feat: implement group EPUB upload and section splitting (US #29)

Backend:
- Create hermes Django app with models: ReadingGroup, GroupBook, Section, ReadingSchedule, MemberProgress
- EPUB section splitting service with automatic detection and reading time estimation
- Section recommendation engine for 4-week meeting schedule
- REST API endpoints for groups, books, sections, schedule, and member progress
- Manual section adjustment (merge/split) support

Frontend:
- GroupsPage: list/create reading groups
- GroupDetailPage: manage members, upload EPUB to group, view group books
- GroupBookPage: section breakdown with merge/split controls, reading schedule, member progress
- API client and TypeScript types for all group operations
- i18n keys for English and Spanish

Shared:
- Group-related types and API endpoint constants in packages/shared

backend/apps/groups/admin.py

@@ -0,0 +1,46 @@
+from django.contrib import admin
+
+from apps.groups.models import (
+    GroupBook,
+    MemberProgress,
+    ReadingGroup,
+    ReadingGroupMembership,
+    ReadingSchedule,
+    Section,
+)
+
+
+@admin.register(ReadingGroup)
+class ReadingGroupAdmin(admin.ModelAdmin):
+    list_display = ["name", "admin", "created_at"]
+    search_fields = ["name", "admin__email"]
+
+
+@admin.register(ReadingGroupMembership)
+class ReadingGroupMembershipAdmin(admin.ModelAdmin):
+    list_display = ["user", "group", "role", "joined_at"]
+    list_filter = ["role", "group"]
+
+
+@admin.register(GroupBook)
+class GroupBookAdmin(admin.ModelAdmin):
+    list_display = ["title", "group", "status", "uploaded_by", "created_at"]
+    list_filter = ["status"]
+    search_fields = ["title", "group__name"]
+
+
+@admin.register(Section)
+class SectionAdmin(admin.ModelAdmin):
+    list_display = ["title", "group_book", "order", "estimated_reading_minutes"]
+    ordering = ["group_book", "order"]
+
+
+@admin.register(ReadingSchedule)
+class ReadingScheduleAdmin(admin.ModelAdmin):
+    list_display = ["group_book", "meeting_number", "week_date"]
+    ordering = ["group_book", "meeting_number"]
+
+
+@admin.register(MemberProgress)
+class MemberProgressAdmin(admin.ModelAdmin):
+    list_display = ["user", "group_book", "current_section", "updated_at"]

backend/apps/groups/apps.py

@@ -0,0 +1,7 @@
+from django.apps import AppConfig
+
+
+class GroupsConfig(AppConfig):
+    default_auto_field = "django.db.models.BigAutoField"
+    name = "apps.groups"
+    verbose_name = "Reading Groups"

backend/apps/groups/migrations/0001_initial.py

@@ -0,0 +1,154 @@
+# Generated by Django 5.1.7 on 2026-06-20 19:21
+
+import django.db.models.deletion
+from django.conf import settings
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = [
+        ('books', '0003_readingprogress_epub_location'),
+        migrations.swappable_dependency(settings.AUTH_USER_MODEL),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='ReadingGroup',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(db_index=True, max_length=256)),
+                ('description', models.TextField(blank=True, default='')),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+                ('admin', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='administered_groups', to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                'verbose_name': 'Reading Group',
+                'verbose_name_plural': 'Reading Groups',
+                'db_table': 'groups_reading_group',
+                'ordering': ['-created_at'],
+            },
+        ),
+        migrations.CreateModel(
+            name='GroupBook',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('title', models.CharField(db_index=True, max_length=512)),
+                ('status', models.CharField(choices=[('active', 'Active'), ('replaced', 'Replaced')], db_index=True, default='active', max_length=16)),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+                ('ebook', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='group_books', to='books.ebook')),
+                ('uploaded_by', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='uploaded_group_books', to=settings.AUTH_USER_MODEL)),
+                ('group', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='group_books', to='groups.readinggroup')),
+            ],
+            options={
+                'verbose_name': 'Group Book',
+                'verbose_name_plural': 'Group Books',
+                'db_table': 'groups_group_book',
+                'ordering': ['-created_at'],
+            },
+        ),
+        migrations.CreateModel(
+            name='ReadingGroupMembership',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('role', models.CharField(choices=[('admin', 'Admin'), ('member', 'Member')], default='member', max_length=16)),
+                ('joined_at', models.DateTimeField(auto_now_add=True)),
+                ('group', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='memberships', to='groups.readinggroup')),
+                ('user', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to=settings.AUTH_USER_MODEL)),
+            ],
+            options={
+                'verbose_name': 'Reading Group Membership',
+                'verbose_name_plural': 'Reading Group Memberships',
+                'db_table': 'groups_membership',
+            },
+        ),
+        migrations.AddField(
+            model_name='readinggroup',
+            name='members',
+            field=models.ManyToManyField(related_name='reading_groups', through='groups.ReadingGroupMembership', to=settings.AUTH_USER_MODEL),
+        ),
+        migrations.CreateModel(
+            name='ReadingSchedule',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('meeting_number', models.PositiveIntegerField()),
+                ('week_date', models.DateField()),
+                ('section_ids', models.JSONField(default=list, help_text='Ordered list of Section IDs for this meeting')),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('group_book', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='schedules', to='groups.groupbook')),
+            ],
+            options={
+                'verbose_name': 'Reading Schedule',
+                'verbose_name_plural': 'Reading Schedules',
+                'db_table': 'groups_reading_schedule',
+                'ordering': ['meeting_number'],
+            },
+        ),
+        migrations.CreateModel(
+            name='Section',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('title', models.CharField(max_length=512)),
+                ('order', models.PositiveIntegerField(db_index=True)),
+                ('start_chapter_index', models.PositiveIntegerField(default=0)),
+                ('end_chapter_index', models.PositiveIntegerField(default=0)),
+                ('estimated_reading_minutes', models.PositiveIntegerField(default=0)),
+                ('created_at', models.DateTimeField(auto_now_add=True)),
+                ('group_book', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='sections', to='groups.groupbook')),
+            ],
+            options={
+                'verbose_name': 'Section',
+                'verbose_name_plural': 'Sections',
+                'db_table': 'groups_section',
+                'ordering': ['order'],
+            },
+        ),
+        migrations.CreateModel(
+            name='MemberProgress',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('completed_sections', models.JSONField(default=list, help_text='Ordered list of completed Section IDs')),
+                ('updated_at', models.DateTimeField(auto_now=True)),
+                ('group_book', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='member_progress', to='groups.groupbook')),
+                ('user', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='group_progress', to=settings.AUTH_USER_MODEL)),
+                ('current_section', models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='current_readers', to='groups.section')),
+            ],
+            options={
+                'verbose_name': 'Member Progress',
+                'verbose_name_plural': 'Member Progress',
+                'db_table': 'groups_member_progress',
+            },
+        ),
+        migrations.AddIndex(
+            model_name='groupbook',
+            index=models.Index(fields=['group', 'status'], name='groups_grou_group_i_afdbf7_idx'),
+        ),
+        migrations.AlterUniqueTogether(
+            name='readinggroupmembership',
+            unique_together={('user', 'group')},
+        ),
+        migrations.AddIndex(
+            model_name='readingschedule',
+            index=models.Index(fields=['group_book', 'meeting_number'], name='groups_read_group_b_2fc416_idx'),
+        ),
+        migrations.AlterUniqueTogether(
+            name='readingschedule',
+            unique_together={('group_book', 'meeting_number')},
+        ),
+        migrations.AddIndex(
+            model_name='section',
+            index=models.Index(fields=['group_book', 'order'], name='groups_sect_group_b_e2810a_idx'),
+        ),
+        migrations.AlterUniqueTogether(
+            name='section',
+            unique_together={('group_book', 'order')},
+        ),
+        migrations.AlterUniqueTogether(
+            name='memberprogress',
+            unique_together={('user', 'group_book')},
+        ),
+    ]

backend/apps/groups/models.py

@@ -0,0 +1,161 @@
+from django.conf import settings
+from django.db import models
+
+from apps.books.models import EBook
+
+
+class ReadingGroup(models.Model):
+    """A reading group with an admin and members."""
+
+    name = models.CharField(max_length=256, db_index=True)
+    description = models.TextField(blank=True, default="")
+    admin = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="administered_groups",
+    )
+    members = models.ManyToManyField(
+        settings.AUTH_USER_MODEL,
+        through="ReadingGroupMembership",
+        related_name="reading_groups",
+    )
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "groups_reading_group"
+        verbose_name = "Reading Group"
+        verbose_name_plural = "Reading Groups"
+        ordering = ["-created_at"]
+
+    def __str__(self) -> str:
+        return self.name
+
+
+class ReadingGroupMembership(models.Model):
+    class Role(models.TextChoices):
+        ADMIN = "admin", "Admin"
+        MEMBER = "member", "Member"
+
+    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
+    group = models.ForeignKey(ReadingGroup, on_delete=models.CASCADE, related_name="memberships")
+    role = models.CharField(max_length=16, choices=Role.choices, default=Role.MEMBER)
+    joined_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        db_table = "groups_membership"
+        unique_together = [("user", "group")]
+        verbose_name = "Reading Group Membership"
+        verbose_name_plural = "Reading Group Memberships"
+
+    def __str__(self) -> str:
+        return f"{self.user} in {self.group.name} ({self.role})"
+
+
+class GroupBook(models.Model):
+    """Links an uploaded EBook to a reading group."""
+
+    class Status(models.TextChoices):
+        ACTIVE = "active", "Active"
+        REPLACED = "replaced", "Replaced"
+
+    group = models.ForeignKey(
+        ReadingGroup, on_delete=models.CASCADE, related_name="group_books"
+    )
+    ebook = models.ForeignKey(
+        EBook, on_delete=models.CASCADE, related_name="group_books"
+    )
+    uploaded_by = models.ForeignKey(
+        settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="uploaded_group_books"
+    )
+    title = models.CharField(max_length=512, db_index=True)
+    status = models.CharField(
+        max_length=16, choices=Status.choices, default=Status.ACTIVE, db_index=True
+    )
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "groups_group_book"
+        verbose_name = "Group Book"
+        verbose_name_plural = "Group Books"
+        ordering = ["-created_at"]
+        indexes = [models.Index(fields=["group", "status"])]
+
+    def __str__(self) -> str:
+        return f"{self.group.name} — {self.title}"
+
+
+class Section(models.Model):
+    """A section/chunk of a GroupBook for group reading."""
+
+    group_book = models.ForeignKey(
+        GroupBook, on_delete=models.CASCADE, related_name="sections"
+    )
+    title = models.CharField(max_length=512)
+    order = models.PositiveIntegerField(db_index=True)
+    start_chapter_index = models.PositiveIntegerField(default=0)
+    end_chapter_index = models.PositiveIntegerField(default=0)
+    estimated_reading_minutes = models.PositiveIntegerField(default=0)
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        db_table = "groups_section"
+        verbose_name = "Section"
+        verbose_name_plural = "Sections"
+        ordering = ["order"]
+        unique_together = [("group_book", "order")]
+        indexes = [models.Index(fields=["group_book", "order"])]
+
+    def __str__(self) -> str:
+        return f"{self.group_book.title} — Section {self.order}: {self.title}"
+
+
+class ReadingSchedule(models.Model):
+    """Reading schedule mapping sections to weekly meetings."""
+
+    group_book = models.ForeignKey(
+        GroupBook, on_delete=models.CASCADE, related_name="schedules"
+    )
+    meeting_number = models.PositiveIntegerField()
+    week_date = models.DateField()
+    section_ids = models.JSONField(default=list, help_text="Ordered list of Section IDs for this meeting")
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        db_table = "groups_reading_schedule"
+        verbose_name = "Reading Schedule"
+        verbose_name_plural = "Reading Schedules"
+        ordering = ["meeting_number"]
+        unique_together = [("group_book", "meeting_number")]
+        indexes = [models.Index(fields=["group_book", "meeting_number"])]
+
+    def __str__(self) -> str:
+        return f"{self.group_book.title} — Meeting {self.meeting_number}"
+
+
+class MemberProgress(models.Model):
+    """Tracks a member's progress through sections of a group book."""
+
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="group_progress"
+    )
+    group_book = models.ForeignKey(
+        GroupBook, on_delete=models.CASCADE, related_name="member_progress"
+    )
+    current_section = models.ForeignKey(
+        Section, on_delete=models.SET_NULL, null=True, blank=True, related_name="current_readers"
+    )
+    completed_sections = models.JSONField(
+        default=list, help_text="Ordered list of completed Section IDs"
+    )
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "groups_member_progress"
+        verbose_name = "Member Progress"
+        verbose_name_plural = "Member Progress"
+        unique_together = [("user", "group_book")]
+
+    def __str__(self) -> str:
+        return f"{self.user} — {self.group_book.title}"

