Interface domain: Observer

Status: EXPERIMENTAL capability domain — NOT a normative specification (docs/interface-model.md §2). Adding required semantics here is a proposal, not an edit.

Purpose. Passive observation of governed systems without decision or enforcement authority: monitoring, anomaly detection, drift measurement.

Wire format. Emits schemas/wire/signal.schema.json objects; no distinct format in v0.1.

Open questions. Whether observer is a real boundary or a low-weight profile of environment+provenance — candidate for merging (docs/interface-model.md §2).

Formalization trigger. Evidence that observer-only projects need contract terms signal providers do not.