diff --git a/CHANGELOG.md b/CHANGELOG.md
index 03208f7..eb34210 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,4 @@
+2026-08-26 13:12 UTC — Add course outline sidebar to the lesson page
 2026-08-25 12:25 UTC — Remove unreliable duplicate-lesson-file matching
 2026-08-25 00:33 UTC — Widen thumbnail sampling window past platform bumpers
 2026-08-25 00:26 UTC — Fix race condition in thumbnail candidate generation
diff --git a/README.md b/README.md
index 142fcbc..59d3b55 100644
--- a/README.md
+++ b/README.md
@@ -225,6 +225,14 @@ silently stay blank instead of erroring.
 **Playback & progress**
 - Video/audio player with resize, playback-speed presets, and resume-from-
   last-position
+- Course outline sidebar on the lesson page: every section and lesson in
+  the course (videos and documents alike - a standalone PDF/doc is its own
+  entry, same as a video), one click to jump anywhere without backing out
+  to the course page first. The current lesson's section opens
+  automatically and scrolls into view; sticky and independently
+  scrollable on desktop, stacks below the player on narrow viewports.
+  Shares its rendering with the loaded-course dashboard view (`templates/
+  _course_tree.html`), so the two always look and behave the same.
 - Auto-play next lesson when one ends, with a cancelable few-second
   countdown - on by default, toggle it off in Settings → Video Player
 - Keyboard shortcuts on the lesson page: Space (play/pause), ←/→ (seek
diff --git a/VERSION b/VERSION
index 8658d3e..159c086 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2026-08-25 12:25 UTC — remove unreliable duplicate-lesson-file matching
+2026-08-26 13:12 UTC — add course outline sidebar to the lesson page
diff --git a/offlineu_core.py b/offlineu_core.py
index c0bb4ae..48fc718 100644
--- a/offlineu_core.py
+++ b/offlineu_core.py
@@ -4554,8 +4554,16 @@ def view_lesson(lesson_path: str):
     if not current_course:
         return redirect(url_for('index'))
 
-    # Find the lesson in the tree, and the section (DirectoryNode) it belongs to
-    lesson, section_node = find_lesson_in_tree(current_course.root_node, lesson_path)
+    # Populates the whole tree's Lesson objects (completed/progress_seconds/
+    # duration_seconds) from disk - needed for the course-outline sidebar,
+    # which (like the dashboard's tree) reads those fields directly rather
+    # than loading progress per-row.
+    ProgressTracker.apply_progress_to_tree(current_course)
+
+    # Find the lesson in the tree (the section/DirectoryNode it belongs to
+    # isn't needed here anymore - the sidebar shows the whole course, not
+    # just this lesson's own section)
+    lesson, _ = find_lesson_in_tree(current_course.root_node, lesson_path)
 
     if not lesson:
         return redirect(url_for('index'))
@@ -4603,7 +4611,6 @@ def view_lesson(lesson_path: str):
                            initial_seek_seconds=seek_seconds,
                            outline_topic_id=lesson_progress.get('outline_topic_id', ''),
                            outline_topic_name=lesson_progress.get('outline_topic_name', ''),
-                           section_lessons=get_section_lessons(current_course, section_node, lesson),
                            prev_lesson=prev_lesson,
                            next_lesson=next_lesson)
 
@@ -4656,36 +4663,6 @@ def find_lesson_in_tree(node: DirectoryNode, target_path: str) -> Tuple[Optional
     return None, None
 
