Architecture Decision Records (ADR)

Short, durable notes for why the codebase looks the way it does. They complement narrative docs (architecture.md). Historical 0.2 planning notes live in the archive.

ADR	Title
0001-record-architecture-decisions.md	Why we keep ADRs
0002-gradient-operators-fd-vs-spectral.md	FD vs spectral operators (direction)
0003-time-integrator-interface.md	Time integrator interface contracts
0004-execution-layer.md	Execution layer for 0.2 — minimal homegrown, no Kokkos
0005-fft-interface.md	FFT interface — split host and device transforms
0006-precision-policy.md	Precision policy — template on RealType, instantiate double
0007-decomposition-splitter.md	Decomposition splitter — in-repo, HeFFTe as FFT-only dependency
0008-io-formats.md	I/O and checkpoint formats for 0.2

New ADRs: copy the template sections from 0001, use the next number, and add a row here.