feat: Normalized /topics and /videos endpoints from bare lists to pagin…

- "backend/schemas.py"
- "backend/routers/topics.py"
- "backend/routers/videos.py"
- "frontend/src/api/topics.ts"
- "frontend/src/pages/TopicsBrowse.tsx"
- "frontend/src/pages/Home.tsx"

GSD-Task: S05/T03

backend/routers/topics.py

@@ -18,6 +18,7 @@ from schemas import (
     PaginatedResponse,
     TechniquePageRead,
     TopicCategory,
+    TopicListResponse,
     TopicSubTopic,
 )
 
@@ -41,10 +42,10 @@ def _load_canonical_tags() -> list[dict[str, Any]]:
         return []
 
 
-@router.get("", response_model=list[TopicCategory])
+@router.get("", response_model=TopicListResponse)
 async def list_topics(
     db: AsyncSession = Depends(get_session),
-) -> list[TopicCategory]:
+) -> TopicListResponse:
     """Return the two-level topic hierarchy with technique/creator counts per sub-topic.
 
     Categories come from ``canonical_tags.yaml``. Counts are computed
@@ -97,7 +98,7 @@ async def list_topics(
             )
         )
 
-    return result
+    return TopicListResponse(items=result, total=len(result))
 
 
 @router.get("/{category_slug}/{subtopic_slug}", response_model=PaginatedResponse)

backend/routers/videos.py

@@ -4,33 +4,43 @@ import logging
 from typing import Annotated
 
 from fastapi import APIRouter, Depends, Query
-from sqlalchemy import select
+from sqlalchemy import func, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from database import get_session
 from models import SourceVideo
-from schemas import SourceVideoRead
+from schemas import SourceVideoRead, VideoListResponse
 
 logger = logging.getLogger("chrysopedia.videos")
 
 router = APIRouter(prefix="/videos", tags=["videos"])
 
 
-@router.get("", response_model=list[SourceVideoRead])
+@router.get("", response_model=VideoListResponse)
 async def list_videos(
     offset: Annotated[int, Query(ge=0)] = 0,
     limit: Annotated[int, Query(ge=1, le=100)] = 50,
     creator_id: str | None = None,
     db: AsyncSession = Depends(get_session),
-) -> list[SourceVideoRead]:
+) -> VideoListResponse:
     """List source videos with optional filtering by creator."""
-    stmt = select(SourceVideo).order_by(SourceVideo.created_at.desc())
+    base_stmt = select(SourceVideo).order_by(SourceVideo.created_at.desc())
 
     if creator_id:
-        stmt = stmt.where(SourceVideo.creator_id == creator_id)
+        base_stmt = base_stmt.where(SourceVideo.creator_id == creator_id)
 
-    stmt = stmt.offset(offset).limit(limit)
+    # Total count (before offset/limit)
+    count_stmt = select(func.count()).select_from(base_stmt.subquery())
+    count_result = await db.execute(count_stmt)
+    total = count_result.scalar() or 0
+
+    stmt = base_stmt.offset(offset).limit(limit)
     result = await db.execute(stmt)
     videos = result.scalars().all()
     logger.debug("Listed %d videos (offset=%d, limit=%d)", len(videos), offset, limit)
-    return [SourceVideoRead.model_validate(v) for v in videos]
+    return VideoListResponse(
+        items=[SourceVideoRead.model_validate(v) for v in videos],
+        total=total,
+        offset=offset,
+        limit=limit,
+    )

backend/schemas.py

@@ -380,6 +380,20 @@ class TopicCategory(BaseModel):
     sub_topics: list[TopicSubTopic] = Field(default_factory=list)
 
 
+class TopicListResponse(BaseModel):
+    """Paginated list of topic categories."""
+    items: list[TopicCategory] = Field(default_factory=list)
+    total: int = 0
+
+
+class VideoListResponse(BaseModel):
+    """Paginated list of source videos."""
+    items: list[SourceVideoRead] = Field(default_factory=list)
+    total: int = 0
+    offset: int = 0
+    limit: int = 50
+
+
 # ── Creator Browse ───────────────────────────────────────────────────────────
 
 class CreatorBrowseItem(CreatorRead):

frontend/src/api/topics.ts

@@ -15,10 +15,15 @@ export interface TopicCategory {
   sub_topics: TopicSubTopic[];
 }
 
+export interface TopicListResponse {
+  items: TopicCategory[];
+  total: number;
+}
+
 // ── Functions ────────────────────────────────────────────────────────────────
 
-export async function fetchTopics(): Promise<TopicCategory[]> {
-  return request<TopicCategory[]>(`${BASE}/topics`);
+export async function fetchTopics(): Promise<TopicListResponse> {
+  return request<TopicListResponse>(`${BASE}/topics`);
 }
 
 export async function fetchSubTopicTechniques(

frontend/src/pages/Home.tsx

@@ -92,7 +92,8 @@ export default function Home() {
     let cancelled = false;
     void (async () => {
       try {
-        const categories = await fetchTopics();
+        const data = await fetchTopics();
+        const categories = data.items;
         const all = categories.flatMap((cat) =>
           cat.sub_topics.map((st) => ({ name: st.name, count: st.technique_count }))
         );

frontend/src/pages/TopicsBrowse.tsx

@@ -35,7 +35,7 @@ export default function TopicsBrowse() {
       try {
         const data = await fetchTopics();
         if (!cancelled) {
-          setCategories(data);
+          setCategories(data.items);
           // Start collapsed
           setExpanded(new Set());
         }