Improve MCP Extension Support

[ahmedmuhsin]

This pull request introduces support for MCP (Model Context Protocol) annotations in Azure Functions and refactors binding name handling to improve consistency and validation. The most significant changes are the addition of MCP-related binding types and annotation processing, centralization of system-reserved binding name logic, and stricter validation for user-defined binding names.

MCP Annotation Support

• Added new MCP binding types (McpToolTrigger, McpToolProperty) to the BindingEnum and their corresponding annotation constants in AzureFunctionsAnnotationConstants.java. [1] [2]
• Implemented McpAnnotationProcessor.java, which processes MCP annotations by patching trigger and property bindings, aggregates tool properties, and ensures correct function.json generation.
• Integrated MCP annotation processing into the function configuration generation flow in AnnotationHandlerImpl.java.

Binding Name Handling and Validation

• Centralized the definition of the system-reserved binding name ($return) in AzureFunctionsAnnotationConstants.java and updated all usages to reference this constant instead of hardcoding the string. [1] [2] [3] [4] [5] [6] [7] [8] [9]
• Added validation logic in AnnotationHandlerImpl.java to ensure all user-defined binding names within a function are unique, while allowing duplicates for system-reserved names like $return.

Dependency Update

• Updated the Maven plugin version in azure-functions-maven-plugin/pom.xml from 1.39.0 to 1.40.0.

[Flanker32]

LGTM

[Flanker32]

@ahmedmuhsin Thanks for your efforts, the PR look fine.

One more question about the template, shall we add a return value to the function so that it could return something to mcp clients? Currently the void function will return empty to mcp clients, while usually mcp tools should return some messages.

[Flanker32]

LGTM

[Flanker32]

LGTM