Refactor: O(1) lookup table for CRYPT_FIELDS in per-record encryption

Add CRYPT_FIELDS_BY_MODEL to CryptMixin, derived from CRYPT_FIELDS at
class definition time. _encrypt_record_inline() now does a single dict
lookup instead of a linear scan per record, eliminating the loop and
break pattern.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/documents/management/commands/document_exporter.py

@@ -605,15 +605,13 @@ class Command(CryptMixin, BaseCommand):
         """Encrypt sensitive fields in a single record, if passphrase is set."""
         if not self.passphrase:
             return
-        model = record.get("model", "")
-        for cfg in self.CRYPT_FIELDS:
-            if model == cfg["model_name"]:
-                for field in cfg["fields"]:
-                    if record["fields"].get(field):
-                        record["fields"][field] = self.encrypt_string(
-                            value=record["fields"][field],
-                        )
-                break
+        fields = self.CRYPT_FIELDS_BY_MODEL.get(record.get("model", ""))
+        if fields:
+            for field in fields:
+                if record["fields"].get(field):
+                    record["fields"][field] = self.encrypt_string(
+                        value=record["fields"][field],
+                    )
 
     def _write_split_manifest(
         self,

src/documents/management/commands/mixins.py

@@ -89,6 +89,10 @@ class CryptMixin:
             ],
         },
     ]
+    # O(1) lookup for per-record encryption; derived from CRYPT_FIELDS at class definition time
+    CRYPT_FIELDS_BY_MODEL: dict[str, list[str]] = {
+        cfg["model_name"]: cfg["fields"] for cfg in CRYPT_FIELDS
+    }
 
     def get_crypt_params(self) -> dict[str, dict[str, str | int]]:
         return {