backend/apps/groups/serializers.py

@@ -0,0 +1,185 @@
+from __future__ import annotations
+
+from rest_framework import serializers
+
+from apps.groups.models import (
+    GroupBook,
+    MemberProgress,
+    ReadingGroup,
+    ReadingGroupMembership,
+    ReadingSchedule,
+    Section,
+)
+from apps.books.serializers import EBookListSerializer
+
+
+class ReadingGroupMembershipSerializer(serializers.ModelSerializer):
+    user_email = serializers.CharField(source="user.email", read_only=True)
+    user_username = serializers.CharField(source="user.username", read_only=True)
+
+    class Meta:
+        model = ReadingGroupMembership
+        fields = [
+            "id", "user", "user_email", "user_username",
+            "role", "joined_at",
+        ]
+        read_only_fields = ["id", "joined_at"]
+
+
+class ReadingGroupListSerializer(serializers.ModelSerializer):
+    member_count = serializers.SerializerMethodField()
+    admin_email = serializers.CharField(source="admin.email", read_only=True)
+
+    class Meta:
+        model = ReadingGroup
+        fields = [
+            "id", "name", "description", "admin", "admin_email",
+            "member_count", "created_at", "updated_at",
+        ]
+
+    def get_member_count(self, obj: ReadingGroup) -> int:
+        return obj.memberships.count()
+
+
+class ReadingGroupDetailSerializer(serializers.ModelSerializer):
+    admin_email = serializers.CharField(source="admin.email", read_only=True)
+    members = ReadingGroupMembershipSerializer(source="memberships", many=True, read_only=True)
+
+    class Meta:
+        model = ReadingGroup
+        fields = [
+            "id", "name", "description", "admin", "admin_email",
+            "members", "created_at", "updated_at",
+        ]
+
+
+class ReadingGroupCreateSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = ReadingGroup
+        fields = ["name", "description"]
+
+
+class AddMemberSerializer(serializers.Serializer):
+    user_id = serializers.IntegerField()
+
+    def validate_user_id(self, value: int) -> int:
+        from django.conf import settings
+        User = settings.AUTH_USER_MODEL
+        if not User.objects.filter(id=value).exists():
+            raise serializers.ValidationError("User not found.")
+        return value
+
+
+class SectionSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = Section
+        fields = [
+            "id", "title", "order", "start_chapter_index",
+            "end_chapter_index", "estimated_reading_minutes", "created_at",
+        ]
+        read_only_fields = ["id", "created_at"]
+
+
+class SectionAdjustSerializer(serializers.Serializer):
+    """Payload for manual section adjustments (merge/split)."""
+    operation = serializers.ChoiceField(choices=["merge", "split"])
+    section_ids = serializers.ListField(
+        child=serializers.IntegerField(), min_length=1,
+        help_text="For merge: list of section IDs to merge. For split: [section_id] to split."
+    )
+    split_at = serializers.IntegerField(
+        required=False, default=2, min_value=2,
+        help_text="Number of new sections when splitting"
+    )
+
+
+class ReadingScheduleSerializer(serializers.ModelSerializer):
+    section_details = serializers.SerializerMethodField()
+
+    class Meta:
+        model = ReadingSchedule
+        fields = [
+            "id", "meeting_number", "week_date", "section_ids",
+            "section_details", "created_at",
+        ]
+        read_only_fields = ["id", "created_at"]
+
+    def get_section_details(self, obj: ReadingSchedule) -> list[dict]:
+        sections = Section.objects.filter(
+            id__in=obj.section_ids, group_book=obj.group_book
+        ).order_by("order")
+        return SectionSerializer(sections, many=True).data
+
+
+class MemberProgressSerializer(serializers.ModelSerializer):
+    user_email = serializers.CharField(source="user.email", read_only=True)
+    user_username = serializers.CharField(source="user.username", read_only=True)
+    current_section_title = serializers.SerializerMethodField()
+
+    class Meta:
+        model = MemberProgress
+        fields = [
+            "id", "user", "user_email", "user_username",
+            "current_section", "current_section_title",
+            "completed_sections", "updated_at",
+        ]
+        read_only_fields = ["id", "updated_at"]
+
+    def get_current_section_title(self, obj: MemberProgress) -> str | None:
+        if obj.current_section:
+            return obj.current_section.title
+        return None
+
+
+class GroupBookListSerializer(serializers.ModelSerializer):
+    ebook = EBookListSerializer(read_only=True)
+    uploaded_by_email = serializers.CharField(source="uploaded_by.email", read_only=True)
+    section_count = serializers.SerializerMethodField()
+
+    class Meta:
+        model = GroupBook
+        fields = [
+            "id", "title", "status", "ebook", "uploaded_by",
+            "uploaded_by_email", "section_count", "created_at", "updated_at",
+        ]
+
+    def get_section_count(self, obj: GroupBook) -> int:
+        return obj.sections.count()
+
+
+class GroupBookDetailSerializer(serializers.ModelSerializer):
+    ebook = EBookListSerializer(read_only=True)
+    uploaded_by_email = serializers.CharField(source="uploaded_by.email", read_only=True)
+    sections = SectionSerializer(many=True, read_only=True)
+    schedules = ReadingScheduleSerializer(source="schedules", many=True, read_only=True)
+
+    class Meta:
+        model = GroupBook
+        fields = [
+            "id", "group", "title", "status", "ebook",
+            "uploaded_by", "uploaded_by_email",
+            "sections", "schedules", "created_at", "updated_at",
+        ]
+
+
+class GroupBookCreateSerializer(serializers.Serializer):
+    ebook_id = serializers.IntegerField()
+    title = serializers.CharField(max_length=512, required=False)
+
+    def validate_ebook_id(self, value: int) -> int:
+        from apps.books.models import EBook
+        if not EBook.objects.filter(id=value).exists():
+            raise serializers.ValidationError("EBook not found.")
+        # Check format is EPUB
+        ebook = EBook.objects.get(id=value)
+        if ebook.format != "epub":
+            raise serializers.ValidationError("Only EPUB format is supported for group books.")
+        return value
+
+    def validate(self, data: dict) -> dict:
+        request = self.context.get("request")
+        if request and not data.get("title"):
+            from apps.books.models import EBook
+            ebook = EBook.objects.get(id=data["ebook_id"])
+            data["title"] = ebook.title
+        return data

backend/apps/groups/services/section_splitting.py

@@ -0,0 +1,241 @@
+"""Automatic section detection and meeting recommendation for group books."""
+
+from __future__ import annotations
+
+import logging
+from datetime import date, timedelta
+from typing import Any
+
+from django.db.models import QuerySet
+
+from apps.books.models import BookChapter, EBook
+from apps.groups.models import GroupBook, ReadingSchedule, Section
+
+logger = logging.getLogger(__name__)
+
+WORDS_PER_MINUTE = 250  # Average reading speed
+
+
+def _fetch_chapter_text(ebook: EBook, chapter: BookChapter) -> str:
+    """Extract plain text from a chapter for word counting."""
+    try:
+        from ebooklib import epub
+        from bs4 import BeautifulSoup
+    except ImportError:
+        return ""
+
+    try:
+        book = epub.read_epub(ebook.file.path)
+        href = chapter.href or ""
+        for item in book.get_items():
+            item_name = item.get_name() or ""
+            if href and (item_name.endswith(href) or href.endswith(item_name)):
+                content = item.get_content()
+                soup = BeautifulSoup(content, "html.parser")
+                body = soup.find("body")
+                if body:
+                    return body.get_text(separator=" ", strip=True)
+                return soup.get_text(separator=" ", strip=True)
+        return ""
+    except Exception:
+        logger.exception("Failed to extract text for chapter %s", chapter.id)
+        return ""
+
+
+def _estimate_reading_minutes(text: str) -> int:
+    """Estimate reading time based on word count at WORDS_PER_MINUTE."""
+    word_count = len(text.split())
+    if word_count == 0:
+        return 1
+    return max(1, round(word_count / WORDS_PER_MINUTE))
+
+
+def detect_sections(group_book: GroupBook) -> list[dict[str, Any]]:
+    """Auto-detect sections from a GroupBook's chapters.
+
+    Groups consecutive chapters into logical sections based on TOC structure.
+    Top-level TOC entries become sections; if there are very few (< 3),
+    groups of ~5 chapters become sections instead.
+    """
+    ebook = group_book.ebook
+    chapters = list(
+        BookChapter.objects.filter(ebook=ebook).order_by("index").select_related("ebook")
+    )
+
+    if not chapters:
+        return []
+
+    top_level = [ch for ch in chapters if not ch.children or len(ch.children) == 0]
+    has_children = [ch for ch in chapters if ch.children and len(ch.children) > 0]
+
+    sections: list[dict[str, Any]] = []
+
+    if len(has_children) >= 3:
+        # Use TOC structure: each top-level chapter (with children) is a section
+        for idx, ch in enumerate(has_children):
+            # Find all child chapters belonging to this parent
+            child_indices = _collect_child_indices(chapters, ch, idx)
+            start_idx = ch.index
+            end_idx = child_indices[-1] if child_indices else start_idx
+
+            section_chapters = [c for c in chapters if start_idx <= c.index <= end_idx]
+            total_text = ""
+            for sc in section_chapters:
+                total_text += " " + _fetch_chapter_text(ebook, sc)
+
+            sections.append({
+                "title": ch.title,
+                "order": idx + 1,
+                "start_chapter_index": start_idx,
+                "end_chapter_index": end_idx + 1,
+                "estimated_reading_minutes": _estimate_reading_minutes(total_text),
+            })
+    else:
+        # Group chapters into chunks of ~5
+        chunk_size = max(1, len(top_level) // 6 if len(top_level) > 6 else 5)
+        chunk_size = max(3, min(chunk_size, 10))
+
+        group_start = 0
+        section_order = 1
+        total = len(top_level) or len(chapters)
+        source = top_level or chapters
+
+        while group_start < total:
+            group_end = min(group_start + chunk_size, total)
+            chunk = source[group_start:group_end]
+
+            total_text = ""
+            for ch in chunk:
+                total_text += " " + _fetch_chapter_text(ebook, ch)
+
+            first_title = chunk[0].title if chunk else "Section"
+            last_title = chunk[-1].title if len(chunk) > 1 else ""
+            title = f"{first_title}" if not last_title or first_title == last_title else f"{first_title} — {last_title}"
+
+            sections.append({
+                "title": title,
+                "order": section_order,
+                "start_chapter_index": chunk[0].index,
+                "end_chapter_index": chunk[-1].index + 1,
+                "estimated_reading_minutes": _estimate_reading_minutes(total_text),
+            })
+            group_start = group_end
+            section_order += 1
+
+    return sections
+
+
+def _collect_child_indices(chapters: list[BookChapter], parent: BookChapter, parent_idx: int) -> list[int]:
+    """Collect indices of all chapters that are children of the given parent TOC entry."""
+    indices: list[int] = [parent.index]
+    child_hrefs: set[str] = set()
+    for child in parent.children:
+        if isinstance(child, dict):
+            child_hrefs.add(child.get("href", ""))
+        elif hasattr(child, "href"):
+            child_hrefs.add(getattr(child, "href", ""))
+
+    for ch in chapters:
+        if ch.index == parent.index:
+            continue
+        if ch.href in child_hrefs or any(
+            ch.href.endswith(h) or h.endswith(ch.href) for h in child_hrefs
+        ):
+            indices.append(ch.index)
+
+    # Also include chapters between this parent and the next parent
+    if parent_idx + 1 < len(chapters):
+        next_parent = chapters[parent_idx + 1]
+        for ch in chapters:
+            if parent.index < ch.index < next_parent.index:
+                indices.append(ch.index)
+
+    return sorted(set(indices))
+
+
+def apply_sections(group_book: GroupBook) -> list[Section]:
+    """Detect sections and persist them to the database, replacing existing ones."""
+    Section.objects.filter(group_book=group_book).delete()
+    sections_data = detect_sections(group_book)
+    created: list[Section] = []
+    for data in sections_data:
+        section = Section.objects.create(
+            group_book=group_book,
+            title=data["title"],
+            order=data["order"],
+            start_chapter_index=data["start_chapter_index"],
+            end_chapter_index=data["end_chapter_index"],
+            estimated_reading_minutes=data["estimated_reading_minutes"],
+        )
+        created.append(section)
+    return created
+
+
+def recommend_meetings(group_book: GroupBook, num_meetings: int = 4) -> list[dict[str, Any]]:
+    """Recommend which sections to assign to each weekly meeting.
+
+    Distributes sections across meetings, trying to balance total reading time.
+    Returns a list of meeting assignments ready for schedule creation.
+    """
+    sections = list(
+        Section.objects.filter(group_book=group_book).order_by("order")
+    )
+
+    if not sections:
+        return []
+
+    # Calculate total minutes to distribute
+    total_minutes = sum(s.estimated_reading_minutes for s in sections)
+    target_per_meeting = total_minutes / num_meetings
+
+    meetings: list[dict[str, Any]] = []
+    current_meeting: list[int] = []
+    current_minutes = 0
+
+    for section in sections:
+        if current_meeting and current_minutes + section.estimated_reading_minutes > target_per_meeting * 1.4:
+            # Start new meeting if adding this section would overshoot too much
+            if len(meetings) < num_meetings - 1:
+                meetings.append({
+                    "meeting_number": len(meetings) + 1,
+                    "section_ids": current_meeting,
+                    "total_minutes": current_minutes,
+                })
+                current_meeting = []
+                current_minutes = 0
+
+        current_meeting.append(section.id)
+        current_minutes += section.estimated_reading_minutes
+
+    # Add the last meeting
+    if current_meeting:
+        meetings.append({
+            "meeting_number": len(meetings) + 1,
+            "section_ids": current_meeting,
+            "total_minutes": current_minutes,
+        })
+
+    # If we have fewer than num_meetings, we could split the largest one
+    # For now, just return what we have
+    return meetings
+
+
+def apply_schedule(group_book: GroupBook, num_meetings: int = 4) -> list[ReadingSchedule]:
+    """Generate and persist a reading schedule."""
+    ReadingSchedule.objects.filter(group_book=group_book).delete()
+
+    recommendations = recommend_meetings(group_book, num_meetings)
+    today = date.today()
+
+    created: list[ReadingSchedule] = []
+    for rec in recommendations:
+        week_date = today + timedelta(weeks=rec["meeting_number"] - 1)
+        schedule = ReadingSchedule.objects.create(
+            group_book=group_book,
+            meeting_number=rec["meeting_number"],
+            week_date=week_date,
+            section_ids=rec["section_ids"],
+        )
+        created.append(schedule)
+
+    return created

