diff --git a/api/controllers/service_api/app/annotation.py b/api/controllers/service_api/app/annotation.py
index ef254ca357..c22190cbc9 100644
--- a/api/controllers/service_api/app/annotation.py
+++ b/api/controllers/service_api/app/annotation.py
@@ -185,4 +185,4 @@ class AnnotationUpdateDeleteApi(Resource):
     def delete(self, app_model: App, annotation_id: str):
         """Delete an annotation."""
         AppAnnotationService.delete_app_annotation(app_model.id, annotation_id)
-        return {"result": "success"}, 204
+        return "", 204
diff --git a/api/controllers/service_api/app/conversation.py b/api/controllers/service_api/app/conversation.py
index 8e29c9ff0f..edbf011656 100644
--- a/api/controllers/service_api/app/conversation.py
+++ b/api/controllers/service_api/app/conversation.py
@@ -14,7 +14,6 @@ from controllers.service_api.wraps import FetchUserArg, WhereisUserArg, validate
 from core.app.entities.app_invoke_entities import InvokeFrom
 from extensions.ext_database import db
 from fields.conversation_fields import (
-    ConversationDelete,
     ConversationInfiniteScrollPagination,
     SimpleConversation,
 )
@@ -163,7 +162,7 @@ class ConversationDetailApi(Resource):
             ConversationService.delete(app_model, conversation_id, end_user)
         except services.errors.conversation.ConversationNotExistsError:
             raise NotFound("Conversation Not Exists.")
-        return ConversationDelete(result="success").model_dump(mode="json"), 204
+        return "", 204
 
 
 @service_api_ns.route("/conversations/<uuid:c_id>/name")
diff --git a/api/controllers/service_api/app/workflow.py b/api/controllers/service_api/app/workflow.py
index b2148f4fa1..35dd22c801 100644
--- a/api/controllers/service_api/app/workflow.py
+++ b/api/controllers/service_api/app/workflow.py
@@ -132,6 +132,8 @@ class WorkflowRunDetailApi(Resource):
             app_id=app_model.id,
             run_id=workflow_run_id,
         )
+        if not workflow_run:
+            raise NotFound("Workflow run not found.")
         return workflow_run
 
 
diff --git a/api/migrations/versions/2026_02_26_1336-e288952f2994_add_partial_indexes_on_conversations_.py b/api/migrations/versions/2026_02_26_1336-e288952f2994_add_partial_indexes_on_conversations_.py
new file mode 100644
index 0000000000..ed794178b3
--- /dev/null
+++ b/api/migrations/versions/2026_02_26_1336-e288952f2994_add_partial_indexes_on_conversations_.py
@@ -0,0 +1,37 @@
+"""add partial indexes on conversations for app_id with created_at and updated_at
+
+Revision ID: e288952f2994
+Revises: fce013ca180e
+Create Date: 2026-02-26 13:36:45.928922
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = 'e288952f2994'
+down_revision = 'fce013ca180e'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    with op.batch_alter_table('conversations', schema=None) as batch_op:
+        batch_op.create_index(
+            'conversation_app_created_at_idx',
+            ['app_id', sa.literal_column('created_at DESC')],
+            unique=False,
+            postgresql_where=sa.text('is_deleted IS false'),
+        )
+        batch_op.create_index(
+            'conversation_app_updated_at_idx',
+            ['app_id', sa.literal_column('updated_at DESC')],
+            unique=False,
+            postgresql_where=sa.text('is_deleted IS false'),
+        )
+
+
+def downgrade():
+    with op.batch_alter_table('conversations', schema=None) as batch_op:
+        batch_op.drop_index('conversation_app_updated_at_idx')
+        batch_op.drop_index('conversation_app_created_at_idx')
diff --git a/api/models/model.py b/api/models/model.py
index a5bca06666..2bf80edb80 100644
--- a/api/models/model.py
+++ b/api/models/model.py
@@ -711,6 +711,18 @@ class Conversation(Base):
     __table_args__ = (
         sa.PrimaryKeyConstraint("id", name="conversation_pkey"),
         sa.Index("conversation_app_from_user_idx", "app_id", "from_source", "from_end_user_id"),
+        sa.Index(
+            "conversation_app_created_at_idx",
+            "app_id",
+            sa.text("created_at DESC"),
+            postgresql_where=sa.text("is_deleted IS false"),
+        ),
+        sa.Index(
+            "conversation_app_updated_at_idx",
+            "app_id",
+            sa.text("updated_at DESC"),
+            postgresql_where=sa.text("is_deleted IS false"),
+        ),
     )
 
     id: Mapped[str] = mapped_column(StringUUID, default=lambda: str(uuid4()))