Pitfalls

Claiming Enforcement from Event Coverage

A product may fire a hook without granting a blocking decision. Verify the output contract and failure behavior.

Ignoring Timeouts

A handler that fails open on timeout is an availability guardrail, not a hard security boundary. Keep it fast and move final authorization elsewhere.

Missing Alternate Paths

Blocking one shell command does not block the equivalent file tool, MCPMCPUSB-C for AI — one standard plug so any agent can connect to any data source or tool.The Model Context Protocol: an open standard (Anthropic, 2024) for connecting AI systems to external tools and data without building a custom integration for each one.Full definitionClose action, nested agentAgentA worker you delegate to: brief it, and it takes steps on its own. A chatbot answers; an agent acts.An LLM that runs tools in a loop toward a goal — it acts, checks the result, decides the next step, and repeats until done.Full definitionClose, IDE operation, or cloud executor.

Recursive Hooks

A completion hook that triggers more agent work can trigger itself again. Use explicit re-entry markers and bounded retries.

Untrusted Repository Scripts

Hook configuration and scripts checked into an untrusted repository can execute with developer credentials. Require review and managed allowlists before activation.

Non-Deterministic Decisions in a Deterministic Slot

PromptPromptThe brief. Closer to writing instructions for a new contractor than to programming.The text you give the model — question, instructions, context. Its quality shapes the quality of the output.Full definitionClose or agent handlers can add judgment, but they do not turn the hook into deterministic policy. Label model-derived decisions and retain the evidence.

Falsification Checklist

• Does the handler still control the action when it crashes or times out?
• Do nested agents and MCP tools traverse the same event?
• Can repository code disable or replace the hook?
• Is the release check repeated outside the local agent runtime?