typescript-narrowslisted

# The TypeScript Narrows One opinion per decision point. When TypeScript gives you five valid ways, this skill picks one and tells you why. ## How to use this skill Apply these opinions when writing new TypeScript code, refactoring existing code, or reviewing pull requests. Each opinion has a stance (what to do), a rationale (why), and do/don't examples in the reference files. **Severity tiers** indicate impact level: | Tag | Tier | Meaning | | --- | -------------- | ------------------------------------------------------------------- | | [B] | Bug prevention | Can cause runtime errors, data corruption, or silent wrong behavior | | [M] | Maintenance | Makes code harder to understand, refactor, or extend over time | | [S] | Style | Consistency and readability with no functional impact | **Exception clause:** All opinions allow exceptions when there is no other viable alternative. If you must deviate, document why in a code comment. Convenience alone is not a valid exception. ## Type Safety - Never use explicit `any`; use `unknown` and narrow before use. [B] - Use `unknown` for values of uncertain type to force callers to narrow. [B] - Restrict type assertions to proven-safe patterns only. [B] - Do not use the `!` non-null assertion operator; use proper null checks. [B] - Require explicit boolean comparisons; no truthy/falsy shortcuts. [B] - Type catch clause variables as