[BUG]: Tool invocation fails with Pydantic validation errors

[BenjaminNechicattu]

🐞 Bug Summary

Tool invocation fails with Pydantic validation errors when returning resource_link content.

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🧩 Affected Component

Select the area of the project impacted:

• mcpgateway - API
• mcpgateway - UI (admin panel)
• mcpgateway.wrapper - stdio wrapper
• Federation or Transports
• CLI, Makefiles, or shell scripts
• Container setup (Docker/Podman/Compose)
• Other (explain below)

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🔁 Steps to Reproduce

1. resiter a gateway with moody server https://screening-ai-services.npe.moodys.cloud/mcp
2. Invoke tool screenAndWait

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🤔 Expected Behavior

What should have happened instead?

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📓 Logs / Error Output

Paste any relevant stack traces or logs here.
⚠️ Do not paste secrets, credentials, or tokens.

2026-01-27T11:21:19 - httpcore.http11 - DEBUG - response_closed.started
2026-01-27T11:21:19 - httpcore.http11 - DEBUG - response_closed.complete
2026-01-27T11:21:19 - httpcore.connection - DEBUG - close.started
2026-01-27T11:21:19 - httpcore.connection - DEBUG - close.complete
2026-01-27T11:21:19 - mcpgateway.services.structured_logger - INFO - [tool_service] MCP tool call completed: screenAndWait
2026-01-27T11:21:19 - mcpgateway.services.structured_logger - ERROR - [tool_service] Tool 'sayujya-mcp-moody-jan-27-v3-screenandwait' invocation failed
2026-01-27T11:21:19 - mcpgateway.transports.streamablehttp_transport - ERROR - Error calling tool 'sayujya-mcp-moody-jan-27-v3-screenandwait': Tool invocation failed: 18 validation errors for CallToolResult
content.0.TextContent.type
  Input should be 'text' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.TextContent.text
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.0.ImageContent.type
  Input should be 'image' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.ImageContent.data
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.0.AudioContent.type
  Input should be 'audio' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.AudioContent.data
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.0.ResourceLink.uri
  Input should be a valid string [type=string_type, input_value=AnyUrl('file://moodys-legal-disclaimer/'), input_type=AnyUrl]
    For further information visit https://errors.pydantic.dev/2.12/v/string_type
content.0.EmbeddedResource.type
  Input should be 'resource' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.EmbeddedResource.resource
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.TextContent.type
  Input should be 'text' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.TextContent.text
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.ImageContent.type
  Input should be 'image' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.ImageContent.data
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.AudioContent.type
  Input should be 'audio' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.AudioContent.data
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.ResourceLink.uri
  Input should be a valid string [type=string_type, input_value=AnyUrl('grid-entities://8...b517-fd4e0e24997f.json'), input_type=AnyUrl]
    For further information visit https://errors.pydantic.dev/2.12/v/string_type
content.2.EmbeddedResource.type
  Input should be 'resource' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.EmbeddedResource.resource
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
Traceback (most recent call last):
  File "/Users/benjamin/Documents/Projects/ibm_projects/mcpgateway/mcp-context-forge/mcpgateway/services/tool_service.py", line 3202, in invoke_tool
    tool_result = ToolResult(content=filtered_response, structured_content=structured, is_error=is_err, meta=getattr(tool_call_result, "meta", None))
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/benjamin/Documents/Projects/ibm_projects/mcpgateway/mcp-context-forge/.venv/lib/python3.11/site-packages/pydantic/main.py", line 250, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.ValidationError: 18 validation errors for CallToolResult
content.0.TextContent.type
  Input should be 'text' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.TextContent.text
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.0.ImageContent.type
  Input should be 'image' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.ImageContent.data
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.0.AudioContent.type
  Input should be 'audio' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.AudioContent.data
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.0.ResourceLink.uri
  Input should be a valid string [type=string_type, input_value=AnyUrl('file://moodys-legal-disclaimer/'), input_type=AnyUrl]
    For further information visit https://errors.pydantic.dev/2.12/v/string_type
content.0.EmbeddedResource.type
  Input should be 'resource' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.EmbeddedResource.resource
