feat: add inputs parameter to MCP tool invocation methods

[zinodynn]

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Summary

• feat: Forward chat input variables to MCP server via _meta

  • Enables passing additional variables from chat request inputs to MCP servers, facilitating use cases like identity verification and permission control.

• feat: Support MCP protocol-reserved _meta parameter in tool invocations

  • Adds the _meta field to CallToolRequestParams to comply with the MCP specification, enabling transmission of metadata such as progressToken or identityToken.

These changes improve flexibility for MCP-level business logic, allowing for more fine-grained control and context-aware processing based on upstream chat request details.

References:

• MCP Spec - General Fields
• #28076, #28167

Screenshots

Before	After
sql execution in MCP cannot be authenticated	The functions can be expanded by customizing parameters

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[gemini-code-assist]

Summary of Changes

Hello @zinodynn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the functionality of Multi-Chain Protocol (MCP) tools by allowing the forwarding of extra parameters, referred to as 'inputs,' from chat requests. This new capability provides a robust mechanism for implementing advanced business logic within MCPs, such as user authentication and fine-grained access control, by leveraging contextual information from the initial chat request. The change improves the overall adaptability and power of the tool invocation system.

Highlights

• Enhanced MCP Tool Invocation: Introduced the capability to pass additional inputs parameters from chat requests directly to Multi-Chain Protocol (MCP) tool invocation methods.
• Improved Flexibility: This change enables more flexible and context-aware processing within MCPs, supporting use cases like request-side identity verification and granular permission control.
• Conditional Input Passing: The inputs are conditionally passed to MCP tools, ensuring that only relevant tools receive these additional parameters, and are merged conservatively to avoid overwriting existing tool parameters.

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[gemini-code-assist]

Code Review

This pull request introduces an inputs parameter to the MCP tool invocation methods, enabling additional variables from chat requests to be passed to MCP servers. This is a valuable enhancement for implementing features like request-side identity verification and permission control. The changes are well-implemented, propagating the new parameter through the necessary layers from fc_agent_runner to ToolEngine and the base Tool class. The use of introspection in the base Tool to conditionally pass the inputs parameter is a good design choice for flexibility. I have identified one high-severity bug that could cause a runtime error and one medium-severity suggestion for improving exception handling. After addressing these points, the PR should be in great shape.

[zinodynn]

Reference my approach to pass input parameters from chat requests to MCP tools, as outlined below:

1. Create an identityToken using the app's input parameters, then save and publish it.

2. Modify the MCP server code, and receive the identityToken params:

export async function executeSqlToolHandler(
  { sql }: { sql: string }, 
  _extra: any // Additional parameters from chat request
) {
  const connector = ConnectorManager.getCurrentConnector();
  // Retrieve `input` params from the request via:
  // const identityToken = extra._meta?.identityToken;   <---  receive params
  try {
    // ... Use the `sql` parameter ...
  }
  // ...
}

3. Send a chat request (example curl command):

curl --location 'http://localhost:5001/v1/chat-messages' \
--header 'Authorization: Bearer app-xxxxxx' \
--header 'Content-Type: application/json' \
--data '{
    "inputs": {"identityToken":"eyJhbG...."},
    "query": "Query today'\''s sales orders?",
    "response_mode": "streaming",
    "user": "abc-123"
}'

[zinodynn]

@Nov1c444, to prevent every MCP from receiving the parameters, would it be a good idea to distinguish parameters in inputs using dot-separated notation (e.g., .)? For example, create a parameter like mysql-mcp-server.identityToken in inputs to pass it specifically to the mysql-mcp-server MCP. This way, other MCPs won’t receive the identityToken parameter. If this makes sense, I’ll proceed to work on it.