Houdini Python - traps and house rules

Staged by the 2026-11-08 round-2 baseline eval (ClaudeCode/evals/houdini-round2/ANALYSIS.md): with only the Houdini MCP the model passed both cases 4/4 (ROP frame range, object_merge world position); the skill was never opened. The MCP tools already carry part of the guard (set_parameters reports expression_kept and takes override_expression; export_file reports wrote_files). The Python tutorial (batch node creation, parameter animation, scene I/O, callbacks) is cut. What stays are the measured traps.

Order of preference: MCP tool > build_network > execute_python (execute_python for what no tool does, e.g. running a ROP with an explicit range or writing a read-back file from inside Houdini).

Traps (details and code in reference/)