substrateLocalAccessCert

Gravity Track 2.C closes the measurement-access step beyond Session 111. Session 111 showed that a nonzero matter-section readout of a linear joint operator forces the channel to be amplitude-linear; pure-tensor factorization was sufficient but not necessary. The remaining gap was that the physical channel is operationally obtained by such a readout.

Substrate locality / measurement-access supplies that gap: every operational channel on the joint substrate $\mathrm{Signal8}\otimes\mathrm{Signal8}$ is a recognition probe. Fix a matter reference $\psi_0$, apply the joint operator $R_J$ once, read channel coordinate $i_0$, and normalise by a calibration $\chi\neq 0$. The induced formula $R_C\varphi=\chi^{-1}\cdot\mathrm{extractSecond}_{i_0}(R_J(\mathrm{insertFirst},\psi_0,\varphi))$ is then, by definition, a joint section readout.

The structure SubstrateLocalAccessCert records the full implication chain access $\to$ section readout $\to$ amplitude-linearity, the density-only no-go, the factorization bridge, and a non-vacuous canonical witness.

Field-by-field structure constructor; no new mathematics.

• section_readout_from_access is the one-line application of sectionReadout_of_arisesFromSubstrateAccess.
• amplitude_linear_from_access applies isAmplitudeLinear_channel_of_arisesFromSubstrateAccess (itself via the section-readout link).
• density_only_collapse applies channel_eq_zero_of_density_only_of_arisesFromSubstrateAccess.
• no_nontrivial_density_only is exactly not_exists_nontrivial_density_only_channel_with_substrateAccess.
• factorization_implies_access introduces the factorization data and applies arisesFromSubstrateAccess_of_pureTensorFactorization.
• canonical_witness is canonicalCyclicJointOperator_arisesFromRecognitionProbe (recognition probe on the Session-87 cyclic joint operator).

This is the module's master packaging object for the substrate locality / measurement-access principle. Downstream, substrateLocalAccessCert_inhabited is the one-line non-emptiness theorem ⟨substrateLocalAccessCert⟩, which opens the module's "one-statement substrate locality theorem" section.

In the Recognition gravity track it retires the Session-111 assumption that the physical channel is a section readout: under substrate access that readout is definitional, so amplitude-linearity of the operational channel follows from joint linearity alone. The density-only collapse and existence no-go rule out classical density-only alternatives on the eight-tick joint substrate. The factorization bridge keeps continuity with earlier pure-tensor hypotheses, and the canonical cyclic witness shows the principle is inhabited rather than vacuous.

Framework landmarks: eight-tick Signal8 octave (T7), joint substrate as the measurement arena, and the forced amplitude-linear channel law that feeds later gravity/quantum-channel forcing.