 
-def get_section_lessons(course: Course, section_node: DirectoryNode, current_lesson: Lesson) -> List[Dict[str, Any]]:
-    """
-    The sibling lessons in current_lesson's own section, for the lesson
-    page's "up next in this section" list. view_lesson() isn't on the
-    apply_progress_to_tree() code path, so - like that route already does
-    for the current lesson's own notes/progress - this reads progress
-    directly from the progress file rather than relying on Lesson fields.
-    """
-    progress = ProgressTracker.load_progress(course)
-    siblings = []
-    for sibling in section_node.lessons:
-        key = _resolve_lesson_progress_key(course, sibling, progress)
-        entry = progress.get(key, {}) if key else {}
-        completed = entry.get('completed', False)
-        progress_seconds = entry.get('progress_seconds', 0)
-        duration_seconds = entry.get('duration_seconds', 0)
-        percent_watched = 100 if completed else (
-            round(100 * progress_seconds / duration_seconds) if duration_seconds and progress_seconds else 0
-        )
-        siblings.append({
-            'title': sibling.title,
-            'url': get_lesson_url(sibling, course.path),
-            'lesson_type': sibling.lesson_type,
-            'completed': completed,
-            'percent_watched': percent_watched,
-            'is_current': sibling is current_lesson,
-        })
-    return siblings
-
-
 def get_all_lessons(node: DirectoryNode) -> List[Tuple[str, Lesson]]:
     """Get all lessons from the tree with their paths"""
     lessons = []
diff --git a/templates/_course_tree.html b/templates/_course_tree.html
new file mode 100644
index 0000000..9f5120e
--- /dev/null
+++ b/templates/_course_tree.html
@@ -0,0 +1,78 @@
+{% import '_icons.html' as icons %}
+{#
+    Shared recursive course-outline renderer - one section/lesson tree
+    markup used by both the loaded-course dashboard view and the lesson
+    page's sidebar, so the two stay visually and behaviorally in sync
+    instead of drifting apart as separate copies. Needs `toggleTree()`
+    (JS) and the .tree-*/.lesson-*/.status-icon/.watched-badge CSS to be
+    defined by whichever page imports this - see course_dashboard.html
+    for the canonical versions.
+
+    `current_lesson` (a Lesson object, not a path string) is optional -
+    when given, the matching row gets a `current` class instead of being
+    a plain click target, and stays unclickable since you're already
+    there. Path-string comparison isn't used for this because the lesson
+    page's incoming URL can be in several different formats (see
+    find_lesson_in_tree) - comparing lesson.path (the raw absolute
+    filesystem path, always unique and unambiguous) sidesteps all of that.
+#}
+{% macro render_tree_node(node, course_path, current_lesson=none, depth=0) %}
+{% set stats = section_stats(node) %}
+<div class="tree-item">
+    <div class="tree-header directory" onclick="toggleTree(this)">
+        <div class="tree-title">
+            <span class="tree-icon">{{ icons.icon('folder', 16) }}</span>
+            <span class="tree-name">{{ node.name }}</span>
+            <span class="tree-stats">
+                {% if stats.total_lessons %}{{ stats.completed_lessons }}/{{ stats.total_lessons }} watched{% else %}Empty{% endif %}
+            </span>
+        </div>
+        {% if node.children or node.lessons %}
+        <button class="tree-toggle">▶</button>
+        {% endif %}
+    </div>
+
+    {% if node.children or node.lessons %}
+    <div class="tree-content">
+        {% for child_name, child_node in node.children.items() %}
+            {{ render_tree_node(child_node, course_path, current_lesson, depth + 1) }}
+        {% endfor %}
+
+        {% for lesson in node.lessons %}
+        {% set lesson_relative_path = lesson.path|replace('\\', '/')|replace(course_path|replace('\\', '/'), '')|replace('//', '/')|replace('/', '', 1) %}
+        {% set percent_watched = 100 if lesson.completed else (((100 * lesson.progress_seconds / lesson.duration_seconds)|round|int) if (lesson.duration_seconds and lesson.progress_seconds) else 0) %}
+        {% set is_current = current_lesson and lesson.path == current_lesson.path %}
+        <div class="lesson-item {% if is_current %}current{% elif lesson.completed %}completed{% elif percent_watched %}in-progress{% endif %}"
+             {% if not is_current %}onclick="window.location.href='/lesson/{{ lesson_relative_path }}/{{ lesson.title|replace(' ', '_') }}'"{% endif %}>
+            <div class="lesson-title">
+                <span class="lesson-icon">
+                    {% if lesson.lesson_type == 'video' %}{{ icons.icon('video', 16) }}
+                    {% elif lesson.lesson_type == 'audio' %}{{ icons.icon('music', 16) }}
+                    {% elif lesson.lesson_type == 'quiz' %}{{ icons.icon('clipboard', 16) }}
+                    {% elif lesson.lesson_type == 'mixed' %}{{ icons.icon('package', 16) }}
+                    {% else %}{{ icons.icon('file-text', 16) }}{% endif %}
+                </span>
+                <span class="lesson-name">{{ lesson.title }}</span>
+            </div>
+            <div class="lesson-meta">
+                <span class="lesson-type {{ lesson.lesson_type }}">{{ lesson.lesson_type|title }}</span>
+                {% if lesson.duration_seconds and lesson.duration_seconds >= 60 %}
+                <span class="lesson-duration">{{ lesson.duration_seconds|format_duration }}</span>
+                {% endif %}
+                {% if lesson.completed %}
+                <span class="status-icon completed">{{ icons.icon('check', 14) }}</span>
+                {% elif percent_watched %}
+                <span class="watched-badge">{{ percent_watched }}% watched</span>
+                {% else %}
+                <span class="status-icon pending">{{ icons.icon('circle', 14) }}</span>
+                {% endif %}
+            </div>
+            {% if percent_watched %}
+            <div class="lesson-progress-track"><div class="lesson-progress-fill" style="width: {{ percent_watched }}%;"></div></div>
+            {% endif %}
+        </div>
+        {% endfor %}
+    </div>
+    {% endif %}
+</div>
+{% endmacro %}
diff --git a/templates/course_dashboard.html b/templates/course_dashboard.html
index 57feeb3..b44909c 100644
--- a/templates/course_dashboard.html
+++ b/templates/course_dashboard.html
@@ -1,4 +1,5 @@
 {% import '_icons.html' as icons %}
+{% import '_course_tree.html' as tree %}
 <!DOCTYPE html>
 <html lang="en">
 <head>
@@ -1089,67 +1090,7 @@
             </div>
 
