diff --git a/dist/js/docsView.js b/dist/js/docsView.js
index 59a37fc9..77475204 100644
--- a/dist/js/docsView.js
+++ b/dist/js/docsView.js
@@ -29,6 +29,8 @@ const scrollSpyState = {
   activeId: "",
   rafId: null,
   onScroll: null,
+  observer: null,
+  passedHeadings: null,
 };
 
 function getHashParams() {
@@ -260,15 +262,11 @@ function resetSectionHighlight() {
 }
 
 function clearScrollSpy() {
-  if (scrollSpyState.onScroll && typeof window !== "undefined") {
-    window.removeEventListener("scroll", scrollSpyState.onScroll);
-    window.removeEventListener("resize", scrollSpyState.onScroll);
+  if (scrollSpyState.observer) {
+    scrollSpyState.observer.disconnect();
+    scrollSpyState.observer = null;
   }
-  if (scrollSpyState.rafId && typeof cancelAnimationFrame === "function") {
-    cancelAnimationFrame(scrollSpyState.rafId);
-  }
-  scrollSpyState.rafId = null;
-  scrollSpyState.onScroll = null;
+  scrollSpyState.passedHeadings = null;
   scrollSpyState.headings = [];
   scrollSpyState.linkLookup = new Map();
   resetSectionHighlight();
@@ -328,6 +326,7 @@ function setupScrollSpy(container) {
   const headings = Array.from(
     container.querySelectorAll("h2[id], h3[id], h4[id], h5[id]")
   );
+  console.log(`[Spy] setup found ${headings.length} headings`);
   if (headings.length === 0) {
     return;
   }
@@ -345,34 +344,56 @@ function setupScrollSpy(container) {
   scrollSpyState.headings = trackedHeadings;
   scrollSpyState.linkLookup = linkLookup;
 
-  const updateActiveFromScroll = () => {
-    scrollSpyState.rafId = null;
-    const offset = 96;
-    let nextId = scrollSpyState.headings[0]?.id || "";
-    for (const heading of scrollSpyState.headings) {
-      const top = heading.getBoundingClientRect().top - offset;
-      if (top <= 0) {
-        nextId = heading.id;
+  const observerCallback = (entries) => {
+    const passed = scrollSpyState.passedHeadings || new Set();
+
+    entries.forEach((entry) => {
+      // If the heading intersects (enters the viewport from top or bottom),
+      // we check if it is above the offset.
+      if (entry.isIntersecting) {
+        // If it is intersecting, it is definitely "visible" in the viewport (minus top margin).
+        // It means it's not "passed" (above the top).
+        passed.delete(entry.target.id);
       } else {
+        // If not intersecting, check if it's above.
+        // rootMargin top is -96px. The root starts at 96px from top.
+        // If entry.boundingClientRect.top < 96, it is above the root.
+        if (entry.boundingClientRect.top < 96) {
+          passed.add(entry.target.id);
+        } else {
+          passed.delete(entry.target.id);
+        }
+      }
+    });
+
+    scrollSpyState.passedHeadings = passed;
+
+    let nextId = "";
+    // Find the last heading in the passed set (by DOM order)
+    for (let i = scrollSpyState.headings.length - 1; i >= 0; i--) {
+      const id = scrollSpyState.headings[i].id;
+      if (passed.has(id)) {
+        nextId = id;
         break;
       }
     }
+    // Fallback to the first heading if none are passed yet (scrolled to top)
+    if (!nextId && scrollSpyState.headings.length > 0) {
+      nextId = scrollSpyState.headings[0].id;
+    }
+
     if (nextId) {
       setActiveSection(nextId);
     }
   };
 
-  const onScroll = () => {
-    if (scrollSpyState.rafId) {
-      return;
-    }
-    scrollSpyState.rafId = requestAnimationFrame(updateActiveFromScroll);
-  };
+  const observer = new IntersectionObserver(observerCallback, {
+    rootMargin: "-96px 0px 0px 0px",
+    threshold: 0,
+  });
 
-  scrollSpyState.onScroll = onScroll;
-  window.addEventListener("scroll", onScroll, { passive: true });
-  window.addEventListener("resize", onScroll);
-  onScroll();
+  scrollSpyState.headings.forEach((heading) => observer.observe(heading));
+  scrollSpyState.observer = observer;
 }
 
 function resolveDocItem(slug) {
diff --git a/dist/js/feedEngine/sorters.js b/dist/js/feedEngine/sorters.js
index c4620509..f4b1e9e8 100644
--- a/dist/js/feedEngine/sorters.js
+++ b/dist/js/feedEngine/sorters.js
@@ -301,6 +301,13 @@ export function createExploreDiversitySorter({
     const selected = [];
     const remaining = [...candidates];
 
