`)
+}
+
 export function getExplore({ filter, topic, sort, cursor } = {}) {
   const params = new URLSearchParams()
   if (filter) params.set('filter', filter)
diff --git a/client-next/src/lib/discussionSlug.js b/client-next/src/lib/discussionSlug.js
new file mode 100644
index 0000000..4d68c0d
--- /dev/null
+++ b/client-next/src/lib/discussionSlug.js
@@ -0,0 +1,34 @@
+const UUID_RE =
+  /[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i
+
+const UUID_ONLY_RE =
+  /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i
+
+export function slugifyTitle(title) {
+  if (!title) return 'discussion'
+  return title
+    .toLowerCase()
+    .normalize('NFKD')
+    .replace(/[\u0300-\u036f]/g, '')
+    .replace(/[^a-z0-9]+/g, '-')
+    .replace(/^-+|-+$/g, '')
+    .slice(0, 80)
+    || 'discussion'
+}
+
+export function buildDiscussionSlug(title, id) {
+  return `${slugifyTitle(title)}-${id}`
+}
+
+export function parseDiscussionId(slug) {
+  if (!slug) return null
+  if (UUID_ONLY_RE.test(slug)) return slug
+  const match = slug.match(UUID_RE)
+  return match ? match[0] : null
+}
+
+export function discussionPath({ id, title }) {
+  if (!id) return '/explore'
+  const slug = title ? buildDiscussionSlug(title, id) : id
+  return `/d/${slug}`
+}
diff --git a/client-next/src/lib/feedData.js b/client-next/src/lib/feedData.js
index fba6009..a195fa1 100644
--- a/client-next/src/lib/feedData.js
+++ b/client-next/src/lib/feedData.js
@@ -4,20 +4,23 @@ export async function getInitialFeedData() {
   const baseUrl = getServerApiUrl()
 
   try {
-    const [discussionsRes, topicsRes] = await Promise.all([
+    const [discussionsRes, topicsRes, activeRes] = await Promise.all([
       fetch(`${baseUrl}/explore`, { cache: 'no-store' }),
       fetch(`${baseUrl}/topics`, { cache: 'no-store' }),
+      fetch(`${baseUrl}/explore/active?limit=6`, { cache: 'no-store' }),
     ])
 
-    const [discussionsData, topicsData] = await Promise.all([
+    const [discussionsData, topicsData, activeData] = await Promise.all([
       discussionsRes.ok ? discussionsRes.json() : { discussions: [] },
       topicsRes.ok ? topicsRes.json() : { topics: [] },
+      activeRes.ok ? activeRes.json() : { discussions: [] },
     ])
 
     return {
       discussions: discussionsData.discussions || [],
       topics: topicsData.topics || [],
       nextCursor: discussionsData.next_cursor || null,
+      recentlyActive: activeData.discussions || [],
     }
   } catch (error) {
     console.error('Failed to fetch initial feed data:', error)
@@ -25,6 +28,7 @@ export async function getInitialFeedData() {
       discussions: [],
       topics: [],
       nextCursor: null,
+      recentlyActive: [],
     }
   }
 }
diff --git a/client-next/src/lib/site.js b/client-next/src/lib/site.js
new file mode 100644
index 0000000..4f86064
--- /dev/null
+++ b/client-next/src/lib/site.js
@@ -0,0 +1,4 @@
+export const SITE_URL =
+  process.env.NEXT_PUBLIC_SITE_URL || 'https://postscholar.org'
+
+export const SITE_NAME = 'PostScholar'
diff --git a/docs/DEVELOPER_NOTES.md b/docs/DEVELOPER_NOTES.md
index d85d6da..8921427 100644
--- a/docs/DEVELOPER_NOTES.md
+++ b/docs/DEVELOPER_NOTES.md
@@ -70,6 +70,10 @@ PostScholar follows a modern client-server architecture:
 - Cascading deletes when parent comment or discussion is deleted
 - Updated timestamps tracked automatically via trigger
 
+**comment_reactions**
+- Upvote-only "+" reactions (one per user per comment)
+- Used for "top" comment sort; no downvotes
+
 **bookmarks**
 - Many-to-many relationship between users and discussions
 - Composite primary key prevents duplicates
@@ -93,7 +97,7 @@ PostScholar follows a modern client-server architecture:
 
 Location: `server/db/migrations/*.sql`
 
-Migrations are numbered sequentially (001-015 currently) and tracked in `schema_migrations` table.
+Migrations are numbered sequentially (001-019 currently) and tracked in `schema_migrations` table.
 