backend/apps/groups/urls.py

@@ -0,0 +1,43 @@
+from django.urls import include, path
+from rest_framework.routers import DefaultRouter
+
+from apps.groups.views import GroupBookViewSet, ReadingGroupViewSet
+
+# ReadingGroup routes (standard ViewSet)
+router = DefaultRouter()
+router.register(r"", ReadingGroupViewSet, basename="group")
+
+urlpatterns = [
+    path("", include(router.urls)),
+    # Nested GroupBook routes under a group
+    path(
+        "<int:group_pk>/books/",
+        GroupBookViewSet.as_view({"get": "list", "post": "create"}),
+        name="group-book-list",
+    ),
+    path(
+        "<int:group_pk>/books/<int:pk>/",
+        GroupBookViewSet.as_view({"get": "retrieve", "delete": "destroy"}),
+        name="group-book-detail",
+    ),
+    path(
+        "<int:group_pk>/books/<int:pk>/detect-sections/",
+        GroupBookViewSet.as_view({"post": "detect_sections_action"}),
+        name="group-book-detect-sections",
+    ),
+    path(
+        "<int:group_pk>/books/<int:pk>/adjust-sections/",
+        GroupBookViewSet.as_view({"post": "adjust_sections"}),
+        name="group-book-adjust-sections",
+    ),
+    path(
+        "<int:group_pk>/books/<int:pk>/schedule/",
+        GroupBookViewSet.as_view({"get": "schedule", "post": "schedule", "delete": "schedule"}),
+        name="group-book-schedule",
+    ),
+    path(
+        "<int:group_pk>/books/<int:pk>/progress/",
+        GroupBookViewSet.as_view({"get": "progress", "patch": "progress"}),
+        name="group-book-progress",
+    ),
+]

backend/apps/groups/views.py

@@ -0,0 +1,349 @@
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+from django.db.models import QuerySet
+from django.shortcuts import get_object_or_404
+from rest_framework import permissions, status, viewsets
+from rest_framework.decorators import action
+from rest_framework.request import Request
+from rest_framework.response import Response
+
+from apps.books.models import EBook
+from apps.groups.models import (
+    GroupBook,
+    MemberProgress,
+    ReadingGroup,
+    ReadingGroupMembership,
+    ReadingSchedule,
+    Section,
+)
+from apps.groups.serializers import (
+    AddMemberSerializer,
+    GroupBookCreateSerializer,
+    GroupBookDetailSerializer,
+    GroupBookListSerializer,
+    MemberProgressSerializer,
+    ReadingGroupCreateSerializer,
+    ReadingGroupDetailSerializer,
+    ReadingGroupListSerializer,
+    ReadingScheduleSerializer,
+    SectionAdjustSerializer,
+    SectionSerializer,
+)
+from apps.groups.services.section_splitting import (
+    apply_schedule,
+    apply_sections,
+    detect_sections,
+)
+
+logger = logging.getLogger(__name__)
+
+
+class IsGroupAdmin(permissions.BasePermission):
+    """Only the group admin can modify group resources."""
+
+    def has_permission(self, request: Request, view: object) -> bool:
+        if not request.user.is_authenticated:
+            return False
+        if view.action in ("list", "retrieve"):
+            return True
+        group_id = view.kwargs.get("pk") or view.kwargs.get("group_pk")
+        if group_id:
+            return ReadingGroup.objects.filter(id=group_id, admin=request.user).exists()
+        return True
+
+    def has_object_permission(self, request: Request, view: object, obj: ReadingGroup) -> bool:
+        if request.method in permissions.SAFE_METHODS:
+            return True
+        return obj.admin == request.user
+
+
+class IsGroupMember(permissions.BasePermission):
+    """Only group members (including admin) can view group content."""
+
+    def has_permission(self, request: Request, view: object) -> bool:
+        if not request.user.is_authenticated:
+            return False
+        group_id = view.kwargs.get("pk") or view.kwargs.get("group_pk")
+        if group_id:
+            return ReadingGroupMembership.objects.filter(
+                group_id=group_id, user=request.user
+            ).exists()
+        return True
+
+
+class ReadingGroupViewSet(viewsets.ModelViewSet):
+    permission_classes = [permissions.IsAuthenticated, IsGroupAdmin]
+    queryset = ReadingGroup.objects.prefetch_related("memberships__user")
+
+    def get_serializer_class(self):
+        if self.action == "create":
+            return ReadingGroupCreateSerializer
+        if self.action == "retrieve":
+            return ReadingGroupDetailSerializer
+        return ReadingGroupListSerializer
+
+    def get_queryset(self) -> QuerySet[ReadingGroup]:
+        user = self.request.user
+        return ReadingGroup.objects.filter(
+            memberships__user=user
+        ).prefetch_related("memberships__user").distinct()
+
+    def perform_create(self, serializer: ReadingGroupCreateSerializer) -> ReadingGroup:
+        group = serializer.save(admin=self.request.user)
+        ReadingGroupMembership.objects.create(
+            user=self.request.user, group=group, role=ReadingGroupMembership.Role.ADMIN
+        )
+        return group
+
+    @action(detail=True, methods=["post"], permission_classes=[IsGroupAdmin])
+    def add_member(self, request: Request, pk: int | None = None) -> Response:
+        group = self.get_object()
+        member_serializer = AddMemberSerializer(data=request.data)
+        member_serializer.is_valid(raise_exception=True)
+
+        user_id = member_serializer.validated_data["user_id"]
+        from django.conf import settings
+        User = settings.AUTH_USER_MODEL
+        new_member = get_object_or_404(User, id=user_id)
+
+        if ReadingGroupMembership.objects.filter(group=group, user=new_member).exists():
+            return Response(
+                {"detail": "User is already a member of this group."},
+                status=status.HTTP_409_CONFLICT,
+            )
+
+        membership = ReadingGroupMembership.objects.create(
+            user=new_member, group=group, role=ReadingGroupMembership.Role.MEMBER
+        )
+        from apps.groups.serializers import ReadingGroupMembershipSerializer
+        return Response(
+            ReadingGroupMembershipSerializer(membership).data,
+            status=status.HTTP_201_CREATED,
+        )
+
+    @action(detail=True, methods=["post"], permission_classes=[IsGroupAdmin])
+    def remove_member(self, request: Request, pk: int | None = None) -> Response:
+        group = self.get_object()
+        member_serializer = AddMemberSerializer(data=request.data)
+        member_serializer.is_valid(raise_exception=True)
+
+        user_id = member_serializer.validated_data["user_id"]
+        if user_id == group.admin_id:
+            return Response(
+                {"detail": "Cannot remove the group admin."},
+                status=status.HTTP_400_BAD_REQUEST,
+            )
+
+        deleted, _ = ReadingGroupMembership.objects.filter(
+            group=group, user_id=user_id
+        ).delete()
+        if not deleted:
+            return Response(
+                {"detail": "User is not a member of this group."},
+                status=status.HTTP_404_NOT_FOUND,
+            )
+        return Response(status=status.HTTP_204_NO_CONTENT)
+
+
+class GroupBookViewSet(viewsets.ModelViewSet):
+    permission_classes = [permissions.IsAuthenticated, IsGroupAdmin]
+
+    def get_serializer_class(self):
+        if self.action == "create":
+            return GroupBookCreateSerializer
+        if self.action == "retrieve":
+            return GroupBookDetailSerializer
+        return GroupBookListSerializer
+
+    def get_queryset(self) -> QuerySet[GroupBook]:
+        group_id = self.kwargs.get("group_pk")
+        return GroupBook.objects.filter(
+            group_id=group_id
+        ).select_related("ebook", "ebook__user", "uploaded_by").prefetch_related(
+            "sections", "schedules"
+        )
+
+    def perform_create(self, serializer: GroupBookCreateSerializer) -> GroupBook:
+        group = get_object_or_404(ReadingGroup, id=self.kwargs["group_pk"])
+        ebook = get_object_or_404(EBook, id=serializer.validated_data["ebook_id"])
+        title = serializer.validated_data.get("title") or ebook.title
+
+        # Mark existing active books as replaced
+        GroupBook.objects.filter(group=group, status=GroupBook.Status.ACTIVE).update(
+            status=GroupBook.Status.REPLACED
+        )
+
+        group_book = GroupBook.objects.create(
+            group=group,
+            ebook=ebook,
+            uploaded_by=self.request.user,
+            title=title,
+            status=GroupBook.Status.ACTIVE,
+        )
+
+        # Auto-detect sections
+        try:
+            apply_sections(group_book)
+        except Exception:
+            logger.exception("Auto-section detection failed for group_book %s", group_book.id)
+
+        # Auto-generate schedule
+        try:
+            apply_schedule(group_book)
+        except Exception:
+            logger.exception("Schedule generation failed for group_book %s", group_book.id)
+
+        return group_book
+
+    @action(detail=True, methods=["post"], url_path="detect-sections")
+    def detect_sections_action(self, request: Request, group_pk: int | None = None, pk: int | None = None) -> Response:
+        group_book = self.get_object()
+        try:
+            sections = apply_sections(group_book)
+        except Exception as exc:
+            logger.exception("Section detection failed for group_book %s", group_book.id)
+            return Response({"error": str(exc)}, status=status.HTTP_500_INTERNAL_SERVER_ERROR)
+        return Response(SectionSerializer(sections, many=True).data)
+
+    @action(detail=True, methods=["post"], url_path="adjust-sections")
+    def adjust_sections(self, request: Request, group_pk: int | None = None, pk: int | None = None) -> Response:
+        group_book = self.get_object()
+        adjust_serializer = SectionAdjustSerializer(data=request.data)
+        adjust_serializer.is_valid(raise_exception=True)
+
+        operation = adjust_serializer.validated_data["operation"]
+        section_ids: list[int] = adjust_serializer.validated_data["section_ids"]
+
+        if operation == "merge":
+            if len(section_ids) < 2:
+                return Response(
+                    {"error": "At least 2 section IDs required for merge."},
+                    status=status.HTTP_400_BAD_REQUEST,
+                )
+            sections = list(
+                Section.objects.filter(id__in=section_ids, group_book=group_book).order_by("order")
+            )
+            if len(sections) < 2:
+                return Response(
+                    {"error": "Not enough valid sections found."},
+                    status=status.HTTP_400_BAD_REQUEST,
+                )
+            merged_title = " — ".join(s.title for s in sections)
+            merged_minutes = sum(s.estimated_reading_minutes for s in sections)
+            merged_start = sections[0].start_chapter_index
+            merged_end = sections[-1].end_chapter_index
+            merged_order = sections[0].order
+
+            # Delete old sections
+            Section.objects.filter(id__in=section_ids, group_book=group_book).delete()
+
+            # Create merged section
+            merged = Section.objects.create(
+                group_book=group_book,
+                title=merged_title,
+                order=merged_order,
+                start_chapter_index=merged_start,
+                end_chapter_index=merged_end,
+                estimated_reading_minutes=merged_minutes,
+            )
+            # Reorder remaining sections
+            _renumber_sections(group_book)
+            return Response(SectionSerializer(merged).data)
+
+        if operation == "split":
+            if len(section_ids) != 1:
+                return Response(
+                    {"error": "Exactly 1 section ID required for split."},
+                    status=status.HTTP_400_BAD_REQUEST,
+                )
+            split_at = adjust_serializer.validated_data.get("split_at", 2)
+            section = get_object_or_404(Section, id=section_ids[0], group_book=group_book)
+            chapters = section.end_chapter_index - section.start_chapter_index
+            if chapters < split_at:
+                return Response(
+                    {"error": f"Section only has {chapters} chapters, cannot split into {split_at}."},
+                    status=status.HTTP_400_BAD_REQUEST,
+                )
+
+            # Delete original
+            orig_order = section.order
+            orig_title = section.title
+            section.delete()
+
+            # Create split sections
+            chunk_size = max(1, chapters // split_at)
+            new_sections: list[Section] = []
+            for i in range(split_at):
+                start_idx = section.start_chapter_index + i * chunk_size
+                end_idx = start_idx + chunk_size if i < split_at - 1 else section.end_chapter_index
+                minutes_each = max(1, section.estimated_reading_minutes // split_at)
+                new_sec = Section.objects.create(
+                    group_book=group_book,
+                    title=f"{orig_title} (Part {i + 1})",
+                    order=orig_order + i,
+                    start_chapter_index=start_idx,
+                    end_chapter_index=end_idx,
+                    estimated_reading_minutes=minutes_each,
+                )
+                new_sections.append(new_sec)
+
+            _renumber_sections(group_book)
+            return Response(SectionSerializer(new_sections, many=True).data)
+
+        return Response({"error": "Invalid operation."}, status=status.HTTP_400_BAD_REQUEST)
+
+    @action(detail=True, methods=["get", "post", "delete"], url_path="schedule")
+    def schedule(self, request: Request, group_pk: int | None = None, pk: int | None = None) -> Response:
+        group_book = self.get_object()
+
+        if request.method == "GET":
+            schedules = ReadingSchedule.objects.filter(group_book=group_book).order_by("meeting_number")
+            return Response(ReadingScheduleSerializer(schedules, many=True).data)
+
+        if request.method == "POST":
+            ReadingSchedule.objects.filter(group_book=group_book).delete()
+            num_meetings = int(request.data.get("num_meetings", 4))
+            try:
+                schedules = apply_schedule(group_book, num_meetings=num_meetings)
+            except Exception as exc:
+                logger.exception("Schedule generation failed for group_book %s", group_book.id)
+                return Response({"error": str(exc)}, status=status.HTTP_500_INTERNAL_SERVER_ERROR)
+            return Response(
+                ReadingScheduleSerializer(schedules, many=True).data,
+                status=status.HTTP_201_CREATED,
+            )
+
+        if request.method == "DELETE":
+            ReadingSchedule.objects.filter(group_book=group_book).delete()
+            return Response(status=status.HTTP_204_NO_CONTENT)
+
+    @action(detail=True, methods=["get", "patch"], url_path="progress")
+    def progress(self, request: Request, group_pk: int | None = None, pk: int | None = None) -> Response:
+        group_book = self.get_object()
+
+        if request.method == "GET":
+            progress_records = MemberProgress.objects.filter(
+                group_book=group_book
+            ).select_related("user", "current_section")
+            return Response(MemberProgressSerializer(progress_records, many=True).data)
+
+        # PATCH: update own progress
+        progress_obj, _created = MemberProgress.objects.get_or_create(
+            user=request.user, group_book=group_book,
+        )
+        serializer = MemberProgressSerializer(progress_obj, data=request.data, partial=True)
+        serializer.is_valid(raise_exception=True)
+        serializer.save()
+        return Response(serializer.data)
+
+
+def _renumber_sections(group_book: GroupBook) -> None:
+    """Re-number sections sequentially by their current order."""
+    sections = list(Section.objects.filter(group_book=group_book).order_by("order"))
+    for idx, section in enumerate(sections):
+        if section.order != idx + 1:
+            section.order = idx + 1
+            section.save(update_fields=["order"])

