Release v0.4.0

[topherbullock]

Release v0.4.0

Summary

This PR prepares the v0.4.0 release of the MCP Ruby SDK, updating the version and documenting all changes since v0.3.0.

Release Notes

Added

• Client resources support with resources/list and resources/read methods (add resources/list and resources/read support to client #160)
• _meta field support for Tool schema (Add support for _meta field on tool schema #124)
• _meta field support for Prompt
• title field support for prompt arguments
• call_tool_raw method to client for accessing full tool responses ([client] Change call_tool method to return the full tool response to help get structuredContent #149)
• Structured content support in tool responses (Support structuredContent in tool response #147)
• AGENTS.md development guidance documentation (Add AGENTS.md with comprehensive development guidance #134)
• Dependabot configuration for automated dependency updates (Enable Dependabot #138)

Changed

• Set default content to empty array instead of nil (Set default content to an empty array instead of nil #150)
• Improved prompt spec compliance (fix Prompt type gaps with 2025-06-18 spec  #153)
• Allow output schema to be array of objects (Allow output schema to be array of objects #144)
• Return 202 response code for accepted JSON-RPC notifications (Fix to return a response code 202 if the server accepts JSON-RPC notifications and responses #114)
• Added validation to MCP::Configuration setters (Add validation to MCP::Configuration setters #145)
• Updated metaschema URI format for cross-OS compatibility

Fixed

• Client tools functionality and test coverage (Fix and add test for client tools functionality #166)
• Client resources test for empty responses (Fix test for empty resources response of client #162)
• Documentation typos and incorrect examples ([Doc] Fix incorrect example code in README #157, Fix some typos #146)
• Removed redundant transport requires (Remove unnecessary transport requires #154)
• Cleaned up unused block parameters and magic comments

[koic]

Looks good to me!