Reading the Sky Through Loops Topological Loop-Holonomy as a Portable Instrument: Galactic Spiral Streaming and the Secular Aberration Drift, with a Mapped Competence Surface

A portable instrument for reading coherent structure in vector fields on the sphere: a loop-holonomy estimator that walks closed loops through a fixed pentagon mesh and reads the enclosed circulation as topological closure-failure. Applied to Gaia DR3 stellar kinematics (~22.3 million stars after selection), it recovers the Milky Way's in-plane spiral streaming as coherent, parity-clean vorticity structure — 85 of 509 mesh rings exceeding 3σ against a pre-registered azimuth-shuffle null (chance ≈ 1), peaking at 7.0σ and surviving full Bonferroni correction; the holonomy reader agrees with a standard Jeans analysis on identical stars at the 0.1% level. Applied to a quasar reference-frame sample (Gaia DR3 × ICRF3, ~303k sources), it recovers the known secular aberration drift dipole in the per-source channel at 9.4σ (amplitude 0.4σ from the published value, apex within 6° of the published direction); the loop-holonomy channel recovers the direction but suppresses the amplitude by ~60%, a deficit localized to spatially-correlated proper-motion systematics and reported as a mapped instrument limitation rather than an error. The central result is framed as a competence surface: loop-holonomy is a low-frequency, global-phase reader that recovers where structure is and whether it is real more reliably than how much of it there is. Pre-registered bars, null batteries, failure diagnostics, and the substrate-independence lineage (one unmodified circulation routine spanning GPS stations, seismic creepmeters, and now galactic scales) are given in full. All topological machinery is implemented in-house under a stdlib/numpy discipline; established TDA libraries are cited as prior art rather than used as dependencies, so the provenance chain covers every line. Companion code, figures, and machine-readable results are included for reproducibility. Companion to the geodetic "Topological Tripwire" preprint (DOI 10.5281/zenodo.21287951); part of an ongoing independent research program.