 **Key patterns**:
 ```sql
@@ -277,7 +281,9 @@ src/
 │   ├── layout.js           # Root layout (Nav, Providers, ErrorBoundary)
 │   ├── page.js             # Home page
 │   ├── not-found.js        # 404 page
-│   ├── d/[id]/page.js      # Discussion page
+│   ├── d/[slug]/page.js    # Discussion page (slug-id URLs, JSON-LD)
+│   ├── sitemap.js          # Dynamic sitemap
+│   ├── robots.js           # Crawler rules
 │   ├── explore/page.js     # Explore feed
 │   ├── profile/[username]/ # User profiles
 │   └── settings/page.js    # Settings
@@ -446,22 +452,15 @@ Currently enforced at application layer, not database:
 
 ### Moderation
 
-No role-based access control yet:
-- `GET /reports` is protected but doesn't check if user is moderator
-- TODO: Add `role` column to users table with 'user', 'moderator', 'admin' roles
-- TODO: Add role check middleware
+Role-based access control is implemented (migration `018_user_roles.sql`):
+- `users.role`: `user` | `moderator` | `admin`
+- Moderators access `/moderation` and `GET /reports`
+- Promote via SQL: `UPDATE users SET role = 'moderator' WHERE username = '...';` then re-login
 
 ### Search
 
-Current search is basic SQL ILIKE:
-```sql
-WHERE title ILIKE '%query%' OR abstract ILIKE '%query%'
-```
-
-Future improvements:
-- Full-text search with `tsvector` and `tsquery`
-- Search ranking with `ts_rank`
-- Highlighted snippets
+Discussion search uses PostgreSQL full-text search (`tsvector` / `tsquery`) on papers.
+Comment search within a discussion uses full-text search on comment bodies.
 
 ### Real-time Updates
 
@@ -478,6 +477,45 @@ Limited test coverage:
 - No integration/E2E tests
 - Should add: Jest + React Testing Library + Playwright
 
+## SEO & Discovery
+
+### URL structure
+
+Discussion pages use slug URLs for crawlability:
+
+```
+/d/{slugified-paper-title}-{discussion-uuid}
+```
+
+Legacy `/d/{uuid}` links redirect (308) to the canonical slug URL via `redirect()` in `d/[slug]/page.js`.
+
+Helpers: `client-next/src/lib/discussionSlug.js`, `client-next/src/lib/site.js`.
+
+### Metadata
+
+- Root `layout.js` sets `metadataBase`, Open Graph, and Twitter defaults
+- Discussion pages: `generateMetadata` with canonical URL, article OG tags
+- JSON-LD: `ScholarlyArticle` + `DiscussionForumPosting` on discussion pages
+
+### Sitemap & robots
+
+- **Dynamic sitemap**: `client-next/src/app/sitemap.js` — fetches `GET /sitemap/discussions` from the API, revalidates hourly
+- **robots.txt**: `client-next/src/app/robots.js` — disallows `/settings`, `/moderation`, auth pages
+- Legacy script `client-next/scripts/generate-sitemap.js` is optional fallback only
+
+### Google Search Console (manual)
+
+1. Add property at [Google Search Console](https://search.google.com/search-console) for `https://postscholar.org`
+2. Verify via DNS (Namecheap) or HTML tag
+3. Submit sitemap: `https://postscholar.org/sitemap.xml`
+4. Set preferred domain (apex vs `www`) in GSC; ensure `NEXT_PUBLIC_SITE_URL` matches production canonical
+5. Monitor Coverage and Core Web Vitals after deploy
+
+### Explore discovery
+
+- `GET /explore/active` — recently active discussions (≥1 comment) for the Explore spotlight
+- Default explore sort `recent` uses `latest_activity` (last comment or discussion start)
+
 ## Further Reading
 
 ### Official Documentation
diff --git a/server/db/migrations/019_comment_reactions.sql b/server/db/migrations/019_comment_reactions.sql
new file mode 100644
index 0000000..c256230
--- /dev/null
+++ b/server/db/migrations/019_comment_reactions.sql
@@ -0,0 +1,9 @@
+CREATE TABLE IF NOT EXISTS comment_reactions (
+  comment_id UUID NOT NULL REFERENCES comments(id) ON DELETE CASCADE,
+  user_id    UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+  created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+  PRIMARY KEY (comment_id, user_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_comment_reactions_comment_id
+  ON comment_reactions(comment_id);
diff --git a/server/index.js b/server/index.js
index 6f0ed0c..73b0320 100644
--- a/server/index.js
+++ b/server/index.js
