Add mcp search tool, lazy mcp load, reduce mcp tool occupying a lot of context

What feature would you like to see?

When MCP tool descriptions exceed 10% of the context window, they are automatically deferred and discovered via the MCPSearch tool instead of being loaded upfront. This reduces context usage for users with many MCP tools configured.

References:

• high level description: https://x.com/i/status/2011523109871108570
• tool search specification: https://platform.claude.com/docs/en/agents-and-tools/tool-use/tool-search-tool
• original Claude Code issue: https://github.com/anthropics/claude-code/issues/7336

Related issues:

• https://github.com/openai/codex/issues/2335

Additional information

_No response_