Wards

Protective circles drawn around the ritual: nothing crosses them unexamined.

Technically: a Ward is middleware with four optional async hooks, registered with compile(wards=[...]) and applied as a pipeline in registration order — each Ward's output delta is the next one's input:

class Ward:
    def on_compile(self, manifest): ...                 # graph structure
    async def before_sigil(self, name, aether): ...
    async def after_sigil(self, name, aether, delta):   # transform or veto
        return delta
    async def on_omen(self, omen): ...                  # every engine event

The delta returned by after_sigil is what reducers, Seals, and SigilCompleted Omens see. Raising WardRejection vetoes the delta: a DeltaRejected Omen is emitted, the superstep aborts, and the Sigil's on_error policy applies when present. on_omen sees every Omen even without astream — build metrics and tracing without touching the engine.

Built-ins

Ward	Purpose
AuditWard(path)	One JSON Lines entry per applied delta (timestamp, sigil, delta) — a complete local audit trail
UsageWard()	Accumulates the Oracle usage counters that summon attaches to assistant messages; .summary() per Sigil and per Invocation
RedactWard(patterns)	Masks regex matches (API keys, emails) in every delta string before Seals and logs see them

Order matters: place RedactWard before AuditWard so the audit trail only ever contains masked content. TraceRecorder (tracing guide) is also a Ward.