@@ -70,6 +70,7 @@ app.use('/reports', require('./routes/reports'))
 app.use('/follows', require('./routes/follows'))
 app.use('/mentions', require('./routes/mentions'))
 app.use('/topic-follows', require('./routes/topic-follows'))
+app.use('/', require('./routes/sitemap'))
 app.use('/', exploreRouter)
 
 app.use(errorHandler)
diff --git a/server/routes/discussions.js b/server/routes/discussions.js
index 8fc3421..740bef8 100644
--- a/server/routes/discussions.js
+++ b/server/routes/discussions.js
@@ -65,6 +65,54 @@ function sanitizeComment(body) {
   })
 }
 
+function collectCommentIds(tree, ids = []) {
+  for (const comment of tree) {
+    ids.push(comment.id)
+    if (comment.replies?.length) {
+      collectCommentIds(comment.replies, ids)
+    }
+  }
+  return ids
+}
+
+function applyReactions(tree, counts, reacted) {
+  for (const comment of tree) {
+    comment.reaction_count = counts.get(comment.id) || 0
+    comment.user_reacted = reacted.has(comment.id)
+    if (comment.replies?.length) {
+      applyReactions(comment.replies, counts, reacted)
+    }
+  }
+  return tree
+}
+
+async function getReactionData(commentIds, userId) {
+  if (commentIds.length === 0) {
+    return { counts: new Map(), reacted: new Set() }
+  }
+
+  const countsResult = await pool.query(
+    `SELECT comment_id, COUNT(*)::int AS count
+     FROM comment_reactions
+     WHERE comment_id = ANY($1::uuid[])
+     GROUP BY comment_id`,
+    [commentIds]
+  )
+  const counts = new Map(countsResult.rows.map(r => [r.comment_id, r.count]))
+
+  let reacted = new Set()
+  if (userId) {
+    const userResult = await pool.query(
+      `SELECT comment_id FROM comment_reactions
+       WHERE comment_id = ANY($1::uuid[]) AND user_id = $2`,
+      [commentIds, userId]
+    )
+    reacted = new Set(userResult.rows.map(r => r.comment_id))
+  }
+
+  return { counts, reacted }
+}
+
 // ---------------------------------------------------------------------------
 // GET /discussions/:id/comments
 // ---------------------------------------------------------------------------
@@ -101,7 +149,7 @@ router.get('/:id/comments', optionalAuth, async (req, res) => {
         break
       case 'top':
         orderClause = `ORDER BY (
-          SELECT COUNT(*) FROM comments r WHERE r.parent_comment_id = c.id
+          SELECT COUNT(*) FROM comment_reactions r WHERE r.comment_id = c.id
         ) DESC, c.created_at ASC`
         cursorOp = null
         break
@@ -156,6 +204,13 @@ router.get('/:id/comments', optionalAuth, async (req, res) => {
 
       const allComments = [...pageRows, ...descendantsResult.rows]
       tree = buildTree(allComments, verifiedUserIds)
+
+      const commentIds = collectCommentIds(tree)
+      const { counts, reacted } = await getReactionData(
+        commentIds,
+        req.user?.userId || null
+      )
+      applyReactions(tree, counts, reacted)
     }
 
     const nextCursor = hasNextPage ? pageRows[pageRows.length - 1].created_at : null
@@ -396,6 +451,58 @@ router.patch('/comments/:id', authenticateToken, async (req, res) => {
   }
 })
 
+// ---------------------------------------------------------------------------
+// POST /discussions/comments/:id/react
+// ---------------------------------------------------------------------------
+// Protected. Toggle a "+" reaction on a comment (upvote only, no downvote).
+// ---------------------------------------------------------------------------
+router.post('/comments/:id/react', authenticateToken, async (req, res) => {
+  try {
+    const { id } = req.params
+
+    const commentCheck = await pool.query(
+      'SELECT id FROM comments WHERE id = $1',
+      [id]
+    )
+    if (commentCheck.rows.length === 0) {
+      return res.status(404).json({ error: 'Comment not found' })
+    }
+
+    const existing = await pool.query(
+      'SELECT 1 FROM comment_reactions WHERE comment_id = $1 AND user_id = $2',
+      [id, req.user.userId]
+    )
+
+    let reacted
+    if (existing.rows.length > 0) {
+      await pool.query(
+        'DELETE FROM comment_reactions WHERE comment_id = $1 AND user_id = $2',
+        [id, req.user.userId]