backend/config/django.py

@@ -39,6 +39,7 @@ INSTALLED_APPS = [
     # Local apps
     "apps.users",
     "apps.books",
+    "apps.groups",
     "apps.annotations",
     "apps.reader",
 ]

backend/config/urls.py

@@ -6,6 +6,7 @@ urlpatterns = [
     path("admin/", admin.site.urls),
     path("api/auth/", include("apps.users.urls")),
     path("api/books/", include("apps.books.urls")),
+    path("api/groups/", include("apps.groups.urls")),
     path("api/annotations/", include("apps.annotations.urls")),
     path("api/reader/", include("apps.reader.urls")),
 ]

frontend/src/App.tsx

@@ -12,6 +12,9 @@ const AddBookPage = lazy(() => import("./pages/AddBook").then((m) => ({ default:
 const SettingsPage = lazy(() => import("./pages/Settings").then((m) => ({ default: m.SettingsPage })));
 const BookmarksNotesPage = lazy(() => import("./components/annotations/BookmarksNotesPage").then((m) => ({ default: m.BookmarksNotesPage })));
 const ReadingPage = lazy(() => import("./pages/ReadingPage").then((m) => ({ default: m.default })));
+const GroupsPage = lazy(() => import("./pages/GroupsPage").then((m) => ({ default: m.GroupsPage })));
+const GroupDetailPage = lazy(() => import("./pages/GroupDetailPage").then((m) => ({ default: m.GroupDetailPage })));
+const GroupBookPage = lazy(() => import("./pages/GroupBookPage").then((m) => ({ default: m.GroupBookPage })));
 
 const AuthPage = lazy(() => import("./pages/AuthPage"));
 
@@ -44,6 +47,9 @@ function AppRoutes() {
         <Route path="/reader/:id" element={<ProtectedRoute><ReaderRedirect /></ProtectedRoute>} />
         <Route path="/add" element={<ProtectedRoute><AddBookPage /></ProtectedRoute>} />
         <Route path="/settings" element={<ProtectedRoute><SettingsPage /></ProtectedRoute>} />
+        <Route path="/groups" element={<ProtectedRoute><GroupsPage /></ProtectedRoute>} />
+        <Route path="/groups/:groupId" element={<ProtectedRoute><GroupDetailPage /></ProtectedRoute>} />
+        <Route path="/groups/:groupId/books/:bookId" element={<ProtectedRoute><GroupBookPage /></ProtectedRoute>} />
         <Route path="/bookmarks-notes/:bookId?" element={<ProtectedRoute><BookmarksNotesPage /></ProtectedRoute>} />
         <Route path="*" element={<Navigate to="/" replace />} />
       </Routes>

frontend/src/api/groups.ts

@@ -0,0 +1,151 @@
+import api from "./client";
+import type {
+  AddMemberPayload,
+  AdjustSectionsPayload,
+  CreateGroupBookPayload,
+  CreateGroupPayload,
+  GroupBook,
+  GroupBookDetail,
+  MemberProgress,
+  ReadingGroup,
+  ReadingGroupDetail,
+  ReadingSchedule,
+  Section,
+} from "../types/group";
+
+export const groupsApi = {
+  // ---- Reading Groups ----
+
+  async listGroups(): Promise<ReadingGroup[]> {
+    const { data } = await api.get<{ count: number; results: ReadingGroup[] } | ReadingGroup[]>(
+      "/groups/"
+    );
+    if (Array.isArray(data)) return data;
+    return data.results ?? [];
+  },
+
+  async getGroup(id: number): Promise<ReadingGroupDetail> {
+    const { data } = await api.get<ReadingGroupDetail>(`/groups/${id}/`);
+    return data;
+  },
+
+  async createGroup(payload: CreateGroupPayload): Promise<ReadingGroup> {
+    const { data } = await api.post<ReadingGroup>("/groups/", payload);
+    return data;
+  },
+
+  async deleteGroup(id: number): Promise<void> {
+    await api.delete(`/groups/${id}/`);
+  },
+
+  async addMember(groupId: number, payload: AddMemberPayload): Promise<void> {
+    await api.post(`/groups/${groupId}/add_member/`, payload);
+  },
+
+  async removeMember(groupId: number, payload: AddMemberPayload): Promise<void> {
+    await api.post(`/groups/${groupId}/remove_member/`, payload);
+  },
+
+  // ---- Group Books ----
+
+  async listGroupBooks(groupId: number): Promise<GroupBook[]> {
+    const { data } = await api.get<GroupBook[]>(`/groups/${groupId}/books/`);
+    return Array.isArray(data) ? data : (data as { results: GroupBook[] }).results ?? [];
+  },
+
+  async getGroupBook(groupId: number, bookId: number): Promise<GroupBookDetail> {
+    const { data } = await api.get<GroupBookDetail>(`/groups/${groupId}/books/${bookId}/`);
+    return data;
+  },
+
+  async createGroupBook(
+    groupId: number,
+    payload: CreateGroupBookPayload
+  ): Promise<GroupBookDetail> {
+    const { data } = await api.post<GroupBookDetail>(
+      `/groups/${groupId}/books/`,
+      payload
+    );
+    return data;
+  },
+
+  async deleteGroupBook(groupId: number, bookId: number): Promise<void> {
+    await api.delete(`/groups/${groupId}/books/${bookId}/`);
+  },
+
+  // ---- Sections ----
+
+  async detectSections(
+    groupId: number,
+    bookId: number
+  ): Promise<Section[]> {
+    const { data } = await api.post<Section[]>(
+      `/groups/${groupId}/books/${bookId}/detect-sections/`
+    );
+    return data;
+  },
+
+  async adjustSections(
+    groupId: number,
+    bookId: number,
+    payload: AdjustSectionsPayload
+  ): Promise<Section | Section[]> {
+    const { data } = await api.post<Section | Section[]>(
+      `/groups/${groupId}/books/${bookId}/adjust-sections/`,
+      payload
+    );
+    return data;
+  },
+
+  // ---- Schedule ----
+
+  async getSchedule(
+    groupId: number,
+    bookId: number
+  ): Promise<ReadingSchedule[]> {
+    const { data } = await api.get<ReadingSchedule[]>(
+      `/groups/${groupId}/books/${bookId}/schedule/`
+    );
+    return data;
+  },
+
+  async generateSchedule(
+    groupId: number,
+    bookId: number,
+    numMeetings: number = 4
+  ): Promise<ReadingSchedule[]> {
+    const { data } = await api.post<ReadingSchedule[]>(
+      `/groups/${groupId}/books/${bookId}/schedule/`,
+      { num_meetings: numMeetings }
+    );
+    return data;
+  },
+
+  async deleteSchedule(groupId: number, bookId: number): Promise<void> {
+    await api.delete(`/groups/${groupId}/books/${bookId}/schedule/`);
+  },
+
+  // ---- Progress ----
+
+  async getProgress(
+    groupId: number,
+    bookId: number
+  ): Promise<MemberProgress[]> {
+    const { data } = await api.get<MemberProgress[]>(
+      `/groups/${groupId}/books/${bookId}/progress/`
+    );
+    return data;
+  },
+
+  async updateProgress(
+    groupId: number,
+    bookId: number,
+    payload: { current_section?: number; completed_sections?: number[] }
+  ): Promise<MemberProgress> {
+    const { data } = await api.patch<MemberProgress>(
+      `/groups/${groupId}/books/${bookId}/progress/`,
+      payload
+    );
+    return data;
+  },
+};

