Fable is good at instruction following, so just adding the snippet I mentioned in the post is good enough for the most cases.

There is a way to control tool invocations at the harness level when writing skills or agents.

Example: ~/.claude/agents/critic.md

    ---
    name: critic
    description: >
      Plan Critic. Reviews an implementation plan. Use before the implementation.
    tools: Read, Agent
    ---

For Claude skills, the frontmatter is different, the keys are:

    allowed-tools: Read Grep
    disallowed-tools: WebSearch Glob

https://code.claude.com/docs/en/tools-reference