fix: Terminate sync immediately when project is deleted

src/basic_memory/repository/entity_repository.py

@@ -135,7 +135,20 @@ async def upsert_entity(self, entity: Entity) -> Entity:
                     )
                 return found
 
-            except IntegrityError:
+            except IntegrityError as e:
+                # Check if this is a FOREIGN KEY constraint failure
+                error_str = str(e)
+                if "FOREIGN KEY constraint failed" in error_str:
+                    # Import locally to avoid circular dependency (repository -> services -> repository)
+                    from basic_memory.services.exceptions import SyncFatalError
+
+                    # Project doesn't exist in database - this is a fatal sync error
+                    raise SyncFatalError(
+                        f"Cannot sync file '{entity.file_path}': "
+                        f"project_id={entity.project_id} does not exist in database. "
+                        f"The project may have been deleted. This sync will be terminated."
+                    ) from e
+
                 await session.rollback()
 
                 # Re-query after rollback to get a fresh, attached entity

src/basic_memory/services/exceptions.py

@@ -20,3 +20,18 @@ class DirectoryOperationError(Exception):
     """Raised when directory operations fail"""
 
     pass
+
+
+class SyncFatalError(Exception):
+    """Raised when sync encounters a fatal error that prevents continuation.
+
+    Fatal errors include:
+    - Project deleted during sync (FOREIGN KEY constraint)
+    - Database corruption
+    - Critical system failures
+
+    When this exception is raised, the entire sync operation should be terminated
+    immediately rather than attempting to continue with remaining files.
+    """
+
+    pass

src/basic_memory/sync/sync_service.py

@@ -22,6 +22,7 @@
 from basic_memory.repository import EntityRepository, RelationRepository, ObservationRepository
 from basic_memory.repository.search_repository import SearchRepository
 from basic_memory.services import EntityService, FileService
+from basic_memory.services.exceptions import SyncFatalError
 from basic_memory.services.link_resolver import LinkResolver
 from basic_memory.services.search_service import SearchService
 from basic_memory.services.sync_status_service import sync_status_tracker, SyncStatus
@@ -514,6 +515,13 @@ async def sync_file(
             return entity, checksum
 
         except Exception as e:
+            # Check if this is a fatal error (or caused by one)
+            # Fatal errors like project deletion should terminate sync immediately
+            if isinstance(e, SyncFatalError) or isinstance(e.__cause__, SyncFatalError):
+                logger.error(f"Fatal sync error encountered, terminating sync: path={path}")
+                raise
+
+            # Otherwise treat as recoverable file-level error
             error_msg = str(e)
             logger.error(f"Failed to sync file: path={path}, error={error_msg}")
 

tests/repository/test_entity_repository_upsert.py

@@ -6,6 +6,7 @@
 from basic_memory.models.knowledge import Entity
 from basic_memory.repository.entity_repository import EntityRepository
 from basic_memory.repository.project_repository import ProjectRepository
+from basic_memory.services.exceptions import SyncFatalError
 
 
 @pytest.mark.asyncio
@@ -436,3 +437,32 @@ async def test_upsert_entity_permalink_conflict_within_project_only(session_make
     assert result1.project_id == project1.id
     assert result2.project_id == project2.id
     assert result3.project_id == project1.id
+
+
+@pytest.mark.asyncio
+async def test_upsert_entity_with_invalid_project_id(entity_repository: EntityRepository):
+    """Test that upserting with non-existent project_id raises clear error.
+
+    This tests the fix for issue #188 where sync fails with FOREIGN KEY constraint
+    violations when a project is deleted during sync operations.
+    """
+    # Create entity with non-existent project_id
+    entity = Entity(
+        title="Test Entity",
+        entity_type="note",
+        file_path="test.md",
+        permalink="test",
+        project_id=99999,  # This project doesn't exist
+        content_type="text/markdown",
+        created_at=datetime.now(timezone.utc),
+        updated_at=datetime.now(timezone.utc),
+    )
+
+    # Should raise SyncFatalError with clear message about missing project
+    with pytest.raises(SyncFatalError) as exc_info:
+        await entity_repository.upsert_entity(entity)
+
+    error_msg = str(exc_info.value)
+    assert "project_id=99999 does not exist" in error_msg
+    assert "project may have been deleted" in error_msg.lower()
+    assert "sync will be terminated" in error_msg.lower()

tests/sync/test_sync_service.py

@@ -1565,3 +1565,79 @@ async def mock_compute_checksum(path):
         failure_info = sync_service._file_failures["checksum_fail.md"]
         assert failure_info.count == 1
         assert failure_info.last_checksum == ""  # Empty when checksum fails
+
+
+@pytest.mark.asyncio
+async def test_sync_fatal_error_terminates_sync_immediately(
+    sync_service: SyncService, project_config: ProjectConfig, entity_service: EntityService
+):
+    """Test that SyncFatalError terminates sync immediately without circuit breaker retry.
+
+    This tests the fix for issue #188 where project deletion during sync should
+    terminate immediately rather than retrying each file 3 times.
+    """
+    from unittest.mock import patch
+    from basic_memory.services.exceptions import SyncFatalError
+
+    project_dir = project_config.home
+
+    # Create multiple test files
+    await create_test_file(
+        project_dir / "file1.md",
+        dedent(
+            """
+            ---
+            type: knowledge
+            ---
+            # File 1
+            Content 1
+            """
+        ),
+    )
+    await create_test_file(
+        project_dir / "file2.md",
+        dedent(
+            """
+            ---
+            type: knowledge
+            ---
+            # File 2
+            Content 2
+            """
+        ),
+    )
+    await create_test_file(
+        project_dir / "file3.md",
+        dedent(
+            """
+            ---
+            type: knowledge
+            ---
+            # File 3
+            Content 3
+            """
+        ),
+    )
+
+    # Mock entity_service.create_entity_from_markdown to raise SyncFatalError on first file
+    # This simulates project being deleted during sync
+    async def mock_create_entity_from_markdown(*args, **kwargs):
+        raise SyncFatalError(
+            "Cannot sync file 'file1.md': project_id=99999 does not exist in database. "
+            "The project may have been deleted. This sync will be terminated."
+        )
+
+    with patch.object(
+        entity_service, "create_entity_from_markdown", side_effect=mock_create_entity_from_markdown
+    ):
+        # Sync should raise SyncFatalError and terminate immediately
+        with pytest.raises(SyncFatalError, match="project_id=99999 does not exist"):
+            await sync_service.sync(project_dir)
+
+    # Verify that circuit breaker did NOT record this as a file-level failure
+    # (SyncFatalError should bypass circuit breaker and re-raise immediately)
+    assert "file1.md" not in sync_service._file_failures
+
+    # Verify that no other files were attempted (sync terminated on first error)
+    # If circuit breaker was used, we'd see file1 in failures
+    # If sync continued, we'd see attempts for file2 and file3