Imported from lewis-wow/snark (AGENTS.md). Install upstream with npx skills add lewis-wow/snark. Copyright stays with the author.

AGENTS.md

Ground rules (always)

• Be conservative, explicit, and boring.
• When unsure, ask; don’t guess.
• Make minimal, targeted changes; avoid refactors unless requested/necessary.
• Preserve existing structure, conventions, and tooling.
• Don’t add dependencies without strong justification.

TypeScript

• Write strict, idiomatic TS; follow the repo’s tsconfig and lint rules.
• No any (use unknown, generics, or proper types).
• Prefer interface for public shapes; type for unions/helpers.
• Prefer immutability (readonly, ReadonlyArray) where practical.
• Narrow with type guards; avoid assertions and ! except as a last resort.
• Prefer exhaustive handling (never checks) for unions.
• Treat caught errors as unknown and narrow before use.

Node.js

• Target the repo’s supported Node LTS (don’t assume versions; check config/docs).
• Prefer async/await; never swallow rejections.
• Avoid module top-level side effects (I/O, network, reading env, global mutations) unless explicitly intended.
• Env vars: validate centrally; read at runtime (not import-time); don’t mutate in app code (tests only with scoped setup/teardown).
• Error handling: rethrow with context; preserve cause when available; don’t throw strings.
• Library code should not log; CLIs may log intentionally with consistent exit codes.

Testing (Vitest)

• New logic requires tests unless truly trivial (types-only, re-exports, comments/formatting).
• Tests must be deterministic and isolated; avoid shared mutable state.
• Prefer behavioral tests; mock sparingly.
• No committed .only/.skip (unless explicitly justified).
• Bug fixes must include a regression test.
• Avoid snapshots unless they add clear value and are stable.

Style, docs, and security

• Follow existing formatting/lint; keep functions small and readable.
• Prefer named exports.
• Update docs/comments when behavior changes (comments explain “why”, not “what”).
• Never log secrets; validate/sanitize external inputs (paths/URLs/user data).
• Dependency adds must be justified (need, alternatives, maintenance/license/security impact).

MUST NOT

• Change public APIs or introduce breaking changes without explicit instruction.
• Perform stylistic rewrites or micro-optimizations.

Verify before committing

• Typecheck + lint + tests pass.
• New behavior has coverage (including failure paths); no unintended snapshot changes.
• No unnecessary diff churn; no accidental top-level side effects; env usage is validated and intentional.