             <div class="tree-container">
-                {% macro render_tree_node(node, depth=0) %}
-                {% set stats = section_stats(node) %}
-                <div class="tree-item">
-                    <div class="tree-header directory" onclick="toggleTree(this)">
-                        <div class="tree-title">
-                            <span class="tree-icon">{{ icons.icon('folder', 16) }}</span>
-                            <span class="tree-name">{{ node.name }}</span>
-                            <span class="tree-stats">
-                                {% if stats.total_lessons %}{{ stats.completed_lessons }}/{{ stats.total_lessons }} watched{% else %}Empty{% endif %}
-                            </span>
-                        </div>
-                        {% if node.children or node.lessons %}
-                        <button class="tree-toggle">▶</button>
-                        {% endif %}
-                    </div>
-                    
-                    {% if node.children or node.lessons %}
-                    <div class="tree-content">
-                        {% for child_name, child_node in node.children.items() %}
-                            {{ render_tree_node(child_node, depth + 1) }}
-                        {% endfor %}
-                        
-                        {% for lesson in node.lessons %}
-                        {% set lesson_relative_path = lesson.path|replace('\\', '/')|replace(course.path|replace('\\', '/'), '')|replace('//', '/')|replace('/', '', 1) %}
-                        {% set percent_watched = 100 if lesson.completed else (((100 * lesson.progress_seconds / lesson.duration_seconds)|round|int) if (lesson.duration_seconds and lesson.progress_seconds) else 0) %}
-                        <div class="lesson-item {% if lesson.completed %}completed{% elif percent_watched %}in-progress{% endif %}"
-                             onclick="window.location.href='/lesson/{{ lesson_relative_path }}/{{ lesson.title|replace(' ', '_') }}'">
-                            <div class="lesson-title">
-                                <span class="lesson-icon">
-                                    {% if lesson.lesson_type == 'video' %}{{ icons.icon('video', 16) }}
-                                    {% elif lesson.lesson_type == 'audio' %}{{ icons.icon('music', 16) }}
-                                    {% elif lesson.lesson_type == 'quiz' %}{{ icons.icon('clipboard', 16) }}
-                                    {% elif lesson.lesson_type == 'mixed' %}{{ icons.icon('package', 16) }}
-                                    {% else %}{{ icons.icon('file-text', 16) }}{% endif %}
-                                </span>
-                                <span class="lesson-name">{{ lesson.title }}</span>
-                            </div>
-                            <div class="lesson-meta">
-                                <span class="lesson-type {{ lesson.lesson_type }}">{{ lesson.lesson_type|title }}</span>
-                                {% if lesson.duration_seconds and lesson.duration_seconds >= 60 %}
-                                <span class="lesson-duration">{{ lesson.duration_seconds|format_duration }}</span>
-                                {% endif %}
-                                {% if lesson.completed %}
-                                <span class="status-icon completed">{{ icons.icon('check', 14) }}</span>
-                                {% elif percent_watched %}
-                                <span class="watched-badge">{{ percent_watched }}% watched</span>
-                                {% else %}
-                                <span class="status-icon pending">{{ icons.icon('circle', 14) }}</span>
-                                {% endif %}
-                            </div>
-                            {% if percent_watched %}
-                            <div class="lesson-progress-track"><div class="lesson-progress-fill" style="width: {{ percent_watched }}%;"></div></div>
-                            {% endif %}
-                        </div>
-                        {% endfor %}
-                    </div>
-                    {% endif %}
-                </div>
-                {% endmacro %}
-                
-                {{ render_tree_node(course.root_node) }}
+                {{ tree.render_tree_node(course.root_node, course.path) }}
             </div>
         </div>
     {% else %}
diff --git a/templates/lesson_view.html b/templates/lesson_view.html
index f05b5eb..03fd7c2 100644
--- a/templates/lesson_view.html
+++ b/templates/lesson_view.html
@@ -1,4 +1,5 @@
 {% import '_icons.html' as icons %}
+{% import '_course_tree.html' as tree %}
