fix(mcp): Handle optional credentials in graph save and execution validation

- _on_graph_activate: Clear stale credential references for optional
  fields instead of blocking the save. Checks both node metadata
  (credentials_optional) and block schema (field not in required_fields).
- _validate_node_input_credentials: Use block schema's required_fields
  as fallback for credentials_optional check, so MCP blocks with
  default={} credentials are properly treated as optional.
- Set credentials_optional metadata on new MCP nodes in the frontend.

autogpt_platform/backend/backend/executor/utils.py

@@ -265,7 +265,13 @@ async def _validate_node_input_credentials(
         # Track if any credential field is missing for this node
         has_missing_credentials = False
 
+        # A credential field is optional if the node metadata says so, or if
+        # the block schema declares a default for the field.
+        required_fields = block.input_schema.get_required_fields()
+        is_creds_optional = node.credentials_optional
+
         for field_name, credentials_meta_type in credentials_fields.items():
+            field_is_optional = is_creds_optional or field_name not in required_fields
             try:
                 # Check nodes_input_masks first, then input_default
                 field_value = None
@@ -278,7 +284,7 @@ async def _validate_node_input_credentials(
                 elif field_name in node.input_default:
                     # For optional credentials, don't use input_default - treat as missing
                     # This prevents stale credential IDs from failing validation
-                    if node.credentials_optional:
+                    if field_is_optional:
                         field_value = None
                     else:
                         field_value = node.input_default[field_name]
@@ -288,8 +294,8 @@ async def _validate_node_input_credentials(
                     isinstance(field_value, dict) and not field_value.get("id")
                 ):
                     has_missing_credentials = True
-                    # If node has credentials_optional flag, mark for skipping instead of error
-                    if node.credentials_optional:
+                    # If credential field is optional, skip instead of error
+                    if field_is_optional:
                         continue  # Don't add error, will be marked for skip after loop
                     else:
                         credential_errors[node.id][
@@ -343,7 +349,7 @@ async def _validate_node_input_credentials(
         # The executor will pass credentials=None to the block's run().
         if (
             has_missing_credentials
-            and node.credentials_optional
+            and is_creds_optional
             and node.id not in credential_errors
         ):
             logger.info(

autogpt_platform/backend/backend/integrations/webhooks/graph_lifecycle_hooks.py

@@ -50,6 +50,21 @@ async def _on_graph_activate(graph: "BaseGraph | GraphModel", user_id: str):
             if (
                 creds_meta := new_node.input_default.get(creds_field_name)
             ) and not await get_credentials(creds_meta["id"]):
+                # If the credential field is optional (has a default in the
+                # schema, or node metadata marks it optional), clear the stale
+                # reference instead of blocking the save.
+                creds_field_optional = (
+                    new_node.credentials_optional
+                    or creds_field_name not in block_input_schema.get_required_fields()
+                )
+                if creds_field_optional:
+                    new_node.input_default[creds_field_name] = {}
+                    logger.warning(
+                        f"Node #{new_node.id}: cleared stale optional "
+                        f"credentials #{creds_meta['id']} for "
+                        f"'{creds_field_name}'"
+                    )
+                    continue
                 raise ValueError(
                     f"Node #{new_node.id} input '{creds_field_name}' updated with "
                     f"non-existent credentials #{creds_meta['id']}"

autogpt_platform/frontend/src/app/(platform)/build/components/legacy-builder/Flow/Flow.tsx

@@ -748,6 +748,10 @@ const FlowEditor: React.FC<{
           block_id: blockID,
           isOutputStatic: nodeSchema.staticOutput,
           uiType: nodeSchema.uiType,
+          // MCP blocks have optional credentials (public servers don't need auth)
+          ...(blockID === SpecialBlockID.MCP_TOOL && {
+            metadata: { credentials_optional: true },
+          }),
         },
       };