frontend/src/locales/en-US.ts

@@ -245,6 +245,54 @@ const enUS = {
     home: "Home",
     bookmarksNotes: "Bookmarks & Notes",
   },
+  groups: {
+    title: "Reading Groups",
+    createGroup: "Create Group",
+    create: "Create",
+    cancel: "Cancel",
+    groupName: "Group Name",
+    groupNamePlaceholder: "Enter group name",
+    description: "Description",
+    descriptionPlaceholder: "What is this group about?",
+    optional: "Optional",
+    noGroups: "No groups yet",
+    noGroupsHint: "Create a reading group to start reading together!",
+    members: "Members",
+    admin: "Admin",
+    addMember: "Add Member",
+    memberIdPlaceholder: "Enter user ID",
+    add: "Add",
+    remove: "Remove",
+    books: "Group Books",
+    uploadEpub: "Upload EPUB",
+    selectEbook: "Select an EPUB to share with the group",
+    noEpubBooks: "No EPUB files uploaded yet",
+    uploadFirst: "Upload an EPUB first",
+    confirmUpload: "Confirm Upload",
+    noBooks: "No books in this group yet",
+    sections: "Sections",
+    schedule: "Schedule",
+    progress: "Progress",
+    detectSections: "Auto-Detect Sections",
+    mergeSections: "Merge Sections",
+    selectSectionsHint: "Click sections to select for merging",
+    merge: "Merge",
+    clear: "Clear",
+    split: "Split",
+    splitInto: "Split into",
+    parts: "parts",
+    splitBtn: "Split",
+    noSections: "No sections detected yet",
+    noSectionsHint: 'Click "Auto-Detect Sections" to parse the EPUB chapters into reading sections.',
+    readingSchedule: "Reading Schedule",
+    generateSchedule: "Generate Schedule",
+    noSchedule: "No schedule generated yet",
+    noScheduleHint: "Detect sections first, then generate a reading schedule for your group.",
+    meeting: "Meeting",
+    memberProgress: "Member Progress",
+    noProgress: "No progress data yet",
+    noProgressHint: "Members will show progress once they start reading.",
+  },
 } as const;
 
 export default enUS;

frontend/src/locales/es-ES.ts

@@ -247,6 +247,54 @@ const esES: Locale = {
     home: "Inicio",
     bookmarksNotes: "Marcadores y notas",
   },
+  groups: {
+    title: "Grupos de Lectura",
+    createGroup: "Crear Grupo",
+    create: "Crear",
+    cancel: "Cancelar",
+    groupName: "Nombre del Grupo",
+    groupNamePlaceholder: "Ingresa el nombre del grupo",
+    description: "Descripción",
+    descriptionPlaceholder: "¿De qué trata este grupo?",
+    optional: "Opcional",
+    noGroups: "Aún no hay grupos",
+    noGroupsHint: "¡Crea un grupo de lectura para leer juntos!",
+    members: "Miembros",
+    admin: "Admin",
+    addMember: "Agregar Miembro",
+    memberIdPlaceholder: "Ingresa ID de usuario",
+    add: "Agregar",
+    remove: "Eliminar",
+    books: "Libros del Grupo",
+    uploadEpub: "Subir EPUB",
+    selectEbook: "Selecciona un EPUB para compartir con el grupo",
+    noEpubBooks: "No hay archivos EPUB subidos aún",
+    uploadFirst: "Sube un EPUB primero",
+    confirmUpload: "Confirmar Subida",
+    noBooks: "No hay libros en este grupo aún",
+    sections: "Secciones",
+    schedule: "Calendario",
+    progress: "Progreso",
+    detectSections: "Auto-Detectar Secciones",
+    mergeSections: "Fusionar Secciones",
+    selectSectionsHint: "Haz clic en las secciones para seleccionar y fusionar",
+    merge: "Fusionar",
+    clear: "Limpiar",
+    split: "Dividir",
+    splitInto: "Dividir en",
+    parts: "partes",
+    splitBtn: "Dividir",
+    noSections: "No se detectaron secciones",
+    noSectionsHint: 'Haz clic en "Auto-Detectar Secciones" para analizar los capítulos del EPUB.',
+    readingSchedule: "Calendario de Lectura",
+    generateSchedule: "Generar Calendario",
+    noSchedule: "No hay calendario generado",
+    noScheduleHint: "Detecta secciones primero, luego genera un calendario de lectura para tu grupo.",
+    meeting: "Reunión",
+    memberProgress: "Progreso de Miembros",
+    noProgress: "Sin datos de progreso",
+    noProgressHint: "Los miembros mostrarán progreso cuando comiencen a leer.",
+  },
 };
 
 export default esES;