 <!DOCTYPE html>
 <html lang="en">
 <head>
@@ -134,14 +135,229 @@
             vertical-align: -3px;
             flex-shrink: 0;
         }
-        .container { 
-            max-width: var(--container-max-width); 
+        .container {
+            max-width: var(--container-max-width);
             width: 95%;
-            margin: 20px auto; 
+            margin: 20px auto;
             background: var(--bg-secondary);
             padding: 20px;
             border-radius: var(--radius);
         }
+        .lesson-layout {
+            max-width: var(--container-max-width);
+            width: 95%;
+            margin: 20px auto;
+            display: flex;
+            align-items: flex-start;
+            gap: 20px;
+        }
+        .lesson-layout .container {
+            width: auto;
+            max-width: none;
+            margin: 0;
+        }
+        .lesson-main {
+            flex: 1;
+            min-width: 0;
+        }
+        .lesson-sidebar {
+            flex: 0 0 300px;
+            position: sticky;
+            top: 20px;
+            max-height: calc(100vh - 40px);
+            overflow-y: auto;
+        }
+        .lesson-sidebar h3 {
+            margin-top: 0;
+        }
+        @media (max-width: 900px) {
+            .lesson-layout {
+                flex-direction: column;
+            }
+            .lesson-sidebar {
+                flex: 1 1 auto;
+                width: 100%;
+                position: static;
+                max-height: 420px;
+            }
+        }
+        /* Course-outline sidebar tree - scoped under .lesson-sidebar so
+           these don't collide with this page's own .lesson-title (the H1)
+           and similarly-named rules. Mirrors course_dashboard.html's tree
+           styling (shared macro, see _course_tree.html) at a denser size
+           for the narrower column. */
+        .lesson-sidebar .tree-container {
+            margin-top: 10px;
+        }
+        .lesson-sidebar .tree-item {
+            margin-bottom: 5px;
+        }
+        .lesson-sidebar .tree-header {
+            background: var(--bg-tertiary);
+            padding: 10px 12px;
+            border-radius: var(--radius);
+            cursor: pointer;
+            display: flex;
+            align-items: center;
+            justify-content: space-between;
+            transition: background 0.3s;
+            border-left: 3px solid #666;
+        }
+        .lesson-sidebar .tree-header:hover {
+            background: var(--bg-tertiary-hover);
+        }
+        .lesson-sidebar .tree-header.directory {
+            border-left-color: var(--accent);
+        }
+        .lesson-sidebar .tree-title {
+            display: flex;
+            align-items: center;
+            gap: 8px;
+            flex: 1;
+            min-width: 0;
+        }
+        .lesson-sidebar .tree-icon {
+            font-size: 1.1em;
+            width: 18px;
+            text-align: center;
+            flex-shrink: 0;
+        }
+        .lesson-sidebar .tree-name {
+            font-weight: 500;
+            flex: 1;
+            min-width: 0;
+            overflow: hidden;
+            text-overflow: ellipsis;
+            white-space: nowrap;
+            font-size: 0.9em;
+        }
+        .lesson-sidebar .tree-stats {
+            font-size: 0.75em;
+            color: var(--text-muted);
+            margin-left: 8px;
+            flex-shrink: 0;
+            white-space: nowrap;
+        }
+        .lesson-sidebar .tree-toggle {
+            background: none;
+            border: none;
+            color: var(--text-primary);
+            font-size: 1.1em;
+            cursor: pointer;
+            padding: 4px;
+            border-radius: 3px;
+            transition: background 0.3s;
+        }
+        .lesson-sidebar .tree-toggle:hover {
+            background: #555;
+        }
+        .lesson-sidebar .tree-content {
+            margin-left: 16px;
+            margin-top: 5px;
+            display: none;
+        }
+        .lesson-sidebar .tree-content.expanded {
+            display: block;
+        }
+        .lesson-sidebar .lesson-item {
+            background: var(--bg-tertiary);
+            padding: 8px 12px;
+            border-radius: var(--radius);
+            margin-bottom: 5px;
+            display: flex;
+            flex-wrap: wrap;
+            justify-content: space-between;
+            align-items: center;
+            transition: all 0.2s;
+            cursor: pointer;
+            border-left: 3px solid #666;
+            position: relative;
+            overflow: hidden;
+            gap: 4px;
+        }
+        .lesson-sidebar .lesson-item:hover {
