diff --git a/packages/coding-agent/src/core/export-html/template.css b/packages/coding-agent/src/core/export-html/template.css
index 6ef5d3976..311af7f74 100644
--- a/packages/coding-agent/src/core/export-html/template.css
+++ b/packages/coding-agent/src/core/export-html/template.css
@@ -9,6 +9,10 @@
 
     :root {
       --line-height: 18px; /* 12px font * 1.5 */
+      --sidebar-width: 400px;
+      --sidebar-min-width: 240px;
+      --sidebar-max-width: 840px;
+      --sidebar-resizer-width: 6px;
     }
 
     body {
@@ -19,6 +23,11 @@
       background: var(--body-bg);
     }
 
+    body.sidebar-resizing {
+      cursor: col-resize;
+      user-select: none;
+    }
+
     #app {
       display: flex;
       min-height: 100vh;
@@ -26,7 +35,9 @@
 
     /* Sidebar */
     #sidebar {
-      width: 400px;
+      width: var(--sidebar-width);
+      min-width: var(--sidebar-width);
+      max-width: var(--sidebar-width);
       background: var(--container-bg);
       flex-shrink: 0;
       display: flex;
@@ -37,6 +48,24 @@
       border-right: 1px solid var(--dim);
     }
 
+    #sidebar-resizer {
+      width: var(--sidebar-resizer-width);
+      flex-shrink: 0;
+      position: sticky;
+      top: 0;
+      height: 100vh;
+      cursor: col-resize;
+      touch-action: none;
+      background: transparent;
+      border-right: 1px solid transparent;
+    }
+
+    #sidebar-resizer:hover,
+    body.sidebar-resizing #sidebar-resizer {
+      background: var(--selectedBg);
+      border-right-color: var(--dim);
+    }
+
     .sidebar-header {
       padding: 8px 12px;
       flex-shrink: 0;
@@ -213,6 +242,7 @@
     /* Main content */
     #content {
       flex: 1;
+      min-width: 0;
       overflow-y: auto;
       padding: var(--line-height) calc(var(--line-height) * 2);
       display: flex;
@@ -923,17 +953,24 @@
     @media (max-width: 900px) {
       #sidebar {
         position: fixed;
-        left: -400px;
-        width: 400px;
+        left: 0;
+        width: min(var(--sidebar-width), 100vw);
+        min-width: min(var(--sidebar-width), 100vw);
+        max-width: min(var(--sidebar-width), 100vw);
         top: 0;
         bottom: 0;
         height: 100vh;
         z-index: 99;
-        transition: left 0.3s;
+        transform: translateX(-100%);
+        transition: transform 0.3s;
       }
 
       #sidebar.open {
-        left: 0;
+        transform: translateX(0);
+      }
+
+      #sidebar-resizer {
+        display: none;
       }
 
