The Structural Control Architecture: Three Channels and a Governed Seam

The first paper of this series proved that telemetry does not determine structural state — exactly not in the blind set, and within the noise floor below resolution — and the second measured where telemetry-side governance actually ends: a fixed-gate estimator earning its envelope on public run-to-failure benchmarks, and an integrity governor whose adversarial ladder closes at a named boundary, the statistically faithful forgery that evades a telemetry-only observer in the majority of trials — with the caught minority owed to imperfect matching, not to any escape from the limit. This paper reports the construction those two results leave standing: the Structural Control Architecture (SCA), a monitoring stack built as three channels with distinct, non-interchangeable jobs — an identity-and-provenance channel that authenticates which component and which sensor is speaking; a structural-state channel that asserts state only inside the non-identifiability contract; and an authenticated-telemetry channel that vouches for stream admissibility and record integrity — composed under an integrity governor with guarded finalisation, an append-only audit record, and bounded portability. The composition law is the paper's centre: no channel's output is ground truth; agreement is composed evidence with each channel's maturity carried visibly; and the two residues the series' theorems prove irreducible — the sub-resolution blind set and live material-state truth — are stated as owned residues and frontier items, not papered over. The architecture claims geometry and composition, never validation: its evidential imports are the second paper's measured ladder and archives, its material-side elements stay at their declared proposed strata, and every unit holds advisory-only authority under the programme's interface contract. The distance from this geometry to a running stack is named, bounded, and on the frontier list.