feat(permissions): ABAC integration, principals caching, cache version validation

- Integrate ABAC policies into apply_visibility_filter() (allow/deny with priority)
- Add field whitelist (ABAC_ALLOWED_FIELDS) for build_sql_condition() security
- Add request-level ContextVar for user principals (group_ids, role_id)
- Set principals in deps.py (session + bearer auth)
- Use ContextVar in visibility.py and permission_resolver.py (N+1 fix)
- Add version validation to get_cached_visible_ids() (cache strategy unification)
- Deactivate delegation route (parked — not integrated into resolve_permissions)
- Add 7 ABAC integration tests

All 70 tests pass (7 ABAC + 63 existing). No regressions.

app/services/policy_service.py

@@ -30,6 +30,21 @@ _SUPPORTED_OPS = {
     "contains", "starts_with", "is_null", "is_not_null",
 }
 
+# ─── ABAC Field Whitelist ──────────────────────────────────────────
+# Only these fields may be referenced in policy conditions per entity
+# type. Prevents policies from filtering on sensitive columns such as
+# tenant_id, password_hash, etc.
+ABAC_ALLOWED_FIELDS: dict[str, set[str]] = {
+    "contact": {"status", "type", "country", "tags", "created_at", "updated_at", "owner_id"},
+    "file": {"status", "size", "mime_type", "created_at"},
+    "task": {"status", "priority", "due_date", "created_at"},
+    "calendar_event": {"status", "start_time", "end_time", "created_at"},
+    "mailbox": {"status", "created_at"},
+    "address": {"country", "city", "created_at", "updated_at"},
+    "contact_folder": {"name", "created_at"},
+    "workflow": {"status", "created_at"},
+}
+
 
 def _serialize_policy(p: EntityPolicy) -> dict:
     return {
@@ -51,6 +66,7 @@ def _serialize_policy(p: EntityPolicy) -> dict:
 def build_sql_condition(
     conditions: dict[str, Any],
     model: type,
+    entity_type: str | None = None,
 ) -> Any:
     """Recursively translate a JSONB conditions block into a SQLAlchemy filter expression.
 
@@ -65,6 +81,11 @@ def build_sql_condition(
     }
 
     Nested conditions are supported via rules that contain a nested conditions block.
+
+    When *entity_type* is provided, each rule's ``field`` is validated against
+    the ABAC_ALLOWED_FIELDS whitelist for that entity type. Unknown fields are
+    logged and skipped (not crashed) to prevent policies from filtering on
+    sensitive columns such as ``tenant_id`` or ``password_hash``.
     """
     if not conditions or "operator" not in conditions or "rules" not in conditions:
         return None
@@ -80,7 +101,7 @@ def build_sql_condition(
     for rule in rules:
         # Nested conditions block
         if "operator" in rule and "rules" in rule:
-            nested = build_sql_condition(rule, model)
+            nested = build_sql_condition(rule, model, entity_type=entity_type)
             if nested is not None:
                 clauses.append(nested)
             continue
@@ -96,6 +117,17 @@ def build_sql_condition(
             logger.warning(f"Unsupported condition operator: {op}")
             continue
 
+        # ── Field whitelist check ──────────────────────────────────
+        # Prevent policies from filtering on sensitive columns
+        if entity_type is not None:
+            allowed = ABAC_ALLOWED_FIELDS.get(entity_type)
+            if allowed is not None and field_name not in allowed:
+                logger.warning(
+                    f"ABAC field '{field_name}' not in whitelist for "
+                    f"entity_type '{entity_type}' — skipping rule"
+                )
+                continue
+
         # Get the model attribute
         attr: InstrumentedAttribute | None = getattr(model, field_name, None)
         if attr is None:
@@ -292,7 +324,7 @@ async def apply_policy_filter(
                 deny_clauses.append(True)
             continue
 
-        condition = build_sql_condition(policy.conditions, model)
+        condition = build_sql_condition(policy.conditions, model, entity_type=entity_type)
         if condition is None:
             continue