perf(feed): replace correlated subqueries with LEFT JOIN aggregations

Feed queries ran 5 correlated subqueries per row (3 COUNT + 2 EXISTS
for engagement counts and viewer context). Replaced with LEFT JOIN
aggregations computed once per query. Adds migration 016 with indexes
on likes(thought_id), boosts(thought_id), thoughts(in_reply_to_id),
and compound viewer-context indexes — expected to drop ~3s queries to
<100ms on typical page sizes.

Also removes WebFinger from the footer (requires query params, zero
standalone value as a link).

crates/adapters/postgres/migrations/016_engagement_indexes.sql

@@ -0,0 +1,10 @@
+-- Indexes for feed engagement counts and sorting.
+-- likes and boosts are joined/counted per thought on every feed query.
+-- thoughts(in_reply_to_id) is scanned for reply_count.
+CREATE INDEX IF NOT EXISTS idx_likes_thought_id         ON likes(thought_id);
+CREATE INDEX IF NOT EXISTS idx_boosts_thought_id        ON boosts(thought_id);
+CREATE INDEX IF NOT EXISTS idx_thoughts_in_reply_to_id  ON thoughts(in_reply_to_id) WHERE in_reply_to_id IS NOT NULL;
+
+-- Viewer-context lookups: "did I like/boost this?"
+CREATE INDEX IF NOT EXISTS idx_likes_user_thought        ON likes(user_id, thought_id);
+CREATE INDEX IF NOT EXISTS idx_boosts_user_thought       ON boosts(user_id, thought_id);

crates/adapters/postgres/src/feed/mod.rs

@@ -114,12 +114,19 @@ impl<'a> FeedSqlBuilder<'a> {
     }
 
     fn select(&self) -> String {
-        let viewer_checks = match self.viewer {
-            Some(uid) => format!(
-                "EXISTS(SELECT 1 FROM likes WHERE user_id='{uid}' AND thought_id=t.id) AS liked_by_viewer,
-                 EXISTS(SELECT 1 FROM boosts WHERE user_id='{uid}' AND thought_id=t.id) AS boosted_by_viewer"
+        let (viewer_cols, viewer_joins) = match self.viewer {
+            Some(uid) => (
+                "(lv.thought_id IS NOT NULL) AS liked_by_viewer,
+                 (bv.thought_id IS NOT NULL) AS boosted_by_viewer".to_string(),
+                format!(
+                    "LEFT JOIN (SELECT thought_id FROM likes WHERE user_id='{uid}') lv ON lv.thought_id = t.id
+                     LEFT JOIN (SELECT thought_id FROM boosts WHERE user_id='{uid}') bv ON bv.thought_id = t.id"
+                ),
+            ),
+            None => (
+                "false AS liked_by_viewer, false AS boosted_by_viewer".to_string(),
+                String::new(),
             ),
-            None => "false AS liked_by_viewer, false AS boosted_by_viewer".to_string(),
         };
         format!(
             "
@@ -143,13 +150,17 @@ impl<'a> FeedSqlBuilder<'a> {
         u.header_url, u.custom_css,
         u.local AS author_local,
         u.created_at AS author_created_at, u.updated_at AS author_updated_at,
-        (SELECT COUNT(*) FROM likes l WHERE l.thought_id=t.id) AS like_count,
-        (SELECT COUNT(*) FROM boosts b WHERE b.thought_id=t.id) AS boost_count,
-        (SELECT COUNT(*) FROM thoughts r WHERE r.in_reply_to_id=t.id) AS reply_count,
-        {viewer_checks}
+        COALESCE(l_agg.cnt, 0) AS like_count,
+        COALESCE(b_agg.cnt, 0) AS boost_count,
+        COALESCE(r_agg.cnt, 0) AS reply_count,
+        {viewer_cols}
     FROM thoughts t
     JOIN users u ON u.id=t.user_id
-    LEFT JOIN remote_actors ra ON u.ap_id = ra.url"
+    LEFT JOIN remote_actors ra ON u.ap_id = ra.url
+    LEFT JOIN (SELECT thought_id, COUNT(*) AS cnt FROM likes GROUP BY thought_id) l_agg ON l_agg.thought_id = t.id
+    LEFT JOIN (SELECT thought_id, COUNT(*) AS cnt FROM boosts GROUP BY thought_id) b_agg ON b_agg.thought_id = t.id
+    LEFT JOIN (SELECT in_reply_to_id, COUNT(*) AS cnt FROM thoughts WHERE in_reply_to_id IS NOT NULL GROUP BY in_reply_to_id) r_agg ON r_agg.in_reply_to_id = t.id
+    {viewer_joins}"
         )
     }
 

thoughts-frontend/components/footer.tsx

@@ -1,11 +1,5 @@
 import Link from "next/link";
-import {
-  BookOpen,
-  Code2,
-  Fingerprint,
-  Globe,
-  Info,
-} from "lucide-react";
+import { BookOpen, Code2, Globe, Info } from "lucide-react";
 
 const API_URL = process.env.NEXT_PUBLIC_API_URL ?? "";
 
@@ -15,30 +9,28 @@ const LINKS = [
     label: "API Reference",
     icon: BookOpen,
     external: true,
+    title: undefined,
   },
   {
     href: `${API_URL}/.well-known/nodeinfo`,
     label: "NodeInfo",
     icon: Info,
     external: true,
-  },
-  {
-    href: `${API_URL}/.well-known/webfinger`,
-    label: "WebFinger",
-    icon: Fingerprint,
-    external: true,
+    title: undefined,
   },
   {
     href: "/about/fediverse",
     label: "About the Fediverse",
     icon: Globe,
     external: false,
+    title: undefined,
   },
   {
     href: "https://git.gabrielkaszewski.dev/GKaszewski/thoughts",
     label: "Source Code",
     icon: Code2,
     external: true,
+    title: undefined,
   },
 ] as const;
 
@@ -52,7 +44,7 @@ export function Footer() {
       />
 
       <div className="container flex flex-wrap items-center justify-center gap-x-1 gap-y-2 px-4 py-3">
-        {LINKS.map(({ href, label, icon: Icon }, i) => (
+        {LINKS.map(({ href, label, icon: Icon, title }, i) => (
           <span key={href} className="flex items-center gap-1">
             {i > 0 && (
               <span className="text-muted-foreground/40 select-none text-xs mx-1">
@@ -64,6 +56,7 @@ export function Footer() {
               {...(href.startsWith("http") || href.startsWith(API_URL)
                 ? { target: "_blank", rel: "noopener noreferrer" }
                 : {})}
+              title={title}
               className="flex items-center gap-1 text-xs text-muted-foreground hover:text-primary transition-colors duration-150 group"
             >
               <Icon