spawn-unbriefed
A deny rule: it refuses a subagent spawned before the multi-agent skill loaded, and names what to run instead.
What it catches
A subagent spawned before the multi-agent skill loaded.
Why
Four decisions a spawn cannot be corrected for later are made before the child starts: which worktree it is cut from, which lease grades its writes, which model it runs, and that git stays with the orchestrator. The magus-multi-agent skill carries all four. Measured across 2,147 session transcripts: zero loads, under every name and every variant, while the two skills a hook DEMANDS loaded 415 times. A skill nobody is required to read is a skill nobody reads, and this workspace had already written that down before measuring it again here. It grades the session, never the prompt: it asks whether a marker file exists, so a handed-over prompt that merely mentions a denied command is untouched. Load Skill(magus-multi-agent) once and every later spawn in the session passes.
Seeing it
A verdict names its rule in brackets, which is how you got here:
deny [spawn-unbriefed]: ...
magus describe rule spawn-unbriefed prints the same entry at a terminal, and
magus describe rules lists every rule this workspace enforces.