frontend/src/pages/GroupBookPage.tsx

@@ -0,0 +1,426 @@
+import React, { useCallback, useEffect, useState } from "react";
+import { useNavigate, useParams } from "react-router-dom";
+import { useTranslation } from "react-i18n-lite";
+import { groupsApi } from "../api/groups";
+import { getApiErrorMessage } from "../api/errors";
+import type {
+  GroupBookDetail,
+  ReadingSchedule,
+  Section,
+  MemberProgress,
+} from "../types/group";
+
+export function GroupBookPage() {
+  const { t } = useTranslation();
+  const navigate = useNavigate();
+  const { groupId, bookId } = useParams<{ groupId: string; bookId: string }>();
+
+  const [book, setBook] = useState<GroupBookDetail | null>(null);
+  const [sections, setSections] = useState<Section[]>([]);
+  const [schedules, setSchedules] = useState<ReadingSchedule[]>([]);
+  const [progress, setProgress] = useState<MemberProgress[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const [tab, setTab] = useState<"sections" | "schedule" | "progress">("sections");
+
+  // Merge state
+  const [selectedForMerge, setSelectedForMerge] = useState<number[]>([]);
+  const [splitSectionId, setSplitSectionId] = useState<number | null>(null);
+  const [splitAt, setSplitAt] = useState(2);
+
+  const gId = Number(groupId);
+  const bId = Number(bookId);
+
+  const loadData = useCallback(async () => {
+    if (!gId || !bId) return;
+    setLoading(true);
+    try {
+      const [bookData, schedData, progData] = await Promise.all([
+        groupsApi.getGroupBook(gId, bId),
+        groupsApi.getSchedule(gId, bId).catch(() => [] as ReadingSchedule[]),
+        groupsApi.getProgress(gId, bId).catch(() => [] as MemberProgress[]),
+      ]);
+      setBook(bookData);
+      setSections(bookData.sections ?? []);
+      setSchedules(schedData);
+      setProgress(progData);
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to load book"));
+    } finally {
+      setLoading(false);
+    }
+  }, [gId, bId]);
+
+  useEffect(() => {
+    loadData();
+  }, [loadData]);
+
+  const handleDetectSections = async () => {
+    if (!gId || !bId) return;
+    try {
+      const newSections = await groupsApi.detectSections(gId, bId);
+      setSections(newSections);
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to detect sections"));
+    }
+  };
+
+  const handleMerge = async () => {
+    if (selectedForMerge.length < 2 || !gId || !bId) return;
+    try {
+      await groupsApi.adjustSections(gId, bId, {
+        operation: "merge",
+        section_ids: selectedForMerge,
+      });
+      setSelectedForMerge([]);
+      await loadData();
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to merge sections"));
+    }
+  };
+
+  const handleSplit = async () => {
+    if (!splitSectionId || !gId || !bId) return;
+    try {
+      await groupsApi.adjustSections(gId, bId, {
+        operation: "split",
+        section_ids: [splitSectionId],
+        split_at: splitAt,
+      });
+      setSplitSectionId(null);
+      await loadData();
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to split section"));
+    }
+  };
+
+  const handleGenerateSchedule = async () => {
+    if (!gId || !bId) return;
+    try {
+      const newSched = await groupsApi.generateSchedule(gId, bId, 4);
+      setSchedules(newSched);
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to generate schedule"));
+    }
+  };
+
+  const toggleMergeSelect = (id: number) => {
+    setSelectedForMerge((prev) =>
+      prev.includes(id) ? prev.filter((s) => s !== id) : [...prev, id]
+    );
+  };
+
+  const formatMinutes = (mins: number): string => {
+    if (mins < 60) return `${mins}m`;
+    const h = Math.floor(mins / 60);
+    const m = mins % 60;
+    return m > 0 ? `${h}h ${m}m` : `${h}h`;
+  };
+
+  if (loading) {
+    return (
+      <div style={{ maxWidth: 800, margin: "0 auto", padding: 16, minHeight: "100vh", background: "#f8f9fa" }}>
+        <p style={{ textAlign: "center", color: "#888", padding: 40 }}>{t("common.loading")}</p>
+      </div>
+    );
+  }
+
+  if (!book) {
+    return (
+      <div style={{ maxWidth: 800, margin: "0 auto", padding: 16, minHeight: "100vh", background: "#f8f9fa" }}>
+        <p style={{ textAlign: "center", color: "#e74c3c", padding: 40 }}>Book not found</p>
+        <button onClick={() => navigate(`/groups/${groupId}`)} style={{ display: "block", margin: "0 auto" }}>← Back</button>
+      </div>
+    );
+  }
+
+  return (
+    <div style={{ maxWidth: 800, margin: "0 auto", padding: 16, minHeight: "100vh", background: "#f8f9fa" }}>
+      {/* Header */}
+      <header style={{ display: "flex", justifyContent: "space-between", alignItems: "center", padding: "16px 0", borderBottom: "1px solid #eee", marginBottom: 20 }}>
+        <div>
+          <h1 style={{ fontSize: 24, fontWeight: 700, color: "#1a1a2e", margin: 0 }}>{book.title}</h1>
+          <p style={{ margin: 4, fontSize: 13, color: "#888" }}>
+            {book.ebook.author && `by ${book.ebook.author} · `}
+            {book.ebook.page_count} chapters · {book.ebook.format.toUpperCase()}
+          </p>
+        </div>
+        <button onClick={() => navigate(`/groups/${groupId}`)} style={{ padding: "8px 16px", borderRadius: 6, border: "1px solid #ddd", background: "#fff", cursor: "pointer", fontSize: 14 }}>
+          ← {t("common.back")}
+        </button>
+      </header>
+
+      {error && (
+        <div style={{ background: "#fde8e8", padding: 12, borderRadius: 6, color: "#e74c3c", fontSize: 14, marginBottom: 16 }}>
+          {error}
+          <button onClick={() => setError(null)} style={{ marginLeft: 12, background: "none", border: "none", cursor: "pointer", fontWeight: 600 }}>✕</button>
+        </div>
+      )}
+
+      {/* Tabs */}
+      <div style={{ display: "flex", gap: 4, marginBottom: 20, background: "#eee", borderRadius: 8, padding: 4 }}>
+        {(["sections", "schedule", "progress"] as const).map((t) => (
+          <button
+            key={t}
+            onClick={() => setTab(t)}
+            style={{
+              flex: 1, padding: "10px 16px", borderRadius: 6, border: "none",
+              fontSize: 14, fontWeight: 600, cursor: "pointer",
+              background: tab === t ? "#fff" : "transparent",
+              color: tab === t ? "#1a1a2e" : "#888",
+              boxShadow: tab === t ? "0 1px 4px rgba(0,0,0,0.1)" : "none",
+            }}
+          >
+            {t === "sections" ? t("groups.sections") : t === "schedule" ? t("groups.schedule") : t("groups.progress")}
+          </button>
+        ))}
+      </div>
+
+      {/* Sections Tab */}
+      {tab === "sections" && (
+        <section>
+          <div style={{ display: "flex", justifyContent: "space-between", alignItems: "center", marginBottom: 16 }}>
+            <h2 style={{ fontSize: 18, fontWeight: 600, color: "#1a1a2e", margin: 0 }}>
+              {sections.length} {t("groups.sections")}
+            </h2>
+            <div style={{ display: "flex", gap: 8 }}>
+              <button
+                onClick={handleDetectSections}
+                style={{ padding: "8px 16px", borderRadius: 6, border: "none", background: "#1a1a2e", color: "#fff", fontSize: 13, fontWeight: 600, cursor: "pointer" }}
+              >
+                {t("groups.detectSections")}
+              </button>
+            </div>
+          </div>
+
+          {/* Merge controls */}
+          <div style={{ background: "#fff", padding: 16, borderRadius: 10, marginBottom: 12, boxShadow: "0 1px 4px rgba(0,0,0,0.06)" }}>
+            <div style={{ display: "flex", alignItems: "center", gap: 10, flexWrap: "wrap" }}>
+              <span style={{ fontSize: 14, fontWeight: 600, color: "#555" }}>{t("groups.mergeSections")}:</span>
+              <span style={{ fontSize: 13, color: "#888" }}>
+                {selectedForMerge.length === 0
+                  ? t("groups.selectSectionsHint")
+                  : `${selectedForMerge.length} selected`}
+              </span>
+              {selectedForMerge.length >= 2 && (
+                <button
+                  onClick={handleMerge}
+                  style={{ padding: "6px 14px", borderRadius: 6, border: "none", background: "#27ae60", color: "#fff", fontSize: 13, fontWeight: 600, cursor: "pointer" }}
+                >
+                  {t("groups.merge")}
+                </button>
+              )}
+              {selectedForMerge.length > 0 && (
+                <button
+                  onClick={() => setSelectedForMerge([])}
+                  style={{ padding: "6px 12px", borderRadius: 6, border: "1px solid #ddd", background: "#fff", fontSize: 13, cursor: "pointer" }}
+                >
+                  {t("groups.clear")}
+                </button>
+              )}
+            </div>
+          </div>
+
+          {sections.length === 0 ? (
+            <div style={{ textAlign: "center", padding: 40, color: "#888" }}>
+              <p style={{ fontSize: 16 }}>{t("groups.noSections")}</p>
+              <p style={{ fontSize: 14 }}>{t("groups.noSectionsHint")}</p>
+            </div>
+          ) : (
+            <div style={{ display: "flex", flexDirection: "column", gap: 10 }}>
+              {sections.map((section) => (
+                <div
+                  key={section.id}
+                  style={{
+                    background: selectedForMerge.includes(section.id) ? "#e8f0fe" : "#fff",
+                    border: selectedForMerge.includes(section.id) ? "2px solid #1a1a2e" : "1px solid #eee",
+                    padding: 16, borderRadius: 10, cursor: "pointer",
+                    boxShadow: "0 1px 4px rgba(0,0,0,0.06)",
+                    transition: "all 0.15s",
+                  }}
+                  onClick={() => toggleMergeSelect(section.id)}
+                >
+                  <div style={{ display: "flex", justifyContent: "space-between", alignItems: "flex-start" }}>
+                    <div style={{ flex: 1 }}>
+                      <div style={{ display: "flex", alignItems: "center", gap: 8 }}>
+                        <span style={{
+                          background: "#1a1a2e", color: "#fff", borderRadius: 20,
+                          width: 26, height: 26, display: "flex", alignItems: "center", justifyContent: "center",
+                          fontSize: 13, fontWeight: 700, flexShrink: 0,
+                        }}>
+                          {section.order}
+                        </span>
+                        <h3 style={{ margin: 0, fontSize: 15, fontWeight: 600, color: "#1a1a2e" }}>{section.title}</h3>
+                      </div>
+                      <p style={{ margin: "6px 0 0 34px", fontSize: 13, color: "#888" }}>
+                        Ch. {section.start_chapter_index}–{section.end_chapter_index - 1} · ~{formatMinutes(section.estimated_reading_minutes)} reading time
+                      </p>
+                    </div>
+                    <button
+                      onClick={(e) => {
+                        e.stopPropagation();
+                        setSplitSectionId(splitSectionId === section.id ? null : section.id);
+                      }}
+                      style={{
+                        padding: "4px 10px", borderRadius: 4, border: "1px solid #ddd",
+                        background: splitSectionId === section.id ? "#1a1a2e" : "#fff",
+                        color: splitSectionId === section.id ? "#fff" : "#666",
+                        fontSize: 12, cursor: "pointer", flexShrink: 0,
+                      }}
+                    >
+                      {t("groups.split")}
+                    </button>
+                  </div>
+                  {splitSectionId === section.id && (
+                    <div
+                      style={{ marginTop: 10, padding: 10, background: "#f8f9fa", borderRadius: 6, display: "flex", alignItems: "center", gap: 8 }}
+                      onClick={(e) => e.stopPropagation()}
+                    >
+                      <span style={{ fontSize: 13 }}>{t("groups.splitInto")}</span>
+                      <input
+                        type="number"
+                        value={splitAt}
+                        min={2}
+                        max={10}
+                        onChange={(e) => setSplitAt(Number(e.target.value))}
+                        style={{ width: 50, padding: "4px 8px", borderRadius: 4, border: "1px solid #ddd", fontSize: 13, textAlign: "center" }}
+                      />
+                      <span style={{ fontSize: 13 }}>{t("groups.parts")}</span>
+                      <button
+                        onClick={handleSplit}
+                        style={{ padding: "4px 12px", borderRadius: 4, border: "none", background: "#1a1a2e", color: "#fff", fontSize: 12, cursor: "pointer" }}
+                      >
+                        {t("groups.splitBtn")}
+                      </button>
+                    </div>
+                  )}
+                </div>
+              ))}
+            </div>
+          )}
+        </section>
+      )}
+
+      {/* Schedule Tab */}
+      {tab === "schedule" && (
+        <section>
+          <div style={{ display: "flex", justifyContent: "space-between", alignItems: "center", marginBottom: 16 }}>
+            <h2 style={{ fontSize: 18, fontWeight: 600, color: "#1a1a2e", margin: 0 }}>
+              {t("groups.readingSchedule")}
+            </h2>
+            <button
+              onClick={handleGenerateSchedule}
+              style={{ padding: "8px 16px", borderRadius: 6, border: "none", background: "#1a1a2e", color: "#fff", fontSize: 13, fontWeight: 600, cursor: "pointer" }}
+            >
+              {t("groups.generateSchedule")}
+            </button>
+          </div>
+
+          {schedules.length === 0 ? (
+            <div style={{ textAlign: "center", padding: 40, color: "#888" }}>
+              <p style={{ fontSize: 16 }}>{t("groups.noSchedule")}</p>
+              <p style={{ fontSize: 14 }}>{t("groups.noScheduleHint")}</p>
+            </div>
+          ) : (
+            <div style={{ display: "flex", flexDirection: "column", gap: 16 }}>
+              {schedules.map((s) => (
+                <div
+                  key={s.id}
+                  style={{ background: "#fff", padding: 20, borderRadius: 12, boxShadow: "0 2px 8px rgba(0,0,0,0.06)" }}
+                >
+                  <div style={{ display: "flex", justifyContent: "space-between", alignItems: "center", marginBottom: 12 }}>
+                    <div>
+                      <h3 style={{ margin: 0, fontSize: 17, fontWeight: 700, color: "#1a1a2e" }}>
+                        {t("groups.meeting")} {s.meeting_number}
+                      </h3>
+                      <p style={{ margin: "4px 0 0", fontSize: 13, color: "#888" }}>
+                        Week of {new Date(s.week_date).toLocaleDateString("en-US", { month: "long", day: "numeric", year: "numeric" })}
+                      </p>
+                    </div>
+                    <span style={{
+                      background: "#f0f0f0", padding: "6px 12px", borderRadius: 20,
+                      fontSize: 13, fontWeight: 600, color: "#555",
+                    }}>
+                      {s.section_details.reduce((sum, sec) => sum + sec.estimated_reading_minutes, 0) > 0
+                        ? `~${formatMinutes(s.section_details.reduce((sum, sec) => sum + sec.estimated_reading_minutes, 0))}`
+                        : ""}
+                    </span>
+                  </div>
+                  <div style={{ display: "flex", flexDirection: "column", gap: 6 }}>
+                    {s.section_details.map((sec) => (
+                      <div
+                        key={sec.id}
+                        style={{
+                          display: "flex", alignItems: "center", gap: 10, padding: "8px 12px",
+                          background: "#f8f9fa", borderRadius: 6, fontSize: 14,
+                        }}
+                      >
+                        <span style={{
+                          background: "#1a1a2e", color: "#fff", borderRadius: 12,
+                          width: 22, height: 22, display: "flex", alignItems: "center", justifyContent: "center",
+                          fontSize: 11, fontWeight: 700, flexShrink: 0,
+                        }}>
+                          {sec.order}
+                        </span>
+                        <span style={{ flex: 1 }}>{sec.title}</span>
+                        <span style={{ fontSize: 12, color: "#999" }}>{formatMinutes(sec.estimated_reading_minutes)}</span>
+                      </div>
+                    ))}
+                  </div>
+                </div>
+              ))}
+            </div>
+          )}
+        </section>
+      )}
+
+      {/* Progress Tab */}
+      {tab === "progress" && (
+        <section>
+          <h2 style={{ fontSize: 18, fontWeight: 600, color: "#1a1a2e", margin: "0 0 16px" }}>
+            {t("groups.memberProgress")}
+          </h2>
+          {progress.length === 0 ? (
+            <div style={{ textAlign: "center", padding: 40, color: "#888" }}>
+              <p style={{ fontSize: 16 }}>{t("groups.noProgress")}</p>
+              <p style={{ fontSize: 14 }}>{t("groups.noProgressHint")}</p>
+            </div>
+          ) : (
+            <div style={{ display: "flex", flexDirection: "column", gap: 10 }}>
+              {progress.map((p) => {
+                const totalSections = sections.length;
+                const completed = p.completed_sections.length;
+                const pct = totalSections > 0 ? Math.round((completed / totalSections) * 100) : 0;
+                return (
+                  <div
+                    key={p.id}
+                    style={{ background: "#fff", padding: 16, borderRadius: 10, boxShadow: "0 1px 4px rgba(0,0,0,0.06)" }}
+                  >
+                    <div style={{ display: "flex", justifyContent: "space-between", alignItems: "center", marginBottom: 8 }}>
+                      <span style={{ fontSize: 15, fontWeight: 600 }}>{p.user_email}</span>
+                      <span style={{ fontSize: 13, color: "#888" }}>{completed}/{totalSections} · {pct}%</span>
+                    </div>
+                    <div style={{ height: 6, background: "#eee", borderRadius: 3, overflow: "hidden" }}>
+                      <div
+                        style={{
+                          height: "100%", borderRadius: 3,
+                          background: "linear-gradient(90deg, #27ae60, #2ecc71)",
+                          width: `${pct}%`, transition: "width 0.3s",
+                        }}
+                      />
+                    </div>
+                    {p.current_section_title && (
+                      <p style={{ margin: "8px 0 0", fontSize: 13, color: "#888" }}>
+                        Currently: {p.current_section_title}
+                      </p>
+                    )}
+                  </div>
+                );
+              })}
+            </div>
+          )}
+        </section>
+      )}
+    </div>
+  );
+}

