QEC Invariant Compendium: Baseline Equivalence, Trace-Indexed Reuse, Decoder Pipelines, and Dark-State Observables

This compendium presents four revised studies of deterministic computation, reusable intermediate results, and transformation invariants in belief-propagation diagnostics and quantum error-correction software. It connects earlier QSOL-IMC preprints with commit-pinned QEC source snapshots, reproducible experiments, and machine-checked mathematical models. The four studies examine baseline equivalence between min-sum decoding and unit-weight uniformly reweighted belief propagation; trace-indexed reuse of sign vectors and CRC32 values; the interaction of clipping, damping, freezing, and ternary projection in decoder transformation pipelines; and the interpretation of local “dark-state” observables in belief-propagation traces. The deposit contains four revised papers, editable manuscript sources, a dependency-free Lean 4 project, source snapshots, validation scripts, measured results, proof logs, provenance records, and integrity manifests. The formalization comprises 43 compiled theorem declarations. Empirical validation includes 576 paired decoder cases, 80 cached-versus-inline diagnostic comparisons, a reproduced reduction from 81 to 20 sign computations, 204 selected historical tests, and 18 synthetic dark-state scenario runs. The analysis also documents counterexamples and boundary conditions involving CRC32 collisions, cache provenance, source mutation, damping, NaN handling, transformation order, and the distinction between observed local stability and safe computational reuse. The Lean proofs establish properties of the stated exact mathematical models. They do not constitute a complete refinement proof for the Python/NumPy implementations or IEEE-754 arithmetic, nor do they establish physical quantum-hardware correctness or justify skipping live-decoder updates. Historical runtime improvements are identified as previously reported results, separate from the measurements reproduced in this deposit.