+            border-left-color: var(--accent);
+            background: var(--bg-tertiary-hover);
+        }
+        .lesson-sidebar .lesson-item.completed {
+            border-left-color: var(--success);
+        }
+        .lesson-sidebar .lesson-item.in-progress {
+            border-left-color: var(--accent);
+        }
+        .lesson-sidebar .lesson-item.current {
+            border-left-color: var(--accent);
+            background: var(--bg-tertiary-hover);
+            cursor: default;
+            font-weight: 600;
+        }
+        .lesson-sidebar .lesson-progress-track {
+            position: absolute;
+            bottom: 0;
+            left: 0;
+            right: 0;
+            height: 3px;
+            background: rgba(255, 255, 255, 0.08);
+        }
+        .lesson-sidebar .lesson-progress-fill {
+            height: 100%;
+            background: var(--accent);
+        }
+        .lesson-sidebar .lesson-item.completed .lesson-progress-fill {
+            background: var(--success);
+        }
+        .lesson-sidebar .watched-badge {
+            font-size: 0.7em;
+            background: var(--bg-primary);
+            color: var(--accent);
+            padding: 1px 6px;
+            border-radius: 3px;
+            border: 1px solid var(--accent);
+            white-space: nowrap;
+        }
+        .lesson-sidebar .lesson-item .lesson-title {
+            display: flex;
+            align-items: center;
+            gap: 6px;
+            flex: 1;
+            min-width: 0;
+        }
+        .lesson-sidebar .lesson-icon {
+            font-size: 1em;
+            flex-shrink: 0;
+        }
+        .lesson-sidebar .lesson-name {
+            font-size: 0.85em;
+            overflow: hidden;
+            text-overflow: ellipsis;
+            white-space: nowrap;
+        }
+        .lesson-sidebar .lesson-meta {
+            font-size: 0.75em;
+            color: var(--text-muted);
+            display: flex;
+            align-items: center;
+            gap: 4px;
+            flex-shrink: 0;
+        }
+        .lesson-sidebar .lesson-type {
+            display: none;
+        }
+        .lesson-sidebar .lesson-duration {
+            font-size: 0.75em;
+            color: var(--text-muted);
+            white-space: nowrap;
+        }
+        .lesson-sidebar .status-icon {
+            font-size: 1.1em;
+            font-weight: bold;
+        }
+        .lesson-sidebar .status-icon.completed {
+            color: var(--success);
+        }
+        .lesson-sidebar .status-icon.pending {
+            color: var(--text-muted);
+        }
         video, audio { 
             width: 100%; 
             max-width: 100%; 
@@ -207,65 +423,6 @@
         .outline-section {
             margin: 20px 0;
         }
-        .section-lessons {
-            margin: 20px 0;
-            background: var(--bg-tertiary);
-            border-radius: var(--radius);
-        }
-        .section-lessons-header {
-            display: flex;
-            align-items: center;
-            gap: 8px;
-            padding: 10px 14px;
-            cursor: pointer;
-            font-weight: 600;
-        }
-        .section-lessons-count {
-            color: var(--text-muted);
-            font-weight: 400;
-            font-size: 0.85em;
-        }
-        .section-lessons-list {
-            max-height: 0;
-            overflow: hidden;
-            transition: max-height 0.25s ease;
-        }
-        .section-lessons-list.expanded {
-            max-height: 2000px;
-        }
-        .section-lesson-row {
-            display: flex;
-            align-items: center;
-            gap: 10px;
-            padding: 8px 14px;
-            border-top: 1px solid var(--border-color);
-            text-decoration: none;
-            color: var(--text-primary);
-            transition: background 0.2s;
-        }
-        a.section-lesson-row:hover {
-            background: var(--bg-tertiary-hover);
-        }
-        .section-lesson-row.current {
-            background: var(--bg-tertiary-hover);
-            font-weight: 600;
-            cursor: default;
-        }
-        .section-lesson-title {
-            flex: 1;
-            min-width: 0;
-            overflow: hidden;
-            text-overflow: ellipsis;
-            white-space: nowrap;
-        }
-        .section-lesson-status {
-            font-size: 0.8em;
-            color: var(--text-muted);
-            flex-shrink: 0;
-        }
-        .section-lesson-status.completed {
-            color: var(--success);
-        }
         .note-status {
             display: block;
             font-size: 0.85em;
@@ -525,7 +682,8 @@
     </div>
 
