Fix page creation labels and webhook race condition

- Updated shared submodule: page-aware blog_new template labels
- _upsert_post: handle concurrent webhook INSERTs via savepoint + retry

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bp/blog/ghost/ghost_sync.py

@@ -164,13 +164,8 @@ async def _upsert_tag(sess: AsyncSession, gt: Dict[str, Any]) -> Tag:
     return obj
 
 
-async def _upsert_post(sess: AsyncSession, gp: Dict[str, Any], author_map: Dict[str, Author], tag_map: Dict[str, Tag]) -> Post:
-    res = await sess.execute(select(Post).where(Post.ghost_id == gp["id"]))
-    obj = res.scalar_one_or_none()
-    if obj is None:
-        obj = Post(ghost_id=gp["id"])  # type: ignore[call-arg]
-        sess.add(obj)
-
+def _apply_ghost_fields(obj: Post, gp: Dict[str, Any], author_map: Dict[str, Author], tag_map: Dict[str, Tag]) -> None:
+    """Apply Ghost API fields to a Post ORM object."""
     obj.deleted_at = None  # revive if soft-deleted
 
     obj.uuid = gp.get("uuid") or obj.uuid
@@ -213,7 +208,29 @@ async def _upsert_post(sess: AsyncSession, gp: Dict[str, Any], author_map: Dict[
     pt = gp.get("primary_tag")
     obj.primary_tag_id = tag_map[pt["id"].strip()].id if (pt and pt["id"] in tag_map) else None  # type: ignore[index]
 
-    await sess.flush()
+
+async def _upsert_post(sess: AsyncSession, gp: Dict[str, Any], author_map: Dict[str, Author], tag_map: Dict[str, Tag]) -> Post:
+    from sqlalchemy.exc import IntegrityError
+
+    res = await sess.execute(select(Post).where(Post.ghost_id == gp["id"]))
+    obj = res.scalar_one_or_none()
+    if obj is None:
+        obj = Post(ghost_id=gp["id"])  # type: ignore[call-arg]
+        sess.add(obj)
+
+    _apply_ghost_fields(obj, gp, author_map, tag_map)
+
+    try:
+        async with sess.begin_nested():
+            await sess.flush()
+    except IntegrityError:
+        # Race condition: another request inserted this ghost_id concurrently.
+        # Expunge the failed object, re-select the existing row, and update it.
+        sess.expunge(obj)
+        res = await sess.execute(select(Post).where(Post.ghost_id == gp["id"]))
+        obj = res.scalar_one()
+        _apply_ghost_fields(obj, gp, author_map, tag_map)
+        await sess.flush()
 
     # Backfill user_id from primary author email if not already set
     if obj.user_id is None and obj.primary_author_id is not None: