fix: move MCP SDK to peer dependencies

[agcty]

Summary

Move @modelcontextprotocol/sdk from direct dependencies to peer dependencies, allowing consumers to control their own MCP SDK version.

Problem

Currently, @modelcontextprotocol/sdk is pinned as a direct dependency ("^1.23.0"). This causes issues for consumers using different MCP SDK versions:

• Duplicate packages get installed
• Type mismatches when consumers reference MCP types (Tool, Prompt, Resource, ServerCapabilities) from their own code
• The agents package exposes MCP SDK types in its public API (e.g., MCPServersState, McpAgent.server)

Solution

• @modelcontextprotocol/sdk: required peer dep (>=1.0.0)

Unlike the AI SDK packages where some are optional, MCP is a required peer dependency because:

1. MCP functionality is core to the package (every Agent has this.mcp built-in)
2. Types like MCPServersState and McpAgent are fundamental exports
3. The McpAgent abstract class directly exposes McpServer | Server types

Breaking Changes

Consumers who don't already have @modelcontextprotocol/sdk installed will need to add it explicitly. However, anyone using MCP features is likely already interacting with MCP types.

Related to #42

🤖 Generated with Claude Code

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commit: 1c2efb4

[whoiskatrin]

@agcty don't merge it just yet, please

[threepointone]

because the mcp sdk does breaking changes in minors right now, I don't think we can actually guarantee this. not a great situation for us to be in unfortunately. we need to think through this.

tagging @mattzcarey for visibility

[threepointone]

blocking this while we figure out what to do here