       #sidebar-overlay.open {
@@ -957,15 +994,8 @@
       }
     }
 
-    @media (max-width: 500px) {
-      #sidebar {
-        width: 100vw;
-        left: -100vw;
-      }
-    }
-
     @media print {
-      #sidebar, #sidebar-toggle { display: none !important; }
+      #sidebar, #sidebar-resizer, #sidebar-toggle { display: none !important; }
       body { background: white; color: black; }
       #content { max-width: none; }
     }
diff --git a/packages/coding-agent/src/core/export-html/template.html b/packages/coding-agent/src/core/export-html/template.html
index 42f2a45b0..c1d678a0a 100644
--- a/packages/coding-agent/src/core/export-html/template.html
+++ b/packages/coding-agent/src/core/export-html/template.html
@@ -29,6 +29,7 @@
       <div class="tree-container" id="tree-container"></div>
       <div class="tree-status" id="tree-status"></div>
     </aside>
+    <div id="sidebar-resizer" role="separator" aria-orientation="vertical" aria-label="Resize session tree sidebar"></div>
     <main id="content">
       <div id="header-container"></div>
       <div id="messages"></div>
diff --git a/packages/coding-agent/src/core/export-html/template.js b/packages/coding-agent/src/core/export-html/template.js
index e170d7a6b..6b53516b1 100644
--- a/packages/coding-agent/src/core/export-html/template.js
+++ b/packages/coding-agent/src/core/export-html/template.js
@@ -1510,6 +1510,113 @@
       const sidebar = document.getElementById('sidebar');
       const overlay = document.getElementById('sidebar-overlay');
       const hamburger = document.getElementById('hamburger');
+      const sidebarResizer = document.getElementById('sidebar-resizer');
+      const SIDEBAR_WIDTH_STORAGE_KEY = 'pi-share:v1:sidebar-width';
+      const MIN_CONTENT_WIDTH = 320;
+
+      function isMobileLayout() {
+        return window.matchMedia('(max-width: 900px)').matches;
+      }
+
+      function getSidebarBounds() {
+        const rootStyles = getComputedStyle(document.documentElement);
+        const minWidth = parseFloat(rootStyles.getPropertyValue('--sidebar-min-width')) || 240;
+        const maxWidth = parseFloat(rootStyles.getPropertyValue('--sidebar-max-width')) || 720;
+        const viewportMaxWidth = window.innerWidth - MIN_CONTENT_WIDTH;
+        return {
+          minWidth,
+          maxWidth: Math.max(minWidth, Math.min(maxWidth, viewportMaxWidth))
+        };
+      }
+
+      function clampSidebarWidth(width) {
+        const { minWidth, maxWidth } = getSidebarBounds();
+        return Math.max(minWidth, Math.min(maxWidth, width));
+      }
+
+      function applySidebarWidth(width) {
+        document.documentElement.style.setProperty('--sidebar-width', `${Math.round(clampSidebarWidth(width))}px`);
+      }
+
+      function loadSidebarWidth() {
+        try {
+          const raw = localStorage.getItem(SIDEBAR_WIDTH_STORAGE_KEY);
+          if (raw === null) return null;
+          const width = Number(raw);
+          return Number.isFinite(width) ? width : null;
+        } catch {
+          return null;
+        }
+      }
+
+      function saveSidebarWidth(width) {
+        try {
+          localStorage.setItem(SIDEBAR_WIDTH_STORAGE_KEY, String(Math.round(clampSidebarWidth(width))));
+        } catch {
+          // Ignore storage failures (e.g. private browsing restrictions)
+        }
+      }
+
+      function setupSidebarResize() {
+        const savedWidth = loadSidebarWidth();
+        if (savedWidth !== null) {
+          applySidebarWidth(savedWidth);
+        }
+
+        if (!sidebarResizer) return;
+
+        let cleanupDrag = null;
+
+        const stopDrag = (pointerId) => {
+          if (cleanupDrag) {
+            cleanupDrag(pointerId);
+            cleanupDrag = null;
+          }
+        };
+
+        sidebarResizer.addEventListener('pointerdown', (e) => {
+          if (isMobileLayout()) return;
+
+          e.preventDefault();
+          const startX = e.clientX;
+          const startWidth = sidebar.getBoundingClientRect().width;
+          document.body.classList.add('sidebar-resizing');
+          sidebarResizer.setPointerCapture?.(e.pointerId);
+
+          const onPointerMove = (event) => {
+            applySidebarWidth(startWidth + (event.clientX - startX));
+          };
+
+          cleanupDrag = (pointerIdToRelease) => {
+            document.body.classList.remove('sidebar-resizing');
+            sidebarResizer.releasePointerCapture?.(pointerIdToRelease);
+            window.removeEventListener('pointermove', onPointerMove);
+            window.removeEventListener('pointerup', onPointerUp);
+            window.removeEventListener('pointercancel', onPointerCancel);
+            saveSidebarWidth(sidebar.getBoundingClientRect().width);
+          };
+
+          const onPointerUp = (event) => stopDrag(event.pointerId);
+          const onPointerCancel = (event) => stopDrag(event.pointerId);
+
+          window.addEventListener('pointermove', onPointerMove);
+          window.addEventListener('pointerup', onPointerUp);
+          window.addEventListener('pointercancel', onPointerCancel);
+        });
+
+        sidebarResizer.addEventListener('dblclick', () => {
+          if (isMobileLayout()) return;
+          applySidebarWidth(400);
+          saveSidebarWidth(400);
+        });
+
+        window.addEventListener('resize', () => {
+          if (isMobileLayout()) return;
+          applySidebarWidth(sidebar.getBoundingClientRect().width);
+        });
+      }
+
+      setupSidebarResize();
 
       hamburger.addEventListener('click', () => {
         sidebar.classList.add('open');