configuration for the typescript skill using opencode

sources/opencode/skills/typescript/SKILL.md

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+---
+name: typescript
+description: TypeScript development guidelines - strict config, functional programming, best practices
+metadata:
+  language: typescript
+  audience: developers
+---
+
+## Configuration
+
+When working in a TypeScript project:
+
+1. **Check for tsconfig.json** - Always verify the project has a `tsconfig.json`
+2. **If missing**: Install `typescript` as dev dependency, then run `npx tsc --init`
+3. **Use strictest options** - Configure the strictest possible compilerOptions:
+   - `strict: true`
+   - `noUncheckedIndexedAccess: true`
+   - `noImplicitReturns: true`
+   - `noFallthroughCasesInSwitch: true`
+   - `exactOptionalPropertyTypes: true`
+   - `noImplicitOverride: true`
+
+Reference: https://www.typescriptlang.org/tsconfig/
+
+## Functional Programming
+
+Favor functional programming when coding in TypeScript:
+
+- **Immutability** - Use `const`, spread operators, `Object.freeze()`, immutable data structures
+- **Pure functions** - Same input always produces same output, no side effects
+- **No side-effects** - Prefer pure functions, isolate side effects to specific layers
+- **No throw** - Use Result/Either types for error handling instead of exceptions
+
+## Type Safety
+
+- Prefer `type` over `interface` for unions and primitives
+- Use `unknown` over `any` - always narrow types before use
+- Enable `strictNullChecks` - handle null/undefined explicitly
+- Use utility types (`Partial`, `Required`, `Readonly`, `Record`, etc.)
+- Avoid `as` assertions; prefer type guards