Use whenever adding an e2e compiler-output test (our JS vs the reference compiler) — a new cluster case under `tasks/compiler_tests/`.
🧩 PARITY · Turn one divergence from the Original into a test per affected case (does not fix).
Use when starting any compiler task or session before touching parser/analyze/transform/ast/codegen/css/diagnostics code, before proposing a design or writing code, and when the task grows into a new layer and you need its PRD invariants.
🔪 SDT · verdict-directed review of backend codegen/transform. Use when auditing codegen/transform for smart-analyzer / dumb-codegen violations, or when porting a transform/codegen visitor from the Original.
The required unit-test format for `crates/**/src/**` — use when writing or reviewing a Rust `#[test]`, a test helper, or an `assert_*`. Not for `tasks/compiler_tests/` (use add-test) or `tasks/diagnostic_tests/` (use add-diagnostic-test).
PRD editorial standard for docs/. Use when writing a new PRD, extending one, or reviewing changes under docs/ — and when another skill needs the PRD rules.
Create a new diagnostic parity test case. Use when the user asks to add a diagnostic test, create a new `tasks/diagnostic_tests/cases/<name>` case, or capture a false positive/false negative against npm `svelte/compiler` before implementation.
Parse JS code through OXC and display ESTree JSON AST. Use proactively when implementing codegen, transforms, or debugging to understand how OXC represents a specific JS/TS construct in its AST. MUST use this skill before writing any new AST node construction in builder.rs, before implementing a new codegen visitor, or when unsure how OXC represents a JS pattern (destructuring, spread, optional chaining, etc.). Also use when debugging AST mismatch issues or when porting a new Svelte feature that involves JS expression handling.