Cold streams like GD-1 and Pal 5 are precision detectors for the thousands of dark subhalos ΛCDM requires, yet decades of monitoring have produced no unambiguous subhalo scar: the observed gaps disentangle into baryonic perturbers and intrinsic structure, with constraints sometimes undercutting the predicted abundance (Odenkirchen 2003; Yoon 2011; Bovy 2017).
The CDM mass spectrum does not stop at galaxy scales: thousands of starless subhalos must orbit the Milky Way, and fragile streams must record their passages. The prediction is the particle picture's most direct small-scale consequence, which makes the persistent ambiguity of the record a standing embarrassment rather than a neutral null.
SCT's expectation for the stream record is clean: no dark subhalos exist, because there is no dark matter particle to clump into them (P54). The dark-matter phenomenology at galactic scale is the coherent mesh contribution to Φ_eff (P50, P52), a smooth, slowly varying field with no orbiting lumps, so streams in SCT age gracefully, perturbed only by what can be seen: the bar, the spiral arms, molecular clouds, and the satellites already cataloged. The ambiguous record is the expected record; the gaps that resolve into baryonic causes and intrinsic structure are the data agreeing that nothing dark ever flew by.
The intrinsic structure has a registered source of its own: stream progenitors are cascade-debris fragments deposited with internal density variation (P25, P31), so streams need not be born uniform, and inherited substructure mimics nothing because it carries no flyby kinematics. The discriminant is sharp in both directions: a genuine subhalo passage leaves a characteristic velocity signature at the gap, a kinematic fingerprint inherited substructure and baryonic encounters do not duplicate. Gaia and LSST stream kinematics therefore make this sector one of SCT's cleanest near-term tests, the same no-particle keystone carrying the core-cusp sector (recid 127) and the missing-satellites count (recid 128). The mesh formalism is in Paper 13, From Chaos to Coherent Gravity.
Keystone economy: P54 alone makes the prediction, and the prediction is silence.
The kill is symmetric and registered: a confirmed stream gap carrying the full kinematic fingerprint of a dark perturber flyby, velocity offsets at the gap edges inexplicable by any cataloged baryonic body, would demonstrate orbiting dark substructure and refute the no-particle keystone directly. Conversely, ΛCDM is exposed in the same data: Gaia plus LSST stream censuses statistically excluding the predicted subhalo population would leave the particle picture without its small-scale mass spectrum. The streams will convict one framework or the other.