diff --git a/src/server/services/html-exporter.ts b/src/server/services/html-exporter.ts
index 77c1177..c591e6a 100644
--- a/src/server/services/html-exporter.ts
+++ b/src/server/services/html-exporter.ts
@@ -1,7 +1,7 @@
 import { marked } from "marked";
 import hljs from "highlight.js";
 import { markedHighlight } from "marked-highlight";
-import type { ExportRequest, ParsedMessage } from "../../shared/types.js";
+import type { ExportRequest, ParsedMessage, ProgressSubtype } from "../../shared/types.js";
 import { CATEGORY_LABELS } from "../../shared/types.js";
 import { redactMessage } from "../../shared/sensitive-redactor.js";
 import { escapeHtml } from "../../shared/escape-html.js";
@@ -22,7 +22,11 @@ marked.use(
 
 // Categories whose content is structured data (JSON, logs, snapshots) — not markdown.
 // Rendered as preformatted text to avoid the cost of markdown parsing on large blobs.
-const PREFORMATTED_CATEGORIES = new Set(["hook_progress", "tool_result", "file_snapshot"]);
+// Note: tool_result is handled explicitly in renderMessage() for diff detection.
+const PREFORMATTED_CATEGORIES = new Set(["hook_progress", "file_snapshot"]);
+
+// Categories that render collapsed by default
+const COLLAPSIBLE_CATEGORIES = new Set(["thinking", "tool_call", "tool_result"]);
 
 // Category dot/border colors matching the client-side design
 const CATEGORY_STYLES: Record<string, { dot: string; border: string; text: string }> = {
@@ -37,10 +41,19 @@ const CATEGORY_STYLES: Record<string, { dot: string; border: string; text: strin
   summary:        { dot: "#2dd4bf", border: "#1a4d45", text: "#2dd4bf" },
 };
 
+// Progress subtype colors for the export badge pills
+const PROGRESS_SUBTYPE_COLORS: Record<ProgressSubtype, { text: string; bg: string }> = {
+  hook:  { text: "#484f58", bg: "rgba(72,79,88,0.1)" },
+  bash:  { text: "#d29922", bg: "rgba(210,153,34,0.1)" },
+  mcp:   { text: "#8b8cf8", bg: "rgba(139,140,248,0.1)" },
+  agent: { text: "#bc8cff", bg: "rgba(188,140,255,0.1)" },
+};
+
 export async function generateExportHtml(
   req: ExportRequest
 ): Promise<string> {
   const { session, visibleMessageUuids, redactedMessageUuids, autoRedactEnabled } = req;
+  const toolProgress = session.toolProgress || {};
 
   const visibleSet = new Set(visibleMessageUuids);
   const redactedSet = new Set(redactedMessageUuids);
@@ -65,7 +78,8 @@ export async function generateExportHtml(
       lastWasRedacted = false;
     }
     const msgToRender = autoRedactEnabled ? redactMessage(msg) : msg;
-    messageHtmlParts.push(renderMessage(msgToRender));
+    const progressEvents = msg.toolUseId ? toolProgress[msg.toolUseId] : undefined;
+    messageHtmlParts.push(renderMessage(msgToRender, progressEvents));
   }
 
   const hljsCss = getHighlightCss();
@@ -100,7 +114,7 @@ ${hljsCss}
       </span>
       <span class="meta-item">
         <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"><path d="M7.5 8.25h9m-9 3H12m-9.75 1.51c0 1.6 1.123 2.994 2.707 3.227 1.129.166 2.27.293 3.423.379.35.026.67.21.865.501L12 21l2.755-4.133a1.14 1.14 0 01.865-.501 48.172 48.172 0 003.423-.379c1.584-.233 2.707-1.626 2.707-3.228V6.741c0-1.602-1.123-2.995-2.707-3.228A48.394 48.394 0 0012 3c-2.392 0-4.744.175-7.043.513C3.373 3.746 2.25 5.14 2.25 6.741v6.018z"/></svg>
-        ${messageCount} message${messageCount !== 1 ? "s" : ""} 
+        ${messageCount} message${messageCount !== 1 ? "s" : ""}
       </span>
     </div>
   </header>
@@ -108,6 +122,9 @@ ${hljsCss}
     ${messageHtmlParts.join("\n    ")}
   </main>
 </div>
+<script>
+${getExportJs()}
+</script>
 </body>
 </html>`;
 }
@@ -123,9 +140,11 @@ function renderRedactedDivider(): string {
 </div>`;
 }
 