     <div class="page-content">
-    <div class="container">
+    <div class="lesson-layout">
+    <div class="container lesson-main">
         <h1 class="lesson-title">{{ lesson.title }}</h1>
         
         <div class="lesson-path">
@@ -590,43 +748,6 @@
             {% endif %}
         </div>
 
-        {% if section_lessons and section_lessons|length > 1 %}
-        <div class="section-lessons">
-            <div class="section-lessons-header" onclick="toggleSectionLessons()">
-                <span id="section-lessons-arrow">▾</span>
-                <span>Lessons in this section</span>
-                <span class="section-lessons-count">({{ section_lessons|length }})</span>
-            </div>
-            <div class="section-lessons-list expanded" id="section-lessons-list-wrap">
-                {% for item in section_lessons %}
-                {% if item.is_current %}
-                <span class="section-lesson-row current">
-                {% else %}
-                <a class="section-lesson-row" href="/lesson/{{ item.url }}">
-                {% endif %}
-                    <span class="section-lesson-icon">
-                        {% if item.lesson_type == 'video' %}{{ icons.icon('video', 16) }}
-                        {% elif item.lesson_type == 'audio' %}{{ icons.icon('music', 16) }}
-                        {% elif item.lesson_type == 'quiz' %}{{ icons.icon('clipboard', 16) }}
-                        {% elif item.lesson_type == 'mixed' %}{{ icons.icon('package', 16) }}
-                        {% else %}{{ icons.icon('file-text', 16) }}{% endif %}
-                    </span>
-                    <span class="section-lesson-title">{{ item.title }}</span>
-                    {% if item.completed %}
-                    <span class="section-lesson-status completed">{{ icons.icon('check', 14) }}</span>
-                    {% elif item.percent_watched %}
-                    <span class="section-lesson-status">{{ item.percent_watched }}%</span>
-                    {% endif %}
-                {% if item.is_current %}
-                </span>
-                {% else %}
-                </a>
-                {% endif %}
-                {% endfor %}
-            </div>
-        </div>
-        {% endif %}
-
         <div class="outline-section">
             <h3>Push to Outline</h3>
             <div class="outline-topic-row">
@@ -673,6 +794,15 @@
             <button disabled>Next →</button>
             {% endif %}
         </div>
+    </div>
+
+    <div class="container lesson-sidebar">
+        <h3>Course Outline</h3>
+        <div class="tree-container">
+            {{ tree.render_tree_node(course.root_node, course.path, lesson) }}
+        </div>
+    </div>
+    </div>
 
