fix(ui): isolate canvas design and interaction fixes

backend/app/api/v1/connections.py

@@ -5,11 +5,11 @@
 
 from app.api.deps import get_current_workspace_id, get_optional_user
 from app.core.database import get_db
-from app.schemas.connection import ConnectionCreate, ConnectionResponse, ConnectionUpdate
 from app.realtime.manager import (
     fire_and_forget_publish,
     fire_and_forget_publish_diagram,
 )
+from app.schemas.connection import ConnectionCreate, ConnectionResponse, ConnectionUpdate
 from app.services import connection_service, diagram_service, object_service
 from app.services.webhook_service import fire_and_forget_emit
 
@@ -84,8 +84,9 @@ async def create_connection(
         from_diagram_id=data.from_diagram_id,
         from_draft_id=data.from_draft_id,
     )
+    body = ConnectionResponse.model_validate(conn).model_dump(mode="json")
+    await db.commit()
     if draft_id is None:
-        body = ConnectionResponse.model_validate(conn).model_dump(mode="json")
         fire_and_forget_emit("connection.created", body)
         fire_and_forget_publish(
             getattr(source, "workspace_id", None),
@@ -115,8 +116,9 @@ async def update_connection(
         from_diagram_id=data.from_diagram_id,
         from_draft_id=data.from_draft_id,
     )
+    body = ConnectionResponse.model_validate(conn).model_dump(mode="json")
+    await db.commit()
     if conn.draft_id is None:
-        body = ConnectionResponse.model_validate(conn).model_dump(mode="json")
         fire_and_forget_emit("connection.updated", body)
         src = await object_service.get_object(db, conn.source_id)
         fire_and_forget_publish(
@@ -148,8 +150,9 @@ async def flip_connection(
         from_diagram_id=from_diagram_id,
         from_draft_id=from_draft_id,
     )
+    body = ConnectionResponse.model_validate(conn).model_dump(mode="json")
+    await db.commit()
     if conn.draft_id is None:
-        body = ConnectionResponse.model_validate(conn).model_dump(mode="json")
         fire_and_forget_emit("connection.updated", body)
         src = await object_service.get_object(db, conn.source_id)
         fire_and_forget_publish(
@@ -187,6 +190,7 @@ async def delete_connection(
         from_diagram_id=from_diagram_id,
         from_draft_id=from_draft_id,
     )
+    await db.commit()
     if not was_draft:
         fire_and_forget_emit("connection.deleted", {"id": conn_id_str})
         fire_and_forget_publish(src_ws_id, "connection.deleted", {"id": conn_id_str})

backend/app/api/v1/diagrams.py

@@ -4,7 +4,12 @@
 from pydantic import BaseModel
 from sqlalchemy.ext.asyncio import AsyncSession
 
+from app.api.deps import get_current_workspace_id, get_optional_user
 from app.core.database import get_db
+from app.realtime.manager import (
+    fire_and_forget_publish,
+    fire_and_forget_publish_diagram,
+)
 from app.schemas.diagram import (
     DiagramCreate,
     DiagramObjectCreate,
@@ -13,13 +18,13 @@
     DiagramResponse,
     DiagramUpdate,
 )
-from app.api.deps import get_current_workspace_id, get_optional_user
-from app.realtime.manager import (
-    fire_and_forget_publish,
-    fire_and_forget_publish_diagram,
+from app.services import (
+    access_service,
+    diagram_service,
+    draft_service,
+    pack_service,
+    workspace_service,
 )
-from app.services import access_service, diagram_service, draft_service, workspace_service
-from app.services import pack_service
 from app.services.webhook_service import fire_and_forget_emit
 
 router = APIRouter(prefix="/diagrams", tags=["diagrams"])
@@ -177,14 +182,18 @@ async def add_object_to_diagram(
     diagram = await diagram_service.get_diagram(db, diagram_id)
     if not diagram:
         raise HTTPException(status_code=404, detail="Diagram not found")
-    obj = await diagram_service.add_object_to_diagram(
-        db, diagram_id, data,
-        actor_user=current_user,
-        workspace_id=getattr(diagram, "workspace_id", None),
-        from_draft_id=data.from_draft_id,
-    )
+    try:
+        obj = await diagram_service.add_object_to_diagram(
+            db, diagram_id, data,
+            actor_user=current_user,
+            workspace_id=getattr(diagram, "workspace_id", None),
+            from_draft_id=data.from_draft_id,
+        )
+    except diagram_service.DiagramObjectTargetMissingError as exc:
+        raise HTTPException(status_code=404, detail="Object not found") from exc
     body = DiagramObjectResponse.model_validate(obj).model_dump(mode="json")
     payload = {"diagram_id": str(diagram_id), "diagram_object": body}
+    await db.commit()
     fire_and_forget_publish(
         getattr(diagram, "workspace_id", None),
         "diagram_object.added",
@@ -219,6 +228,7 @@ async def update_diagram_object(
         )
     body = DiagramObjectResponse.model_validate(obj).model_dump(mode="json")
     payload = {"diagram_id": str(diagram_id), "diagram_object": body}
+    await db.commit()
     fire_and_forget_publish(
         getattr(diagram, "workspace_id", None) if diagram else None,
         "diagram_object.updated",
@@ -249,6 +259,7 @@ async def remove_object_from_diagram(
             status_code=404, detail="Object not found in diagram"
         )
     payload = {"diagram_id": str(diagram_id), "object_id": str(object_id)}
+    await db.commit()
     fire_and_forget_publish(
         getattr(diagram, "workspace_id", None) if diagram else None,
         "diagram_object.removed",