-function renderMessage(msg: ParsedMessage): string {
+function renderMessage(msg: ParsedMessage, progressEvents?: ParsedMessage[]): string {
   const style = CATEGORY_STYLES[msg.category] || CATEGORY_STYLES.system_message;
   const label = CATEGORY_LABELS[msg.category];
+  const isCollapsible = COLLAPSIBLE_CATEGORIES.has(msg.category);
+
   let bodyHtml: string;
 
   if (msg.category === "tool_call") {
@@ -133,10 +152,11 @@ function renderMessage(msg: ParsedMessage): string {
       ? `<pre class="hljs"><code>${escapeHtml(msg.toolInput)}</code></pre>`
       : "";
     bodyHtml = `<div class="tool-name" style="color: ${style.text}">${escapeHtml(msg.toolName || "Unknown Tool")}</div>${inputHtml}`;
+  } else if (msg.category === "tool_result") {
+    bodyHtml = isDiffContent(msg.content)
+      ? renderDiffHtml(msg.content)
+      : `<pre class="hljs"><code>${escapeHtml(msg.content)}</code></pre>`;
   } else if (PREFORMATTED_CATEGORIES.has(msg.category)) {
-    // These categories contain structured data (JSON, logs, snapshots), not prose.
-    // Rendering them through marked is both incorrect and extremely slow on large
-    // content (370KB JSON blobs take ~300ms each in marked.parse).
     bodyHtml = `<pre class="hljs"><code>${escapeHtml(msg.content)}</code></pre>`;
   } else {
     bodyHtml = renderMarkdown(msg.content);
@@ -147,16 +167,119 @@ function renderMessage(msg: ParsedMessage): string {
     ? `<span class="header-sep">&middot;</span><span class="message-time">${escapeHtml(timestamp)}</span>`
     : "";
 
-  return `<div class="message" style="border-color: ${style.border}">
+  // Build collapsed preview for collapsible categories
+  let previewHtml = "";
+  if (isCollapsible) {
+    let previewText: string;
+    if (msg.category === "thinking") {
+      const lineCount = msg.content.split("\n").filter(l => l.trim()).length;
+      previewText = `${lineCount} line${lineCount !== 1 ? "s" : ""}`;
+    } else if (msg.category === "tool_call") {
+      previewText = msg.toolName || "Unknown Tool";
+    } else {
+      // tool_result — first 120 chars of first line
+      previewText = (msg.content.split("\n")[0] || "Result").substring(0, 120);
+    }
+    previewHtml = `<span class="header-sep">&middot;</span><span class="collapsed-preview">${escapeHtml(previewText)}</span>`;
+  }
+
+  // Chevron toggle button for collapsible messages
+  const chevronHtml = isCollapsible
+    ? `<button class="collapsible-toggle" aria-label="Toggle"><svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round"><path d="M8.25 4.5l7.5 7.5-7.5 7.5"/></svg></button>`
+    : "";
+
+  const dataAttrs = isCollapsible ? ' data-collapsed="true"' : "";
+
+  // Progress badge for tool_call messages
+  const progressHtml = (msg.category === "tool_call" && progressEvents && progressEvents.length > 0)
+    ? renderProgressBadge(progressEvents)
+    : "";
+
+  return `<div class="message"${dataAttrs} style="border-color: ${style.border}">
   <div class="message-header">
-    <span class="message-dot" style="background: ${style.dot}"></span>
+    ${chevronHtml}<span class="message-dot" style="background: ${style.dot}"></span>
     <span class="message-label">${escapeHtml(label)}</span>
     ${timestampHtml}
+    ${previewHtml}
   </div>
   <div class="message-body prose-message">${bodyHtml}</div>
+  ${progressHtml}
 </div>`;
 }
 