+    // Cache max similarity for each remaining candidate against the selected set
+    // Map<CandidateItem, { penalty: number, similarItemId: string }>
+    const similarityCache = new Map();
+    for (const candidate of remaining) {
+      similarityCache.set(candidate, { penalty: 0, similarItemId: "" });
+    }
+
     while (remaining.length > 0) {
       let bestCandidate = null;
       let bestMmr = Number.NEGATIVE_INFINITY;
@@ -326,22 +333,7 @@ export function createExploreDiversitySorter({
 
       for (const candidate of remaining) {
         const rawScore = normalizeScore(candidate?.metadata?.exploreScore);
-        let penalty = 0;
-        let similarItemId = "";
-
-        if (selected.length > 0) {
-          const candidateVector = vectors.get(candidate);
-          for (const selectedItem of selected) {
-            const similarity = cosineSimilarity(
-              candidateVector,
-              vectors.get(selectedItem),
-            );
-            if (similarity > penalty) {
-              penalty = similarity;
-              similarItemId = stableVideoId(selectedItem);
-            }
-          }
-        }
+        const { penalty, similarItemId } = similarityCache.get(candidate);
 
         const mmrScore =
           normalizedLambda * rawScore - (1 - normalizedLambda) * penalty;
@@ -404,6 +396,22 @@ export function createExploreDiversitySorter({
       const index = remaining.indexOf(bestCandidate);
       if (index >= 0) {
         remaining.splice(index, 1);
+        similarityCache.delete(bestCandidate);
+      }
+
+      // Update similarity cache for remaining candidates against the newly selected item
+      const bestCandidateVector = vectors.get(bestCandidate);
+      for (const candidate of remaining) {
+        const candidateVector = vectors.get(candidate);
+        const similarity = cosineSimilarity(
+          candidateVector,
+          bestCandidateVector,
+        );
+        const cache = similarityCache.get(candidate);
+        if (similarity > cache.penalty) {
+          cache.penalty = similarity;
+          cache.similarItemId = stableVideoId(bestCandidate);
+        }
       }
     }
 
diff --git a/dist/js/state/profileCache.js b/dist/js/state/profileCache.js
index eacf26f4..1fd3e253 100644
--- a/dist/js/state/profileCache.js
+++ b/dist/js/state/profileCache.js
@@ -26,7 +26,7 @@ function sanitizeProfileString(value) {
 class ProfileCache {
   constructor() {
     this.activePubkey = null;
-    this.memoryCache = new Map(); // For runtime decrypted data: pubkey:section -> data
+    this.memoryCache = new Map(); // For runtime decrypted data: pubkey -> Map(section -> data)
     this.listeners = new Set();
   }
 
@@ -240,9 +240,11 @@ class ProfileCache {
 
   getProfileData(pubkey, section) {
     // 1. Check memory cache (runtime data)
-    const memKey = `${pubkey}:${section}`;
-    if (this.memoryCache.has(memKey)) {
-      return this.memoryCache.get(memKey);
+    if (this.memoryCache.has(pubkey)) {
+      const userCache = this.memoryCache.get(pubkey);
+      if (userCache.has(section)) {
+        return userCache.get(section);
+      }
     }
 
     // 2. Load from persistence
@@ -273,7 +275,10 @@ class ProfileCache {
           }
 
           // Populate memory cache to avoid repeat parsing
-          this.memoryCache.set(memKey, parsed);
+          if (!this.memoryCache.has(pubkey)) {
+            this.memoryCache.set(pubkey, new Map());
+          }
+          this.memoryCache.get(pubkey).set(section, parsed);
           return parsed;
         }
       } catch (error) {
@@ -302,39 +307,42 @@ class ProfileCache {
     }
 
     // Update memory cache
-    const memKey = `${pubkey}:${section}`;
-    this.memoryCache.set(memKey, data);
+    if (!this.memoryCache.has(pubkey)) {
+      this.memoryCache.set(pubkey, new Map());
+    }
+    this.memoryCache.get(pubkey).set(section, data);
 
     this.emit("update", { pubkey, section, data });
     this.emit("partition-updated", { pubkey, key: section });
   }
 
   setMemoryDataForPubkey(pubkey, section, data) {
-    const memKey = `${pubkey}:${section}`;
-    this.memoryCache.set(memKey, data);
+    if (!this.memoryCache.has(pubkey)) {
+      this.memoryCache.set(pubkey, new Map());
+    }
+    this.memoryCache.get(pubkey).set(section, data);
+
     this.emit("update", { pubkey, section, data });
   }
 
   setMemoryData(section, data) {
     if (!this.activePubkey) return;
-    const key = `${this.activePubkey}:${section}`;
-    this.memoryCache.set(key, data);
+    if (!this.memoryCache.has(this.activePubkey)) {
+      this.memoryCache.set(this.activePubkey, new Map());
+    }
+    this.memoryCache.get(this.activePubkey).set(section, data);
   }
 