frontend/src/pages/GroupDetailPage.tsx

@@ -0,0 +1,300 @@
+import React, { useCallback, useEffect, useState } from "react";
+import { useNavigate, useParams } from "react-router-dom";
+import { useTranslation } from "react-i18n-lite";
+import { groupsApi } from "../api/groups";
+import { booksApi } from "../api/books";
+import { getApiErrorMessage } from "../api/errors";
+import type { ReadingGroupDetail, GroupBook, GroupBookDetail } from "../types/group";
+import type { EBookListItem } from "../types/book";
+
+export function GroupDetailPage() {
+  const { t } = useTranslation();
+  const navigate = useNavigate();
+  const { groupId } = useParams<{ groupId: string }>();
+  const [group, setGroup] = useState<ReadingGroupDetail | null>(null);
+  const [books, setBooks] = useState<GroupBook[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  // Upload state
+  const [showUpload, setShowUpload] = useState(false);
+  const [ebooks, setEbooks] = useState<EBookListItem[]>([]);
+  const [selectedEbookId, setSelectedEbookId] = useState<number | null>(null);
+  const [uploading, setUploading] = useState(false);
+
+  // Add member state
+  const [showAddMember, setShowAddMember] = useState(false);
+  const [memberEmail, setMemberEmail] = useState("");
+  const [adding, setAdding] = useState(false);
+
+  const id = Number(groupId);
+
+  const loadData = useCallback(async () => {
+    if (!id) return;
+    setLoading(true);
+    try {
+      const [groupData, bookData] = await Promise.all([
+        groupsApi.getGroup(id),
+        groupsApi.listGroupBooks(id),
+      ]);
+      setGroup(groupData);
+      setBooks(bookData);
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to load group"));
+    } finally {
+      setLoading(false);
+    }
+  }, [id]);
+
+  useEffect(() => {
+    loadData();
+  }, [loadData]);
+
+  const handleUploadClick = async () => {
+    setShowUpload(true);
+    try {
+      const ebookList = await booksApi.getEBooks();
+      setEbooks(ebookList.filter((e) => e.format === "epub"));
+    } catch {
+      // Ebook list fetch failed silently
+    }
+  };
+
+  const handleUpload = async () => {
+    if (!selectedEbookId || !id) return;
+    setUploading(true);
+    try {
+      const created = await groupsApi.createGroupBook(id, { ebook_id: selectedEbookId });
+      setShowUpload(false);
+      setSelectedEbookId(null);
+      await loadData();
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to upload book to group"));
+    } finally {
+      setUploading(false);
+    }
+  };
+
+  const handleAddMember = async (e: React.FormEvent) => {
+    e.preventDefault();
+    if (!memberEmail.trim() || !id) return;
+    setAdding(true);
+    try {
+      // Note: In a real implementation, we'd look up user by email.
+      // For now this requires user_id. Email lookup would be an enhancement.
+      await groupsApi.addMember(id, { user_id: Number(memberEmail) });
+      setShowAddMember(false);
+      setMemberEmail("");
+      await loadData();
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to add member. Please use a valid user ID."));
+    } finally {
+      setAdding(false);
+    }
+  };
+
+  const handleRemoveMember = async (userId: number) => {
+    if (!id) return;
+    try {
+      await groupsApi.removeMember(id, { user_id: userId });
+      await loadData();
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to remove member"));
+    }
+  };
+
+  if (loading) {
+    return (
+      <div style={{ maxWidth: 700, margin: "0 auto", padding: 16, minHeight: "100vh", background: "#f8f9fa" }}>
+        <p style={{ textAlign: "center", color: "#888", padding: 40 }}>{t("common.loading")}</p>
+      </div>
+    );
+  }
+
+  if (!group) {
+    return (
+      <div style={{ maxWidth: 700, margin: "0 auto", padding: 16, minHeight: "100vh", background: "#f8f9fa" }}>
+        <p style={{ textAlign: "center", color: "#e74c3c", padding: 40 }}>Group not found</p>
+        <button onClick={() => navigate("/groups")} style={{ display: "block", margin: "0 auto" }}>← Back to Groups</button>
+      </div>
+    );
+  }
+
+  return (
+    <div style={{ maxWidth: 700, margin: "0 auto", padding: 16, minHeight: "100vh", background: "#f8f9fa" }}>
+      <header style={{ display: "flex", justifyContent: "space-between", alignItems: "center", padding: "16px 0", borderBottom: "1px solid #eee", marginBottom: 20 }}>
+        <div>
+          <h1 style={{ fontSize: 24, fontWeight: 700, color: "#1a1a2e", margin: 0 }}>{group.name}</h1>
+          {group.description && <p style={{ margin: "4px 0 0", fontSize: 14, color: "#666" }}>{group.description}</p>}
+        </div>
+        <button onClick={() => navigate("/groups")} style={{ padding: "8px 16px", borderRadius: 6, border: "1px solid #ddd", background: "#fff", cursor: "pointer", fontSize: 14 }}>
+          ← {t("common.back")}
+        </button>
+      </header>
+
+      {error && (
+        <div style={{ background: "#fde8e8", padding: 12, borderRadius: 6, color: "#e74c3c", fontSize: 14, marginBottom: 16 }}>
+          {error}
+          <button onClick={() => setError(null)} style={{ marginLeft: 12, background: "none", border: "none", cursor: "pointer", fontWeight: 600 }}>✕</button>
+        </div>
+      )}
+
+      {/* Members Section */}
+      <section style={{ background: "#fff", padding: 20, borderRadius: 12, marginBottom: 20, boxShadow: "0 2px 8px rgba(0,0,0,0.06)" }}>
+        <div style={{ display: "flex", justifyContent: "space-between", alignItems: "center", marginBottom: 12 }}>
+          <h2 style={{ fontSize: 18, fontWeight: 600, color: "#1a1a2e", margin: 0 }}>{t("groups.members")} ({group.members.length})</h2>
+          <button
+            onClick={() => setShowAddMember(!showAddMember)}
+            style={{ padding: "6px 14px", borderRadius: 6, border: "1px solid #ddd", background: "#fff", cursor: "pointer", fontSize: 13 }}
+          >
+            {showAddMember ? t("groups.cancel") : `+ ${t("groups.addMember")}`}
+          </button>
+        </div>
+        {showAddMember && (
+          <form onSubmit={handleAddMember} style={{ display: "flex", gap: 8, marginBottom: 12 }}>
+            <input
+              type="text"
+              value={memberEmail}
+              onChange={(e) => setMemberEmail(e.target.value)}
+              placeholder={t("groups.memberIdPlaceholder")}
+              style={{ flex: 1, padding: "8px 12px", borderRadius: 6, border: "1px solid #ddd", fontSize: 14, outline: "none" }}
+            />
+            <button
+              type="submit"
+              disabled={adding}
+              style={{ padding: "8px 16px", borderRadius: 6, border: "none", background: "#1a1a2e", color: "#fff", fontSize: 14, cursor: "pointer", opacity: adding ? 0.6 : 1 }}
+            >
+              {t("groups.add")}
+            </button>
+          </form>
+        )}
+        <div style={{ display: "flex", flexDirection: "column", gap: 8 }}>
+          {group.members.map((m) => (
+            <div key={m.id} style={{ display: "flex", justifyContent: "space-between", alignItems: "center", padding: "8px 0", borderBottom: "1px solid #f0f0f0" }}>
+              <div>
+                <span style={{ fontSize: 14, fontWeight: 500 }}>{m.user_email}</span>
+                <span style={{ marginLeft: 8, fontSize: 12, color: m.role === "admin" ? "#e67e22" : "#999", background: m.role === "admin" ? "#fef3e2" : "#f0f0f0", padding: "2px 8px", borderRadius: 4 }}>
+                  {m.role}
+                </span>
+              </div>
+              {m.role !== "admin" && (
+                <button
+                  onClick={() => handleRemoveMember(m.user)}
+                  style={{ background: "none", border: "none", color: "#e74c3c", cursor: "pointer", fontSize: 13 }}
+                >
+                  {t("groups.remove")}
+                </button>
+              )}
+            </div>
+          ))}
+        </div>
+      </section>
+
+      {/* Books Section */}
+      <section style={{ background: "#fff", padding: 20, borderRadius: 12, boxShadow: "0 2px 8px rgba(0,0,0,0.06)" }}>
+        <div style={{ display: "flex", justifyContent: "space-between", alignItems: "center", marginBottom: 12 }}>
+          <h2 style={{ fontSize: 18, fontWeight: 600, color: "#1a1a2e", margin: 0 }}>{t("groups.books")} ({books.length})</h2>
+          <button
+            onClick={handleUploadClick}
+            style={{ padding: "8px 18px", borderRadius: 8, border: "none", background: "#1a1a2e", color: "#fff", fontSize: 14, fontWeight: 600, cursor: "pointer" }}
+          >
+            {t("groups.uploadEpub")}
+          </button>
+        </div>
+
+        {showUpload && (
+          <div style={{ background: "#f8f9fa", padding: 16, borderRadius: 8, marginBottom: 16 }}>
+            <h3 style={{ fontSize: 15, fontWeight: 600, margin: "0 0 12px" }}>{t("groups.selectEbook")}</h3>
+            {ebooks.length === 0 ? (
+              <div style={{ textAlign: "center", padding: 20, color: "#888" }}>
+                <p>{t("groups.noEpubBooks")}</p>
+                <button onClick={() => navigate("/add")} style={{ marginTop: 8, padding: "8px 16px", borderRadius: 6, border: "1px solid #ddd", background: "#fff", cursor: "pointer", fontSize: 13 }}>
+                  {t("groups.uploadFirst")}
+                </button>
+              </div>
+            ) : (
+              <div>
+                <div style={{ display: "flex", flexDirection: "column", gap: 8, marginBottom: 12, maxHeight: 200, overflowY: "auto" }}>
+                  {ebooks.map((eb) => (
+                    <label
+                      key={eb.id}
+                      style={{
+                        display: "flex", alignItems: "center", gap: 10, padding: "10px 12px",
+                        borderRadius: 8, cursor: "pointer", fontSize: 14,
+                        background: selectedEbookId === eb.id ? "#e8f0fe" : "#fff",
+                        border: selectedEbookId === eb.id ? "2px solid #1a1a2e" : "1px solid #eee",
+                      }}
+                    >
+                      <input
+                        type="radio"
+                        name="ebook"
+                        value={eb.id}
+                        checked={selectedEbookId === eb.id}
+                        onChange={() => setSelectedEbookId(eb.id)}
+                        style={{ accentColor: "#1a1a2e" }}
+                      />
+                      <div>
+                        <strong>{eb.title}</strong>
+                        {eb.author && <span style={{ color: "#888", marginLeft: 8 }}>by {eb.author}</span>}
+                        <span style={{ marginLeft: 8, fontSize: 12, color: "#aaa" }}>({eb.filename})</span>
+                      </div>
+                    </label>
+                  ))}
+                </div>
+                <div style={{ display: "flex", gap: 8 }}>
+                  <button
+                    onClick={handleUpload}
+                    disabled={!selectedEbookId || uploading}
+                    style={{ padding: "10px 20px", borderRadius: 8, border: "none", background: "#1a1a2e", color: "#fff", fontSize: 14, fontWeight: 600, cursor: uploading ? "default" : "pointer", opacity: uploading ? 0.6 : 1 }}
+                  >
+                    {uploading ? t("common.loading") : t("groups.confirmUpload")}
+                  </button>
+                  <button
+                    onClick={() => setShowUpload(false)}
+                    style={{ padding: "10px 20px", borderRadius: 8, border: "1px solid #ddd", background: "#fff", cursor: "pointer", fontSize: 14 }}
+                  >
+                    {t("groups.cancel")}
+                  </button>
+                </div>
+              </div>
+            )}
+          </div>
+        )}
+
+        {books.length === 0 ? (
+          <p style={{ textAlign: "center", color: "#888", padding: 30 }}>{t("groups.noBooks")}</p>
+        ) : (
+          <div style={{ display: "flex", flexDirection: "column", gap: 10 }}>
+            {books.map((book) => (
+              <div
+                key={book.id}
+                onClick={() => navigate(`/groups/${groupId}/books/${book.id}`)}
+                style={{
+                  display: "flex", justifyContent: "space-between", alignItems: "center",
+                  padding: 16, borderRadius: 10, cursor: "pointer", transition: "background 0.2s",
+                  background: book.status === "active" ? "#f0faf0" : "#fafafa",
+                  border: book.status === "active" ? "2px solid #27ae60" : "1px solid #eee",
+                }}
+                onMouseEnter={(e) => (e.currentTarget.style.background = book.status === "active" ? "#e8f5e9" : "#f5f5f5")}
+                onMouseLeave={(e) => (e.currentTarget.style.background = book.status === "active" ? "#f0faf0" : "#fafafa")}
+              >
+                <div>
+                  <h3 style={{ margin: 0, fontSize: 16, fontWeight: 600, color: "#1a1a2e" }}>
+                    {book.title}
+                    {book.status === "active" && (
+                      <span style={{ marginLeft: 8, fontSize: 11, color: "#27ae60", background: "#e8f5e9", padding: "2px 8px", borderRadius: 4 }}>Active</span>
+                    )}
+                  </h3>
+                  <p style={{ margin: "4px 0 0", fontSize: 13, color: "#888" }}>
+                    {book.section_count} sections · {book.ebook.page_count} chapters · uploaded by {book.uploaded_by_email}
+                  </p>
+                </div>
+                <span style={{ fontSize: 20, color: "#ccc" }}>→</span>
+              </div>
+            ))}
+          </div>
+        )}
+      </section>
+    </div>
+  );
+}

