[changwangss]

Description

AWQ and SVDQuant maintain separate smoothing workflows. Extract an algorithm-independent SmoothEngine, SmoothGroup, and structural SmoothStrategy interface, and route both algorithms through the shared engine. New algorithms supply preparation, candidates, scoring, application, and cleanup without adding algorithm branches to the engine.

Preserve AWQ's activation/weight means, ratio/duo grid, QDQ loss, folding, and clipping synchronization; preserve SVDQuant's absmax statistics, Alpha/Beta grid, deployed-scale precision, and low-rank-aware scoring. Keep smoothing optional for SVDQuant and retain its search-all-groups-before-installation order. Existing configuration and SVDQuant smooth imports remain available.

Both algorithms now keep the first exact tie and share numerical-invalid candidate handling, logging, trial-state restoration, and cleanup. Execution errors, including OOM, propagate. AWQ retains its no-valid-candidate skip fallback; SVDQuant retains its error behavior. Joint AWQ + SVDQuant execution and broader model support remain follow-up work.

Type of Change

Refactor

Related Issues

Closes #2451

Validation

• 78 focused tests passed: 55 smoothing/strategy/SVDQuant pipeline tests and 23 existing AWQ replay/mapping and MXFP4/W4A16/Nunchaku compatibility tests.
• Runs used PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 and --noconftest to isolate self-contained tests; this is not a full repository test run.
• All pre-commit checks passed for changed files.
• Static comparison confirms extracted AWQ candidate/scoring closures and SVDQuant scoring preserve the original code apart from owner naming.

Checklist Before Submitting

• My code has been tested locally.
• Documentation has been updated as needed.
• New or updated tests are included where applicable.
• The CUDA CI has passed.