   getMemoryData(section) {
     if (!this.activePubkey) return null;
-    const key = `${this.activePubkey}:${section}`;
-    return this.memoryCache.get(key);
+    if (this.memoryCache.has(this.activePubkey)) {
+      return this.memoryCache.get(this.activePubkey).get(section);
+    }
+    return undefined;
   }
 
   clearMemoryCache(pubkey) {
-    // Clear all entries starting with pubkey:
-    const prefix = `${pubkey}:`;
-    for (const key of this.memoryCache.keys()) {
-      if (key.startsWith(prefix)) {
-        this.memoryCache.delete(key);
-      }
-    }
+    this.memoryCache.delete(pubkey);
   }
 
   clearSignerRuntime(pubkey) {
diff --git a/js/docsView.js b/js/docsView.js
index 59a37fc9..1df499b7 100644
--- a/js/docsView.js
+++ b/js/docsView.js
@@ -29,6 +29,8 @@ const scrollSpyState = {
   activeId: "",
   rafId: null,
   onScroll: null,
+  observer: null,
+  passedHeadings: null,
 };
 
 function getHashParams() {
@@ -260,15 +262,11 @@ function resetSectionHighlight() {
 }
 
 function clearScrollSpy() {
-  if (scrollSpyState.onScroll && typeof window !== "undefined") {
-    window.removeEventListener("scroll", scrollSpyState.onScroll);
-    window.removeEventListener("resize", scrollSpyState.onScroll);
+  if (scrollSpyState.observer) {
+    scrollSpyState.observer.disconnect();
+    scrollSpyState.observer = null;
   }
-  if (scrollSpyState.rafId && typeof cancelAnimationFrame === "function") {
-    cancelAnimationFrame(scrollSpyState.rafId);
-  }
-  scrollSpyState.rafId = null;
-  scrollSpyState.onScroll = null;
+  scrollSpyState.passedHeadings = null;
   scrollSpyState.headings = [];
   scrollSpyState.linkLookup = new Map();
   resetSectionHighlight();
@@ -345,34 +343,56 @@ function setupScrollSpy(container) {
   scrollSpyState.headings = trackedHeadings;
   scrollSpyState.linkLookup = linkLookup;
 
-  const updateActiveFromScroll = () => {
-    scrollSpyState.rafId = null;
-    const offset = 96;
-    let nextId = scrollSpyState.headings[0]?.id || "";
-    for (const heading of scrollSpyState.headings) {
-      const top = heading.getBoundingClientRect().top - offset;
-      if (top <= 0) {
-        nextId = heading.id;
+  const observerCallback = (entries) => {
+    const passed = scrollSpyState.passedHeadings || new Set();
+
+    entries.forEach((entry) => {
+      // If the heading intersects (enters the viewport from top or bottom),
+      // we check if it is above the offset.
+      if (entry.isIntersecting) {
+        // If it is intersecting, it is definitely "visible" in the viewport (minus top margin).
+        // It means it's not "passed" (above the top).
+        passed.delete(entry.target.id);
       } else {
+        // If not intersecting, check if it's above.
+        // rootMargin top is -96px. The root starts at 96px from top.
+        // If entry.boundingClientRect.top < 96, it is above the root.
+        if (entry.boundingClientRect.top < 96) {
+          passed.add(entry.target.id);
+        } else {
+          passed.delete(entry.target.id);
+        }
+      }
+    });
+
+    scrollSpyState.passedHeadings = passed;
+
+    let nextId = "";
+    // Find the last heading in the passed set (by DOM order)
+    for (let i = scrollSpyState.headings.length - 1; i >= 0; i--) {
+      const id = scrollSpyState.headings[i].id;
+      if (passed.has(id)) {
+        nextId = id;
         break;
       }
     }
+    // Fallback to the first heading if none are passed yet (scrolled to top)
+    if (!nextId && scrollSpyState.headings.length > 0) {
+      nextId = scrollSpyState.headings[0].id;
+    }
+
     if (nextId) {
       setActiveSection(nextId);
     }
   };
 
-  const onScroll = () => {
-    if (scrollSpyState.rafId) {
-      return;
-    }
-    scrollSpyState.rafId = requestAnimationFrame(updateActiveFromScroll);
-  };
+  const observer = new IntersectionObserver(observerCallback, {
+    rootMargin: "-96px 0px 0px 0px",
+    threshold: 0,
+  });
 
-  scrollSpyState.onScroll = onScroll;
-  window.addEventListener("scroll", onScroll, { passive: true });
-  window.addEventListener("resize", onScroll);
-  onScroll();
+  scrollSpyState.headings.forEach((heading) => observer.observe(heading));
+  scrollSpyState.observer = observer;
 }
 
 function resolveDocItem(slug) {