+function isDiffContent(content: string): boolean {
+  const lines = content.split("\n").slice(0, 30);
+  let hunkHeaders = 0;
+  let diffLines = 0;
+  for (const line of lines) {
+    if (line.startsWith("@@") || line.startsWith("diff --")) {
+      hunkHeaders++;
+    } else if (line.startsWith("+++") || line.startsWith("---")) {
+      hunkHeaders++;
+    } else if (line.startsWith("+") || line.startsWith("-")) {
+      diffLines++;
+    }
+  }
+  return hunkHeaders >= 1 && diffLines >= 2;
+}
+
+function renderDiffHtml(content: string): string {
+  const lines = content.split("\n");
+  const htmlLines = lines.map((line) => {
+    const escaped = escapeHtml(line);
+    if (line.startsWith("@@")) {
+      return `<span class="diff-hunk">${escaped}</span>`;
+    }
+    if (line.startsWith("+++") || line.startsWith("---")) {
+      return `<span class="diff-meta">${escaped}</span>`;
+    }
+    if (line.startsWith("diff --")) {
+      return `<span class="diff-header">${escaped}</span>`;
+    }
+    if (line.startsWith("+")) {
+      return `<span class="diff-add">${escaped}</span>`;
+    }
+    if (line.startsWith("-")) {
+      return `<span class="diff-del">${escaped}</span>`;
+    }
+    return escaped;
+  });
+  return `<pre class="hljs diff-view"><code>${htmlLines.join("\n")}</code></pre>`;
+}
+
+function renderProgressBadge(events: ParsedMessage[]): string {
+  // Count by subtype
+  const counts: Partial<Record<ProgressSubtype, number>> = {};
+  for (const e of events) {
+    const sub = e.progressSubtype || "hook";
+    counts[sub] = (counts[sub] || 0) + 1;
+  }
+
+  // Pill row
+  const pills = (Object.entries(counts) as [ProgressSubtype, number][])
+    .map(([sub, count]) => {
+      const colors = PROGRESS_SUBTYPE_COLORS[sub] || PROGRESS_SUBTYPE_COLORS.hook;
+      return `<span class="progress-pill" style="color:${colors.text};background:${colors.bg}">${escapeHtml(sub)}: ${count}</span>`;
+    })
+    .join("");
+
+  // Drawer rows
+  const rows = events
+    .map((e) => {
+      const time = e.timestamp ? formatTimestamp(e.timestamp) : "--:--:--";
+      const sub = e.progressSubtype || "hook";
+      return `<div class="progress-row"><span class="progress-time">${escapeHtml(time)}</span><span class="progress-subtype">${escapeHtml(sub)}</span><span class="progress-content">${escapeHtml(e.content)}</span></div>`;
+    })
+    .join("\n      ");
+
+  return `<div class="progress-badge">
+    <button class="progress-toggle">${pills}</button>
+    <div class="progress-drawer" style="display:none">
+      ${rows}
+    </div>
+  </div>`;
+}
+
 // marked.parse() is called synchronously here. In marked v14+ it can return
 // Promise<string> if async extensions are configured. Our markedHighlight setup
 // is synchronous, so the cast is safe — but do not add async extensions without
@@ -179,6 +302,28 @@ function formatTimestamp(ts: string): string {
   });
 }
 