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.TextContent.type
  Input should be 'text' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.TextContent.text
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.ImageContent.type
  Input should be 'image' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.ImageContent.data
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.AudioContent.type
  Input should be 'audio' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.AudioContent.data
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.ResourceLink.uri
  Input should be a valid string [type=string_type, input_value=AnyUrl('grid-entities://8...b517-fd4e0e24997f.json'), input_type=AnyUrl]
    For further information visit https://errors.pydantic.dev/2.12/v/string_type
content.2.EmbeddedResource.type
  Input should be 'resource' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.EmbeddedResource.resource
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/benjamin/Documents/Projects/ibm_projects/mcpgateway/mcp-context-forge/mcpgateway/transports/streamablehttp_transport.py", line 516, in call_tool
    result = await tool_service.invoke_tool(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/benjamin/Documents/Projects/ibm_projects/mcpgateway/mcp-context-forge/mcpgateway/services/tool_service.py", line 3246, in invoke_tool
    raise ToolInvocationError(f"Tool invocation failed: {error_message}")
mcpgateway.services.tool_service.ToolInvocationError: Tool invocation failed: 18 validation errors for CallToolResult
content.0.TextContent.type
  Input should be 'text' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.TextContent.text
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.0.ImageContent.type
  Input should be 'image' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.ImageContent.data
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.0.AudioContent.type
  Input should be 'audio' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.AudioContent.data
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.0.ResourceLink.uri
  Input should be a valid string [type=string_type, input_value=AnyUrl('file://moodys-legal-disclaimer/'), input_type=AnyUrl]
    For further information visit https://errors.pydantic.dev/2.12/v/string_type
content.0.EmbeddedResource.type
  Input should be 'resource' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.0.EmbeddedResource.resource
  Field required [type=missing, input_value={'name': 'Legal Disclaime...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.TextContent.type
  Input should be 'text' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.TextContent.text
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.ImageContent.type
  Input should be 'image' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.ImageContent.data
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.AudioContent.type
  Input should be 'audio' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.AudioContent.data
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
content.2.ResourceLink.uri
  Input should be a valid string [type=string_type, input_value=AnyUrl('grid-entities://8...b517-fd4e0e24997f.json'), input_type=AnyUrl]
    For further information visit https://errors.pydantic.dev/2.12/v/string_type
content.2.EmbeddedResource.type
  Input should be 'resource' [type=literal_error, input_value='resource_link', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/literal_error
content.2.EmbeddedResource.resource
  Field required [type=missing, input_value={'name': 'gridEntityGroun...'type': 'resource_link'}, input_type=dict]
    For further information visit https://errors.pydantic.dev/2.12/v/missing
2026-01-27T11:21:19 - mcp.server.lowlevel.server - DEBUG - Response sent
2026-01-27T11:21:19 - mcp.server.streamable_http - INFO - Terminating session: None
2026-01-27T11:21:19 - mcpgateway.plugins.auth_pre_check - INFO - [WXO_AUTH] Auth audit: POST /servers/09792051036f4725b5f1e3437fb0d5ce/mcp -> 200 (auth_present=True, client=127.0.0.1)
2026-01-27T11:21:19 - mcpgateway.services.structured_logger - INFO - [http_gateway] Request completed: POST /servers/09792051036f4725b5f1e3437fb0d5ce/mcp - 200

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🧠 Environment Info

You can retrieve most of this from the /version endpoint.

Key	Value
Version or commit	e.g. v0.9.0 or main@a1b2c3d
Runtime	e.g. Python 3.11, Gunicorn
Platform / OS	e.g. Ubuntu 22.04, macOS
Container	e.g. Docker, Podman, none

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🧩 Additional Context (optional)

Add any configuration details, flags, or related issues.

[kevalmahajan]

Root Cause Summary:

The tool invocation failed due to two issues:

1. Serialization Issue: The internal ToolResult model validation failed because AnyUrl objects (from the MCP SDK) were being passed directly to fields expecting strict str types.
2. Transport Assumption: The Streamable HTTP transport naive implementation assumed all tool outputs were TextContent, causing an AttributeError when a tool returned a ResourceLink (which has no text attribute).