         <script>
             // Client-rendered mirror of a few templates/_icons.html entries -
@@ -1055,33 +1185,41 @@
                 if (notesPanelToggleArrow) notesPanelToggleArrow.textContent = '▴';
             }
 
-            // "Lessons in this section" defaults open (unlike notes, this
-            // is primary navigation) - only collapse it if the user
-            // explicitly did so on a previous visit.
-            function toggleSectionLessons() {
-                const listWrap = document.getElementById('section-lessons-list-wrap');
-                const arrow = document.getElementById('section-lessons-arrow');
-                if (!listWrap) return;
-                const expanded = listWrap.classList.toggle('expanded');
-                if (arrow) arrow.textContent = expanded ? '▾' : '▸';
-                localStorage.setItem('offlineu-section-lessons-expanded', expanded ? '1' : '0');
-            }
-
-            (function() {
-                const listWrap = document.getElementById('section-lessons-list-wrap');
-                const arrow = document.getElementById('section-lessons-arrow');
-                if (listWrap && localStorage.getItem('offlineu-section-lessons-expanded') === '0') {
-                    listWrap.classList.remove('expanded');
-                    if (arrow) arrow.textContent = '▸';
-                }
-            })();
-
             function openQuickCapture() {
                 if (activeMedia && !activeMedia.paused) activeMedia.pause();
                 updateQuickCaptureBadge();
                 if (quickNoteInput) quickNoteInput.focus();
             }
 
+            // ---- Course outline sidebar (shared tree markup/macro with the
+            // dashboard's loaded-course view - see _course_tree.html) ----
+            function toggleTree(element) {
+                const content = element.nextElementSibling;
+                const toggleBtn = element.querySelector('.tree-toggle');
+                if (content && content.classList.contains('tree-content')) {
+                    const isExpanded = content.classList.toggle('expanded');
+                    if (toggleBtn) toggleBtn.textContent = isExpanded ? '▼' : '▶';
+                }
+            }
+
+            // Sections default collapsed (same as the dashboard) - expand
+            // just the ancestor chain down to the current lesson so it's
+            // visible without the user having to hunt for it, and scroll
+            // it into view within the sidebar's own scroll area.
+            (function revealCurrentLessonInSidebar() {
+                const current = document.querySelector('.lesson-sidebar .lesson-item.current');
+                if (!current) return;
+                let content = current.closest('.tree-content');
+                while (content) {
+                    content.classList.add('expanded');
+                    const header = content.previousElementSibling;
+                    const toggleBtn = header ? header.querySelector('.tree-toggle') : null;
+                    if (toggleBtn) toggleBtn.textContent = '▼';
+                    content = content.parentElement ? content.parentElement.closest('.tree-content') : null;
+                }
+                current.scrollIntoView({ block: 'center' });
+            })();
+
             renderNotes();
 
             // Seek once metadata is available (activeMedia.duration is NaN
@@ -1442,7 +1580,6 @@
             }
         </script>
     </div>
-    </div>
 
     <footer class="app-footer">
         <div class="container-inner">