perf(monitoring): load execution details on demand

- Load overview first and fetch secondary sections when expanded
- Add a covering index and select conversation IDs before loading page payloads
- Preserve full-detail API compatibility and add pagination and lazy-loading tests

tests/unit_tests/persistence/test_conversation_page_index.py

@@ -0,0 +1,42 @@
+"""Conversation paging index is safe for existing and fresh databases."""
+
+import importlib
+
+import sqlalchemy as sa
+from alembic.migration import MigrationContext
+from alembic.operations import Operations
+
+from langbot.pkg.entity.persistence.monitoring import MonitoringMessage
+
+
+def test_conversation_index_migration_preserves_history_and_matches_metadata():
+    migration = importlib.import_module('langbot.pkg.persistence.alembic.versions.0040_conversation_page_index')
+    engine = sa.create_engine('sqlite:///:memory:')
+    metadata = sa.MetaData()
+    table = sa.Table(
+        'monitoring_messages',
+        metadata,
+        *[
+            sa.Column(name, sa.String, primary_key=name == 'id')
+            for name in ('id', 'workspace_uuid', 'bot_id', 'session_id', 'timestamp', 'message_content')
+        ],
+    )
+    sa.Index('existing_index', table.c.workspace_uuid)
+    try:
+        with engine.begin() as connection:
+            metadata.create_all(connection)
+            connection.execute(table.insert().values(id='history', message_content='inline media'))
+            with Operations.context(MigrationContext.configure(connection)):
+                migration.upgrade()
+                migration.upgrade()
+                indexes = {
+                    index['name']: index['column_names'] for index in sa.inspect(connection).get_indexes(table.name)
+                }
+                expected = next(index for index in MonitoringMessage.__table__.indexes if index.name == migration.INDEX)
+                assert indexes[migration.INDEX] == [column.name for column in expected.columns]
+                migration.downgrade()
+                assert {index['name'] for index in sa.inspect(connection).get_indexes(table.name)} == {'existing_index'}
+                assert connection.scalar(sa.select(table.c.message_content)) == 'inline media'
+                migration.upgrade()
+    finally:
+        engine.dispose()