External language authoring hardening — 2026-07-21

Architectural delta

This iteration removes the remaining Wist- and text-shaped assumptions from the public external-language path:

• added LanguageArtifactKind<T> and typed artifact contracts;
• moved route compatibility failures from runtime casts to language planning;
• made the pipeline entry artifact configurable;
• allowed planning-only languages without fake backend/runtime selections;
• added UniversalToolchain.LanguageAuthoring, which creates descriptors and implementations from one registration source;
• added typed transformer and executor interfaces;
• bound every runtime executor to the exact backend contribution selected by the plan;
• require explicit determinism and host-interop traits instead of inferring safety from arbitrary delegates;
• made runtime determinism and host-interop policies enforceable provider contracts;
• changed manifests and lock snapshots to schema v3 while retaining v1/v2 readers;
• replaced the Wist-based beginner template with a standalone non-Wist template;
• replaced the Acme sample with an independent parser and two independent backends;
• synchronized the canonical Wist.sln project graph; the redundant .slnx mirror was later retired to avoid drift.

Compatibility

The old string constructor for LanguageExecutionRequest, untyped artifact IDs, schema-v1/v2 manifests and the legacy Wist runtime adapter remain supported. New code should use typed artifact kinds and the authoring builder.

Honest boundary

This is a typed contribution/route language SDK, not yet a declarative grammar or type-system workbench. Grammar, binding, type rules and operation-definition conveniences remain future layers.