diff --git a/src/langbot/pkg/api/application/tool_grants.py b/src/langbot/pkg/api/application/tool_grants.py
index a99cbf734..0fb7c2fed 100644
--- a/src/langbot/pkg/api/application/tool_grants.py
+++ b/src/langbot/pkg/api/application/tool_grants.py
@@ -10,6 +10,11 @@ from .contracts import ApplicationAPIError, ApplicationAPIException, Operation
 from .operation_docs import DOMAINS, get_operation_doc
 
 
+def _is_processor(context: Any) -> bool:
+    principal = getattr(context, 'principal', None)
+    return getattr(principal, 'principal_type', None) == PrincipalType.PROCESSOR
+
+
 def validate_grant_change(
     ap: Any,
     editor_context: RequestContext,
@@ -66,6 +71,18 @@ def validate_grant_change(
     if not added_ids:
         return normalized_new
 
+    # Granting is a human authorization act. A processor that can update processor
+    # configuration must not widen any processor's grants, including its own.
+    if _is_processor(editor_context):
+        raise ApplicationAPIException(
+            ApplicationAPIError(
+                code='permission_denied',
+                message=f'Processors cannot grant workspace operations: {added_ids}',
+                status_code=403,
+                details={'operations': added_ids, 'denied_operations': added_ids},
+            )
+        )
+
     app_api = getattr(ap, 'application_api', None)
     if app_api is None:
         from .api import ApplicationAPI
@@ -147,7 +164,7 @@ def get_workspace_operations_catalog(ap: Any, context: Any) -> dict[str, Any]:
         has_perm = (
             has_permission(context, spec.permission) if context is not None and hasattr(context, 'workspace') else False
         )
-        grantable = bool(can_run and has_perm)
+        grantable = bool(can_run and has_perm and not _is_processor(context))
 
         perm = spec.permission
         perm_str = perm.value if hasattr(perm, 'value') else str(perm)
diff --git a/tests/unit_tests/api/test_tool_grants.py b/tests/unit_tests/api/test_tool_grants.py
index deaadcab2..38436e519 100644
--- a/tests/unit_tests/api/test_tool_grants.py
+++ b/tests/unit_tests/api/test_tool_grants.py
@@ -249,3 +249,34 @@ def test_workspace_operations_catalog_and_grantable_flags(test_host):
     ]
     for op in viewer_view_ops:
         assert op['grantable'] is True
+
+
+# 8. A processor must not widen grants, even within its own derived permissions
+def test_processor_principal_cannot_add_grants(test_host):
+    import asyncio
+
+    from langbot.pkg.api.application.processor_context import build_processor_request_context
+
+    processor_ctx = asyncio.run(
+        build_processor_request_context(
+            test_host,
+            workspace_uuid='ws-1',
+            processor_kind='pipeline',
+            processor_uuid='pipe-1',
+            run_id='run-1',
+            operation_ids=['pipeline.extensions.update'],
+        )
+    )
+    old = ['pipeline.extensions.update']
+
+    with pytest.raises(ApplicationAPIException) as exc_info:
+        validate_grant_change(test_host, processor_ctx, old, [*old, 'bot.delete'])
+    assert exc_info.value.error.code == 'permission_denied'
+    assert exc_info.value.error.details['operations'] == ['bot.delete']
+
+    # Keeping or removing existing grants is still allowed.
+    assert validate_grant_change(test_host, processor_ctx, old, old) == old
+    assert validate_grant_change(test_host, processor_ctx, old, []) == []
+
+    catalog = get_workspace_operations_catalog(test_host, processor_ctx)
+    assert not any(op['grantable'] for op in catalog['workspace_operations'])