ADR 0001: Determinism and current formats

Status: accepted; updated for the current-format cleanup.

Context

Sounds are committed documents, rendered through Rust, the CLI, native playback, or Python. A refactor must preserve their samples and the agreement between an offline bounce and streaming playback. Historical DSP implementations added separate behavior paths without serving the current product.

Decision

Support SoundDoc/Song schema 2 and DSP engine 5 only. Omitted document pins select those current defaults; explicit unsupported revisions fail validation.

The current renderer uses deterministic f64 transcendental kernels in crates/tono-core/src/det.rs. RNG streams remain seeded by node position and named tracks. One block evaluator serves both the bounce and streaming; whole-buffer constructs use a rendered Player fallback.

Golden PCM hashes and block-size sweeps prove the current output. Investigate a changed hash before accepting it: organisation alone must not change sound. An intentional sound or format change requires an explicit revision decision and updated fixtures. Retaining every historical implementation is not policy.

Removing a node type is not a revision: a document that never used it renders the same bytes under the same engine pin, and one that did fails to parse with the unknown type named. 1.11.0 removed wavetable, bitcrush, downsample, ringmod, flanger, phaser, duck, convolve and granular on that basis; schema 2 and engine 5 stay.

Consequences

CI checks Linux with pinned and latest Rust. The algorithms avoid platform libm differences, but Windows/macOS builds are no longer funded or verified. Historical release claims belong to their changelog entries, not current support.

Useful proofs: tests/golden.rs, streaming byte-identity tests, tests/equivalence.rs, and tests/soak.rs in crates/tono-core.