+      )
+      reacted = false
+    } else {
+      await pool.query(
+        'INSERT INTO comment_reactions (comment_id, user_id) VALUES ($1, $2)',
+        [id, req.user.userId]
+      )
+      reacted = true
+    }
+
+    const countResult = await pool.query(
+      'SELECT COUNT(*)::int AS count FROM comment_reactions WHERE comment_id = $1',
+      [id]
+    )
+
+    return res.json({
+      reacted,
+      reaction_count: countResult.rows[0].count,
+    })
+  } catch (err) {
+    console.error('POST /discussions/comments/:id/react error:', err)
+    res.status(500).json({ error: 'Internal server error' })
+  }
+})
+
 // ---------------------------------------------------------------------------
 // DELETE /discussions/comments/:id
 // ---------------------------------------------------------------------------
diff --git a/server/routes/explore.js b/server/routes/explore.js
index 4c3fde6..4d9ea10 100644
--- a/server/routes/explore.js
+++ b/server/routes/explore.js
@@ -38,6 +38,62 @@ router.get('/topics', async (req, res) => {
   }
 })
 
+// ---------------------------------------------------------------------------
+// GET /explore/active
+// ---------------------------------------------------------------------------
+// Public. Returns recently active discussions (at least one comment).
+// Used for the Explore "Recently active" spotlight section.
+// ---------------------------------------------------------------------------
+router.get('/explore/active', async (req, res) => {
+  try {
+    const limit = Math.min(parseInt(req.query.limit, 10) || 6, 12)
+
+    const result = await pool.query(
+      `SELECT
+         d.id,
+         d.created_at,
+         p.title,
+         p.authors_json,
+         p.journal,
+         p.year,
+         u.username,
+         (
+           SELECT COUNT(*)
+           FROM comments c
+           WHERE c.discussion_id = d.id
+         )::int AS comment_count,
+         (
+           SELECT MAX(c.created_at)
+           FROM comments c
+           WHERE c.discussion_id = d.id
+         ) AS latest_activity,
+         COALESCE(
+           (
+             SELECT json_agg(json_build_object('name', t.name, 'slug', t.slug))
+             FROM discussion_topics dt
+             JOIN topics t ON t.id = dt.topic_id
+             WHERE dt.discussion_id = d.id
+           ),
+           '[]'::json
+         ) AS topics
+       FROM discussions d
+       JOIN papers p ON p.id = d.paper_id
+       LEFT JOIN users u ON u.id = d.created_by
+       WHERE EXISTS (
+         SELECT 1 FROM comments c WHERE c.discussion_id = d.id
+       )
+       ORDER BY latest_activity DESC
+       LIMIT $1`,
+      [limit]
+    )
+
+    return res.json({ discussions: result.rows })
+  } catch (err) {
+    console.error('GET /explore/active error:', err)
+    res.status(500).json({ error: 'Internal server error' })
+  }
+})
+
 // ---------------------------------------------------------------------------
 // GET /explore
 // ---------------------------------------------------------------------------
diff --git a/server/routes/sitemap.js b/server/routes/sitemap.js
new file mode 100644
index 0000000..da724da
--- /dev/null
+++ b/server/routes/sitemap.js
@@ -0,0 +1,30 @@
+const express = require('express')
+const router = express.Router()
+const pool = require('../db')
+
+// GET /sitemap/discussions
+// Lightweight list for Next.js sitemap generation.
+router.get('/sitemap/discussions', async (req, res) => {
+  try {
+    const result = await pool.query(
+      `SELECT
+         d.id,
+         p.title,
+         d.created_at,
+         COALESCE(
+           (SELECT MAX(c.created_at) FROM comments c WHERE c.discussion_id = d.id),
+           d.created_at
+         ) AS last_modified
+       FROM discussions d
+       JOIN papers p ON p.id = d.paper_id
+       ORDER BY last_modified DESC`
+    )
+
+    return res.json({ discussions: result.rows })
+  } catch (err) {
+    console.error('GET /sitemap/discussions error:', err)
+    res.status(500).json({ error: 'Internal server error' })
+  }
+})
+
+module.exports = router