perf(provenance): optimize lineage integrity checks and clean up top-level imports (#792)

- Reuse lineage['integrity_verified'] in _build_provenance in O(1) time when available, eliminating redundant SHA-256 verification loops across lineage chains.

- Improve compute_checksum dictionary handling in semantica/provenance/integrity.py so None values fall back cleanly to ProvenanceEntry defaults.

- Move json and verify_checksum imports to module top-level in semantica/provenance/manager.py to avoid function-local import overhead during get_lineage calls.

semantica/explorer/routes/provenance.py

@@ -144,8 +144,11 @@ def _build_provenance(session: GraphSession, node_id: Optional[str] = None) -> d
         if manager is not None:
             lineage = manager.get_lineage(node_id)
             if lineage and lineage.get("entity_count", 0) > 0:
-                entries = lineage.get("lineage_chain") or lineage.get("entries") or []
-                if all(verify_checksum(entry) for entry in entries):
+                integrity_ok = lineage.get("integrity_verified")
+                if integrity_ok is None:
+                    entries = lineage.get("lineage_chain") or lineage.get("entries") or []
+                    integrity_ok = all(verify_checksum(entry) for entry in entries)
+                if integrity_ok:
                     return _transform_audit_lineage(lineage, node_id)
                 logger.warning(
                     f"Provenance integrity verification failed for {node_id}, falling back to graph traversal"

semantica/provenance/integrity.py

@@ -51,12 +51,12 @@ def compute_checksum(entry: Any) -> str:
     # Concatenate critical fields for checksum
     if isinstance(entry, dict):
         data = (
-            f"{entry.get('entity_id', '')}"
-            f"{entry.get('entity_type', '')}"
-            f"{entry.get('activity_id', '')}"
-            f"{entry.get('source_document', '')}"
-            f"{entry.get('timestamp', '')}"
-            f"{entry.get('confidence', 1.0)}"
+            f"{entry.get('entity_id') or ''}"
+            f"{entry.get('entity_type') or ''}"
+            f"{entry.get('activity_id') or ''}"
+            f"{entry.get('source_document') or ''}"
+            f"{entry.get('timestamp') or ''}"
+            f"{entry.get('confidence') if entry.get('confidence') is not None else 1.0}"
         )
     else:
         data = (

semantica/provenance/manager.py

@@ -29,11 +29,12 @@ from collections.abc import Mapping
 from datetime import datetime
 from contextlib import contextmanager
 import copy
+import json
 import threading
 
 from .schemas import ProvenanceEntry, SourceReference
 from .storage import ProvenanceStorage, InMemoryStorage, SQLiteStorage
-from .integrity import compute_checksum
+from .integrity import compute_checksum, verify_checksum
 
 
 @contextmanager
@@ -553,7 +554,6 @@ class ProvenanceManager:
                 meta = entry.metadata
                 if isinstance(meta, str):
                     try:
-                        import json
                         meta = json.loads(meta)
                     except (json.JSONDecodeError, TypeError):
                         pass
@@ -561,7 +561,6 @@ class ProvenanceManager:
                 if isinstance(meta, dict):
                     aggregated_metadata.update(meta)
         
-        from .integrity import verify_checksum
         integrity_verified = all(verify_checksum(entry) for entry in lineage_entries)
         chain_dicts = [entry.to_dict() for entry in lineage_entries]
         return {