+function getExportJs(): string {
+  return `
+document.addEventListener("click", function(e) {
+  var toggle = e.target.closest(".collapsible-toggle");
+  if (toggle) {
+    var msg = toggle.closest(".message");
+    if (!msg) return;
+    var collapsed = msg.getAttribute("data-collapsed") === "true";
+    msg.setAttribute("data-collapsed", collapsed ? "false" : "true");
+    return;
+  }
+  var progressToggle = e.target.closest(".progress-toggle");
+  if (progressToggle) {
+    var drawer = progressToggle.nextElementSibling;
+    if (drawer && drawer.classList.contains("progress-drawer")) {
+      drawer.style.display = drawer.style.display === "none" ? "block" : "none";
+    }
+  }
+});
+`;
+}
+
 function getHighlightCss(): string {
   // Dark theme highlight.js (GitHub Dark) matching the client
   return `
@@ -259,6 +404,19 @@ body {
   border-radius: 0.75rem;
   border: 1px solid #30363d;
   box-shadow: 0 1px 3px 0 rgb(0 0 0 / 0.3);
+  position: relative;
+  overflow: hidden;
+}
+.message::before {
+  content: "";
+  position: absolute;
+  left: 0;
+  top: 0;
+  bottom: 0;
+  width: 3px;
+  border-radius: 0.75rem 0 0 0.75rem;
+  background: currentColor;
+  opacity: 0.5;
 }
 .message-header {
   display: flex;
@@ -298,6 +456,97 @@ body {
   line-height: 1.5rem;
 }
 
+/* Collapsible toggle */
+.collapsible-toggle {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 1.25rem;
+  height: 1.25rem;
+  background: none;
+  border: none;
+  color: #484f58;
+  cursor: pointer;
+  padding: 0;
+  flex-shrink: 0;
+  transition: color 0.15s, transform 0.15s;
+}
+.collapsible-toggle:hover { color: #e6edf3; }
+.message[data-collapsed="false"] .collapsible-toggle svg { transform: rotate(90deg); }
+.message[data-collapsed="true"] .message-body { display: none; }
+.collapsed-preview {
+  font-size: 0.75rem;
+  color: #484f58;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  max-width: 300px;
+}
+
+/* Diff highlighting */
+.diff-view { font-size: 0.8125rem; line-height: 1.6; }
+.diff-add { color: #7ee787; background: rgba(46,160,67,0.15); display: block; }
+.diff-del { color: #ffa198; background: rgba(248,81,73,0.15); display: block; }
+.diff-hunk { color: #bc8cff; display: block; }
+.diff-meta { color: #8b949e; display: block; }
+.diff-header { color: #e6edf3; font-weight: 600; display: block; }
+
+/* Progress badge */
+.progress-badge {
+  padding: 0.25rem 1rem 0.75rem;
+}
+.progress-toggle {
+  display: flex;
+  align-items: center;
+  gap: 0.375rem;
+  background: none;
+  border: none;
+  cursor: pointer;
+  padding: 0;
+  font-size: 0.6875rem;
+}
+.progress-pill {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.25rem;
+  padding: 0.125rem 0.375rem;
+  border-radius: 0.25rem;
+  font-family: "JetBrains Mono", "Fira Code", monospace;
+  font-size: 0.6875rem;
+}
+.progress-drawer {
+  margin-top: 0.5rem;
+  padding: 0.5rem;
+  background: #161b22;
+  border: 1px solid #21262d;
+  border-radius: 0.5rem;
+}
+.progress-row {
+  display: flex;
+  gap: 0.5rem;
+  font-family: "JetBrains Mono", "Fira Code", monospace;
+  font-size: 0.6875rem;
+  line-height: 1.4;
+  padding: 0.125rem 0;
+}
+.progress-time {
+  width: 5rem;
+  flex-shrink: 0;
+  color: #484f58;
+  font-variant-numeric: tabular-nums;
+}
+.progress-subtype {
+  width: 3.5rem;
+  flex-shrink: 0;
+  font-weight: 500;
+}
+.progress-content {
+  flex: 1;
+  min-width: 0;
+  overflow-wrap: break-word;
+  color: #8b949e;
+}
+
 /* Tool name */
 .tool-name { font-weight: 500; margin-bottom: 0.5rem; }
 
@@ -405,6 +654,10 @@ body {
   body { background: #1c2128; }
   .session-export { padding: 0; max-width: 100%; }
   .session-header, .message { box-shadow: none; break-inside: avoid; }
+  .message-body { display: block !important; }
+  .collapsed-preview { display: none !important; }
+  .collapsible-toggle { display: none !important; }
+  .progress-drawer { display: block !important; }
 }
 `;
 }