backend/app/api/v1/objects.py

@@ -123,6 +123,7 @@ async def create_object(
             detail={"error": "invalid_repo_url", "message": str(exc)},
         ) from exc
     response = ObjectResponse.from_model(obj)
+    await db.commit()
     if draft_id is None:
         body = response.model_dump(mode="json")
         fire_and_forget_emit("object.created", body)

backend/app/services/diagram_service.py

@@ -6,6 +6,7 @@
 
 from app.models.connection import Connection
 from app.models.diagram import Diagram, DiagramObject
+from app.models.object import ModelObject
 from app.models.technology import Technology
 from app.schemas.diagram import (
     DiagramCreate,
@@ -140,6 +141,11 @@ async def delete_diagram(db: AsyncSession, diagram: Diagram) -> None:
 
 # ─── Diagram Objects (positions) ──────────────────────────
 
+
+class DiagramObjectTargetMissingError(ValueError):
+    """The object being placed on a diagram does not exist."""
+
+
 async def get_diagram_objects(
     db: AsyncSession, diagram_id: uuid.UUID
 ) -> list[DiagramObject]:
@@ -170,6 +176,10 @@ async def add_object_to_diagram(
     workspace_id: uuid.UUID | None = None,
     from_draft_id: uuid.UUID | None = None,
 ) -> DiagramObject:
+    target = await db.get(ModelObject, data.object_id)
+    if target is None:
+        raise DiagramObjectTargetMissingError(str(data.object_id))
+
     obj = DiagramObject(
         diagram_id=diagram_id,
         object_id=data.object_id,
@@ -199,7 +209,7 @@ async def add_object_to_diagram(
             target_type=UndoTargetType.DIAGRAM_OBJECT,
             target_id=obj.id,
             action=UndoAction.CREATE,
-            forward_summary=f"Added object to diagram"[:80],
+            forward_summary="Added object to diagram"[:80],
             inverse_payload={"target_id": str(obj.id)},
             after_state=activity_service.snapshot(obj, include_metadata=True),
             coalesce_key=f"diagram_object:{obj.id}:create",
@@ -263,7 +273,7 @@ async def update_diagram_object(
                     target_type=UndoTargetType.DIAGRAM_OBJECT,
                     target_id=obj.id,
                     action=UndoAction.UPDATE,
-                    forward_summary=f"Moved object in diagram"[:80],
+                    forward_summary="Moved object in diagram"[:80],
                     inverse_payload={"before": {k: v["before"] for k, v in pos_diff.items()}},
                     after_state={k: v["after"] for k, v in pos_diff.items()},
                     coalesce_key=f"diagram_object:{obj.id}:position",
@@ -280,7 +290,7 @@ async def update_diagram_object(
                     target_type=UndoTargetType.DIAGRAM_OBJECT,
                     target_id=obj.id,
                     action=UndoAction.UPDATE,
-                    forward_summary=f"Resized object in diagram"[:80],
+                    forward_summary="Resized object in diagram"[:80],
                     inverse_payload={"before": {k: v["before"] for k, v in size_diff.items()}},
                     after_state={k: v["after"] for k, v in size_diff.items()},
                     coalesce_key=f"diagram_object:{obj.id}:size",
@@ -298,7 +308,7 @@ async def update_diagram_object(
                     target_type=UndoTargetType.DIAGRAM_OBJECT,
                     target_id=obj.id,
                     action=UndoAction.UPDATE,
-                    forward_summary=f"Updated diagram object"[:80],
+                    forward_summary="Updated diagram object"[:80],
                     inverse_payload={"before": {k: v["before"] for k, v in other_diff.items()}},
                     after_state={k: v["after"] for k, v in other_diff.items()},
                     coalesce_key=f"diagram_object:{obj.id}:{','.join(sorted(other_diff.keys()))}",
@@ -351,7 +361,7 @@ async def remove_object_from_diagram(
             target_type=UndoTargetType.DIAGRAM_OBJECT,
             target_id=do_id,
             action=UndoAction.DELETE,
-            forward_summary=f"Removed object from diagram"[:80],
+            forward_summary="Removed object from diagram"[:80],
             inverse_payload={"snapshot": snapshot, "id": str(do_id)},
             after_state=None,
             coalesce_key=f"diagram_object:{do_id}:delete",