Multi-player sessions – support updating MCP server headers mid-session

We use the Claude Code SDK to run hosted agent sessions. At session creation, we pass MCP servers with Authorization headers via ClaudeAgentOptions.mcp_servers. We need to update those headers per-turn as different users send messages. Today, headers are set once and can't be changed for the lifetime of the session.

Use cases this would unlock

• Multi-player sessions – multiple users sharing a session, each with their own MCP server credentials per turn
• Long-lived sessions – sessions that outlive token expiry, with no recovery path today

What exists today

The SDK already supports mid-session MCP operations via control messages:

• mcp_reconnect – reconnect a failed server
• mcp_toggle – enable/disable a server

But there's no equivalent for updating headers on a running server.