fc3e: /api/posts blueprint — list (with cursor + filters) + detail

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/api/posts.py

@@ -0,0 +1,69 @@
+"""FC-3e: /api/posts — cursor-paginated unified posts feed."""
+
+from quart import Blueprint, jsonify, request
+
+from ..extensions import get_session
+from ..services.post_feed_service import PostFeedService
+from ..services.source_service import KNOWN_PLATFORMS
+
+posts_bp = Blueprint("posts", __name__, url_prefix="/api/posts")
+
+
+def _bad(error: str, *, status: int = 400, detail: str | None = None, **extra):
+    body = {"error": error}
+    if detail is not None:
+        body["detail"] = detail
+    body.update(extra)
+    return jsonify(body), status
+
+
+@posts_bp.route("", methods=["GET"])
+async def list_posts():
+    args = request.args
+
+    cursor = args.get("cursor") or None
+    artist_id_raw = args.get("artist_id")
+    platform = args.get("platform") or None
+    limit_raw = args.get("limit", "24")
+
+    try:
+        limit = int(limit_raw)
+    except ValueError:
+        return _bad("invalid_limit", detail="limit must be an integer")
+    if limit < 1 or limit > 100:
+        return _bad("invalid_limit", detail="limit must be between 1 and 100")
+
+    artist_id = None
+    if artist_id_raw is not None:
+        try:
+            artist_id = int(artist_id_raw)
+        except ValueError:
+            return _bad("invalid_artist_id", detail="artist_id must be an integer")
+
+    if platform is not None and platform not in KNOWN_PLATFORMS:
+        return _bad(
+            "unknown_platform",
+            detail=f"platform must be one of {sorted(KNOWN_PLATFORMS)}",
+        )
+
+    async with get_session() as session:
+        try:
+            page = await PostFeedService(session).scroll(
+                cursor=cursor, artist_id=artist_id,
+                platform=platform, limit=limit,
+            )
+        except ValueError as exc:
+            # Service raises ValueError for malformed cursors only;
+            # limit bounds are validated above.
+            return _bad("invalid_cursor", detail=str(exc))
+
+    return jsonify(page)
+
+
+@posts_bp.route("/<int:post_id>", methods=["GET"])
+async def get_post(post_id: int):
+    async with get_session() as session:
+        item = await PostFeedService(session).get_post(post_id)
+    if item is None:
+        return _bad("not_found", status=404, detail=f"post id={post_id}")
+    return jsonify(item)