Client polish and consistency #269

Problem

The clients differ in small things that readers will copy: how they identify themselves, how they launch a server, and how they handle unusual input. None of this breaks the demo, but it makes the five examples look like five different programs.

Tasks

• Send explicit client info, mcp-client-<lang> / 1.0.0, from all five clients. Rust already does (Rust: negotiate 2026-07-28, call the Messages API directly, and bump rmcp to 3.4 #205). The others don't yet:
  • Python and Ruby pass nothing, so the SDK default is used.
  • Go sends version 0.1.0.
  • TypeScript sends the name mcp-client-cli.
• Skip empty input. Python and TypeScript currently send "" to the API and get a 400.
• Match quit after trimming whitespace and ignoring case, in every client. TypeScript doesn't trim.
• Print usage errors to stderr and exit with status 1, in every client. TypeScript exits 0, and Python and Ruby print to stdout.
• Run cleanup on Ctrl-C in Go, Rust and Ruby. In Ruby, rescue Interrupt, which isn't a StandardError. In Go, use signal.NotifyContext.
• Use one way to launch the server. My recommendation is command + args in all five clients, as Go and Rust already do. That matches the claim that the client "connects to any stdio server". It also avoids a trap in TypeScript and Ruby: they launch .py files with bare python3, which doesn't work for the uv-managed Python server. If the file-path form stays instead, map .py to uv --directory ... run everywhere and support the same set of extensions in every client.
• Add mcp-client-rust/.env.example, and make the Go placeholder match the others (an empty value).
• Python: move import sys out of the __main__ block (client.py:176). main() already uses it at lines 155-157.
• Python: mode="auto" is already the SDK default. Either remove it or add a comment saying it's set explicitly for teaching.
• Choose one approach to tool caching. Python lists the tools again on every query, while the others cache them when they connect. Pick one and explain it in a comment.

Tool-result handling is covered separately in Clients: fix what goes into a tool_result.

Acceptance criteria

• initialize from all five clients uses the same client-name pattern and version.
• ./tests/smoke-test.sh passes, and the launch command documented in each README works as written.