[week-05] 25620024 -- lab steps 2-4: week-01 tools as an MCP server, week-01 loop as an MCP host

[dragonash22]

Work in progress. This covers the week-05 lab only, steps 2 to 4 of 7. The graded assignment (negotiation market server) has not been started, so check_week05.py does not pass yet. Everything lives under submissions/25620024/week-05/lab/.

What I built

The week-01 tools now run behind an MCP server, and the week-01 agent loop is now an MCP host that uses them.

• lab/tools_server.py (step 2): calculator and read_file copied unchanged from week-01, each marked with @mcp.tool(). The hand-written TOOLS schema list is gone. The MCP SDK v2 (MCPServer) builds each tool's description from its docstring and its inputSchema from its type hints. The server runs over stdio by default, or over Streamable HTTP at http://127.0.0.1:8000/mcp with --http.
• lab/logs/step3-curl.txt (step 3): requests sent by hand with curl.
  • (A) a correct tools/list returns 200 with both tools.
  • (B) the same request without the Mcp-Method header returns 400 (-32020, header does not match the body).
  • (C) the same request without clientCapabilities in _meta returns 400 (-32602).
  • (D) tools/call calculator 48000+9500 returns 57500.
• lab/host.py (step 4): the week-01 loop with two changes. TOOLS now comes from list_tools(), converted to the Anthropic tool format. TOOLS_IMPL[name](**args) is now call_tool(name, args). The tool's is_error flag is also passed through to the model. The rest of the loop is untouched.
• lab/logs/step4-run-http-*.txt: the first host run over HTTP. It called read_file(notes.txt), then calculator("4 + 48000 + 9500 + 12000"), and answered 69504. The model left the date 2026-09-01 out of "every number" on its own.

What I tried and discarded

• My first check of the generated tool list read tool.inputSchema. That fails in SDK v2, where the Python attribute is input_schema (the JSON field is still inputSchema). The bug was in my check script, not in the server.
• Installing mcp>=2 replaced an existing mcp 1.25.0. Any old v1 code that imports mcp.server.fastmcp.FastMCP would now fail to import.
• git checkout -b stalled for several minutes on the Google Drive-synced working copy and left a stale .git/index.lock. I stopped the process, removed the lock, and created the branch with git branch + git symbolic-ref, which leaves the working tree untouched.

How to run

pip install "mcp>=2" anthropic          # mcp 2.2.0, anthropic 0.79.0 used here
cd submissions/25620024/week-05/lab
python tools_server.py --http           # terminal 1
python host.py                          # terminal 2; needs ANTHROPIC_API_KEY, model claude-sonnet-4-5

Remaining

• Lab step 5: choose the transport with MCP_SERVER, without touching the loop
• Lab step 6: attach the same server to a second client (Claude Code)
• Lab step 7: move write_note over without touching the host
• The assignment itself: market server with bearer tokens, scenarios.json, results.csv, logs/, auth_checks.txt, REPORT.md

Checklist

• python scripts/check_week05.py submissions/25620024/week-05 passes locally. It does not yet: only the .py parse check passes, and the other 5 fail because the assignment files do not exist.
• Run logs are committed under logs/ (lab logs)
• No API keys anywhere in the diff
• History is not squashed

🤖 Generated with Claude Code

[dragonash22]

Closed without merging: the real submission is Q00#263. Merging this would put lab commits on the fork's main and break 'git merge --ff-only upstream/main'.