GPU/MPS-First Guards (Decision Memo)

Overview

Aspect	Details
Purpose	Record the guard design decisions enabling large-model execution.
Audience	Contributors and reviewers of guard measurement contracts.
Scope	Spectral + RMT guard contracts, accelerator-first design.
Source of truth	Guard implementations in `src/invarlock/guards/*.py`.

Quick Start

This is a decision memo; for implementation usage see Guards.

Concepts

Accelerator-first: guard math must run on CUDA/MPS without full SVD.
Approximation-only: iterative estimators and deterministic sampling.
Measurement contracts: estimator + sampling policy must be recorded in reports.

Reference

Goals

Device-resident guard computation for large models.
Reproducible approximations with fixed budgets.
Contract binding enforced at verification time.

Decisions

Single evidence mode: one canonical contract for each guard.
Spectral contract: track σ̂_max and degeneracy proxies (stable-rank drift, row/col norm collapse).
RMT contract: activation edge-risk score normalized by MP edge.
Verification gate: reports must record the measurement contract and hash.

Non-goals

Full-spectrum or exact SVD computations.
reports missing measurement contracts.

Troubleshooting

See Guards for operational guidance and guard configuration.

Observability

Contract hashes appear under spectral.measurement_contract_hash and rmt.measurement_contract_hash in reports.