[FEATURE] VSCode: MCP tool calls should display parameters like built-in tools

Summary

In the VSCode extension, built-in tool calls display readable parameter summaries, but MCP tool calls show only an opaque reference. This makes it impossible for users to understand what an MCP tool is doing without expanding the output.

Built-in tool (readable):

● Grep "config" (in /Users/.../my-project, glob: "*.json")
  6 lines of output

MCP tool (opaque):

mcp__my-server__my_tool tool output (10gvlv)#28-30

Expected behavior

MCP tool calls should show their parameters in the same human-readable format as built-in tools. For example:

● my-mcp-server - fetch_data (id: "abc-123")
  3 lines of output

The tool name, server name, and key parameters are all available from the JSON-RPC call — they just aren't being rendered.

Why this matters

• Users can't tell what the AI is doing when it calls MCP tools
• Reduces trust — built-in tools are transparent, MCP tools are a black box
• This will slow MCP adoption since the experience feels second-class compared to built-in tools
• The terminal UI actually shows parameters (per #14684, sometimes too verbosely) — VSCode should too

Environment

• Claude Code VSCode extension
• macOS, custom MCP server via stdio transport