frontend/src/pages/GroupsPage.tsx

@@ -0,0 +1,162 @@
+import React, { useCallback, useEffect, useState } from "react";
+import { useNavigate } from "react-router-dom";
+import { useTranslation } from "react-i18n-lite";
+import { groupsApi } from "../api/groups";
+import { getApiErrorMessage } from "../api/errors";
+import type { ReadingGroup } from "../types/group";
+
+export function GroupsPage() {
+  const { t } = useTranslation();
+  const navigate = useNavigate();
+  const [groups, setGroups] = useState<ReadingGroup[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const [showCreate, setShowCreate] = useState(false);
+  const [newName, setNewName] = useState("");
+  const [newDesc, setNewDesc] = useState("");
+  const [creating, setCreating] = useState(false);
+
+  const loadGroups = useCallback(async () => {
+    setLoading(true);
+    try {
+      const data = await groupsApi.listGroups();
+      setGroups(data);
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to load groups"));
+    } finally {
+      setLoading(false);
+    }
+  }, []);
+
+  useEffect(() => {
+    loadGroups();
+  }, [loadGroups]);
+
+  const handleCreate = async (e: React.FormEvent) => {
+    e.preventDefault();
+    if (!newName.trim()) return;
+    setCreating(true);
+    try {
+      await groupsApi.createGroup({ name: newName.trim(), description: newDesc.trim() });
+      setShowCreate(false);
+      setNewName("");
+      setNewDesc("");
+      await loadGroups();
+    } catch (err) {
+      setError(getApiErrorMessage(err, "Failed to create group"));
+    } finally {
+      setCreating(false);
+    }
+  };
+
+  return (
+    <div style={{ maxWidth: 700, margin: "0 auto", padding: 16, minHeight: "100vh", background: "#f8f9fa" }}>
+      <header style={{ display: "flex", justifyContent: "space-between", alignItems: "center", padding: "16px 0", borderBottom: "1px solid #eee", marginBottom: 20 }}>
+        <h1 style={{ fontSize: 24, fontWeight: 700, color: "#1a1a2e", margin: 0 }}>{t("groups.title")}</h1>
+        <button
+          type="button"
+          onClick={() => navigate("/")}
+          style={{ padding: "8px 16px", borderRadius: 6, border: "1px solid #ddd", background: "#fff", cursor: "pointer", fontSize: 14 }}
+        >
+          ← {t("common.back")}
+        </button>
+      </header>
+
+      {error && (
+        <div style={{ background: "#fde8e8", padding: 12, borderRadius: 6, color: "#e74c3c", fontSize: 14, marginBottom: 16 }}>
+          {error}
+          <button onClick={() => setError(null)} style={{ marginLeft: 12, background: "none", border: "none", cursor: "pointer", fontWeight: 600 }}>✕</button>
+        </div>
+      )}
+
+      <div style={{ marginBottom: 20 }}>
+        <button
+          type="button"
+          onClick={() => setShowCreate(!showCreate)}
+          style={{
+            padding: "12px 24px", borderRadius: 8, border: "none",
+            background: "#1a1a2e", color: "#fff", fontSize: 15, fontWeight: 600, cursor: "pointer",
+          }}
+        >
+          {showCreate ? t("groups.cancel") : t("groups.createGroup")}
+        </button>
+      </div>
+
+      {showCreate && (
+        <form onSubmit={handleCreate} style={{
+          background: "#fff", padding: 20, borderRadius: 12, marginBottom: 24,
+          boxShadow: "0 2px 8px rgba(0,0,0,0.06)", display: "flex", flexDirection: "column", gap: 14,
+        }}>
+          <div style={{ display: "flex", flexDirection: "column", gap: 6 }}>
+            <label style={{ fontSize: 14, fontWeight: 600, color: "#555" }}>{t("groups.groupName")}</label>
+            <input
+              type="text"
+              value={newName}
+              onChange={(e) => setNewName(e.target.value)}
+              placeholder={t("groups.groupNamePlaceholder")}
+              style={{ padding: "10px 12px", borderRadius: 6, border: "1px solid #ddd", fontSize: 16, outline: "none" }}
+              required
+            />
+          </div>
+          <div style={{ display: "flex", flexDirection: "column", gap: 6 }}>
+            <label style={{ fontSize: 14, fontWeight: 600, color: "#555" }}>{t("groups.description")} ({t("common.optional")})</label>
+            <textarea
+              value={newDesc}
+              onChange={(e) => setNewDesc(e.target.value)}
+              placeholder={t("groups.descriptionPlaceholder")}
+              rows={3}
+              style={{ padding: "10px 12px", borderRadius: 6, border: "1px solid #ddd", fontSize: 15, outline: "none", resize: "vertical" }}
+            />
+          </div>
+          <button
+            type="submit"
+            disabled={creating || !newName.trim()}
+            style={{
+              padding: "10px 20px", borderRadius: 8, border: "none",
+              background: "#1a1a2e", color: "#fff", fontSize: 15, fontWeight: 600,
+              cursor: creating ? "default" : "pointer", opacity: creating ? 0.6 : 1, alignSelf: "flex-start",
+            }}
+          >
+            {creating ? t("common.loading") : t("groups.create")}
+          </button>
+        </form>
+      )}
+
+      {loading ? (
+        <p style={{ textAlign: "center", color: "#888", padding: 40 }}>{t("common.loading")}</p>
+      ) : groups.length === 0 ? (
+        <div style={{ textAlign: "center", padding: 40, color: "#888" }}>
+          <p style={{ fontSize: 16, marginBottom: 8 }}>{t("groups.noGroups")}</p>
+          <p style={{ fontSize: 14 }}>{t("groups.noGroupsHint")}</p>
+        </div>
+      ) : (
+        <div style={{ display: "flex", flexDirection: "column", gap: 12 }}>
+          {groups.map((group) => (
+            <div
+              key={group.id}
+              onClick={() => navigate(`/groups/${group.id}`)}
+              style={{
+                background: "#fff", padding: 20, borderRadius: 12, cursor: "pointer",
+                boxShadow: "0 2px 8px rgba(0,0,0,0.06)", transition: "box-shadow 0.2s",
+                display: "flex", justifyContent: "space-between", alignItems: "center",
+              }}
+              onMouseEnter={(e) => (e.currentTarget.style.boxShadow = "0 4px 16px rgba(0,0,0,0.1)")}
+              onMouseLeave={(e) => (e.currentTarget.style.boxShadow = "0 2px 8px rgba(0,0,0,0.06)")}
+            >
+              <div>
+                <h3 style={{ margin: 0, fontSize: 18, fontWeight: 600, color: "#1a1a2e" }}>{group.name}</h3>
+                {group.description && (
+                  <p style={{ margin: "6px 0 0", fontSize: 14, color: "#666" }}>{group.description}</p>
+                )}
+                <p style={{ margin: "8px 0 0", fontSize: 13, color: "#999" }}>
+                  {group.member_count} {t("groups.members")} · {t("groups.admin")}: {group.admin_email}
+                </p>
+              </div>
+              <span style={{ fontSize: 20, color: "#ccc" }}>→</span>
+            </div>
+          ))}
+        </div>
+      )}
+    </div>
+  );
+}

frontend/src/types/group.ts

@@ -0,0 +1,109 @@
+/** Types for reading groups, group books, sections, and schedules */
+
+export interface ReadingGroup {
+  id: number;
+  name: string;
+  description: string;
+  admin: number;
+  admin_email: string;
+  member_count: number;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface ReadingGroupDetail {
+  id: number;
+  name: string;
+  description: string;
+  admin: number;
+  admin_email: string;
+  members: GroupMembership[];
+  created_at: string;
+  updated_at: string;
+}
+
+export interface GroupMembership {
+  id: number;
+  user: number;
+  user_email: string;
+  user_username: string;
+  role: "admin" | "member";
+  joined_at: string;
+}
+
+export interface GroupBook {
+  id: number;
+  title: string;
+  status: "active" | "replaced";
+  ebook: {
+    id: number;
+    title: string;
+    author: string;
+    filename: string;
+    format: string;
+    page_count: number;
+    file_size: number;
+    cover_image: string | null;
+    created_at: string;
+  };
+  uploaded_by: number;
+  uploaded_by_email: string;
+  section_count: number;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface Section {
+  id: number;
+  title: string;
+  order: number;
+  start_chapter_index: number;
+  end_chapter_index: number;
+  estimated_reading_minutes: number;
+  created_at: string;
+}
+
+export interface GroupBookDetail extends GroupBook {
+  sections: Section[];
+  schedules: ReadingSchedule[];
+}
+
+export interface ReadingSchedule {
+  id: number;
+  meeting_number: number;
+  week_date: string;
+  section_ids: number[];
+  section_details: Section[];
+  created_at: string;
+}
+
+export interface MemberProgress {
+  id: number;
+  user: number;
+  user_email: string;
+  user_username: string;
+  current_section: number | null;
+  current_section_title: string | null;
+  completed_sections: number[];
+  updated_at: string;
+}
+
+export interface CreateGroupPayload {
+  name: string;
+  description?: string;
+}
+
+export interface AddMemberPayload {
+  user_id: number;
+}
+
+export interface CreateGroupBookPayload {
+  ebook_id: number;
+  title?: string;
+}
+
+export interface AdjustSectionsPayload {
+  operation: "merge" | "split";
+  section_ids: number[];
+  split_at?: number;
+}

packages/shared/src/types.ts

@@ -216,3 +216,47 @@ export interface ApiError {
   detail?: string;
   [key: string]: unknown;
 }
+
+// ---- Reading Groups ----
+
+export interface ReadingGroup {
+  id: number;
+  name: string;
+  description: string;
+  admin: number;
+  admin_email: string;
+  member_count: number;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface GroupMembership {
+  id: number;
+  user: number;
+  user_email: string;
+  user_username: string;
+  role: "admin" | "member";
+  joined_at: string;
+}
+
+export interface GroupBookSummary {
+  id: number;
+  title: string;
+  status: "active" | "replaced";
+  section_count: number;
+  created_at: string;
+}
+
+export interface SectionSummary {
+  id: number;
+  title: string;
+  order: number;
+  estimated_reading_minutes: number;
+}
+
+export interface ReadingScheduleEntry {
+  id: number;
+  meeting_number: number;
+  week_date: string;
+  section_ids: number[];
+}

packages/shared/src/utils.ts

@@ -114,4 +114,14 @@ export const API_ENDPOINTS = {
     bookmarkDetail: (id: string) => `/api/annotations/bookmarks/${id}/`,
     noteDetail: (id: string) => `/api/annotations/notes/${id}/`,
   },
+  groups: {
+    list: "/api/groups/",
+    detail: (id: number) => `/api/groups/${id}/`,
+    books: (groupId: number) => `/api/groups/${groupId}/books/`,
+    bookDetail: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/`,
+    detectSections: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/detect-sections/`,
+    adjustSections: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/adjust-sections/`,
+    schedule: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/schedule/`,
+    progress: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/progress/`,
+  },
 } as const;