monorepo: Skill for Codex

TypeScript best practices

Follow AGENTS.md and the repository lint configuration first.

Model the data

• Use discriminated unions when code has real variants. Avoid bags of optional fields that permit invalid combinations.
• Keep the simplest total type. Introduce branded primitives or non-empty tuples only when they prevent a demonstrated class of mistakes.
• Derive types from authoritative schemas and existing values with typeof, Pick, Omit, Parameters, ReturnType, or generated contracts.
• Parse external data at HTTP, queue, storage, configuration, and browser boundaries. Keep it unknown until validation succeeds.
• Prefer exhaustive switches. Make unhandled variants fail type checking.

Write honest TypeScript

• Avoid any, non-null assertions, and unchecked casts. When a library boundary requires a cast, keep it local and prove the invariant in code structure or a test.
• Prefer satisfies when validating an object without widening its literals.
• Use ===, ??, and optional chaining as specified by the project.
• Use one import per module and inline type specifiers for type-only names.
• Avoid nested ternaries. Use early returns or explicit branches.
• Use descriptive names and prefix genuinely unused variables with _.

React

• Let React Compiler handle memoization. Do not add memo, useMemo, or useCallback.
• Keep one component per file.
• Route all static user-facing text through i18n.

Verify

Test behavior through public seams. Prefer real framework primitives over mocks, and run the narrowest relevant typecheck, lint, and test tasks.