Module guard 

Guard hook evaluation.

Library logic behind the binary’s hidden guard subcommand: the CLI handler reads the hook payload from stdin and the marker path from argv, calls guard_decision, and writes any deny verdict to stdout. Both layers fail open — a malformed payload or unreadable marker yields “allow”, so the guard can never brick a session.

Functions

codex_guard_decision

Codex’s hook contract blocks by returning { "decision": "block", "reason": "..." } on stdout. Keep this separate from Claude Code’s hookSpecificOutput shape so both harnesses use their native conventions.

guard_decision

Evaluate a PreToolUse hook payload (the JSON the harness sends on stdin) against marker. Returns the serialized deny verdict to print on stdout when the call is blocked, or None to allow (print nothing). An empty or malformed payload is treated as allow.

read_marker

Read and parse the guard marker. Missing or unparseable → None (the guard then allows everything — fail open).