Native QEC Program IR

QecProgram in src/qec/mod.rs is a measurement-record IR for QEC workloads that need detectors, logical observables, postselection, expectation metadata, and Pauli-noise annotations before sampler lowering. It is separate from Circuit so measurement-record programs do not need to fit final-measurement OpenQASM semantics.

QecOp stores gates, basis measurements, MPP-style Pauli-product measurements, resets, detector rows, observable includes, expectation-value metadata, postselection predicates, noise annotations, and tick separators. Record references can be absolute indices or rec[-k] style lookbacks. Construction validates qubit bounds, gate arity, finite coordinates and coefficients, finite probabilities, and measurement-record scope. Detector, observable, and postselection rows can be resolved to absolute measurement indices for later compilation into packed samplers.

Parsing

parse_qec_program and QecProgram::from_text parse the native QEC text subset used by current benchmark planning: H, S, S_DAG, T, T_DAG, CX, CZ, R/RX/RY, M/MX/MY, MR variants, MPP, DETECTOR, OBSERVABLE_INCLUDE, POSTSELECT, EXP_VAL, Pauli-noise instructions, TICK, QUBIT_COORDS, SHIFT_COORDS, and flattened REPEAT blocks. The parser resolves rec[-k] references while building the program. Numeric arguments on basis measurements, such as M(0.001), lower to pre-measurement Pauli flips that affect the measurement record.

Lowering

compile_qec_program_rows lowers basis measurements and MPP records into the same packed X/Z Pauli row representation used by the compiled sampler internals. It also carries detector, observable, and postselection rows forward as absolute measurement-record indices. Detector, observable, and postselection projection uses PackedShots::parity_rows, so the QEC layer reuses the existing packed parity engine instead of maintaining a second one. This is a sampler-lowering artifact, not an execution engine. Gate, reset, and noise execution lives in run_qec_program; EXP_VAL remains unsupported in the packed runner until estimator semantics land.

Execution

run_qec_program is the scalable native QEC execution path. It lowers Clifford-compatible QEC programs into the existing packed compiled sampler, so sampling uses packed measurement records instead of dense amplitudes. It supports Clifford gates, basis resets and measurements, MPP, detectors, observables, postselection, Pauli-noise annotations, and optional raw-measurement retention. Noisy Clifford programs compile X_ERROR, Z_ERROR, DEPOLARIZE1, and correlated DEPOLARIZE2 events into packed sensitivity rows, then XOR those rows into the packed measurement records. Non-Clifford gates and EXP_VAL reject clearly until their production strategies land.

run_qec_program_reference is the small-program correctness oracle. It runs one state-vector simulation per shot and supports Pauli-noise annotations, but it is not the production performance path.