init: common-skills v1

skills/typescript/SKILL.md

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+---
+name: typescript-skill
+description: TypeScript coding patterns and type safety guide. Use when writing, reviewing, or debugging TypeScript code.
+---
+
+# TypeScript Skill
+
+## Key Rules
+
+### Always Prefer Explicit Types
+```typescript
+// Bad
+const process = (data: any) => data.value;
+
+// Good
+interface GameState { value: number; }
+const process = (data: GameState): number => data.value;
+```
+
+### Use `unknown` Instead of `any`
+```typescript
+// Bad
+function parse(input: any) { return input.name; }
+
+// Good
+function parse(input: unknown): string {
+  if (typeof input === 'object' && input !== null && 'name' in input) {
+    return String((input as { name: unknown }).name);
+  }
+  throw new Error('Invalid input');
+}
+```
+
+### Prefer `const` Assertions for Literals
+```typescript
+const DIRECTIONS = ['up', 'down', 'left', 'right'] as const;
+type Direction = typeof DIRECTIONS[number]; // 'up' | 'down' | 'left' | 'right'
+```
+
+## Common Patterns
+
+| Pattern | Use Case |
+|---------|----------|
+| `type` | Unions, intersections, primitives |
+| `interface` | Object shapes (extendable) |
+| `enum` | Named constants (prefer `as const` for simple cases) |
+| `generic <T>` | Reusable, type-safe utilities |

skills/typescript/evals/evals.json

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+{
+  "skill_name": "typescript",
+  "evals": [
+    {
+      "id": 1,
+      "prompt": "How do I avoid using 'any' type in TypeScript?",
+      "expected_output": "Explains using 'unknown' instead of 'any', with type guards, and shows interface/type definitions as alternatives."
+    },
+    {
+      "id": 2,
+      "prompt": "Show me how to create a type-safe function in TypeScript that processes a list of items",
+      "expected_output": "Demonstrates a generic function with <T> type parameter, proper return type annotation, and no use of 'any'."
+    },
+    {
+      "id": 3,
+      "prompt": "What's the difference between type and interface in TypeScript?",
+      "expected_output": "Explains that interfaces are extendable and better for object shapes, types support unions/intersections, with concrete examples of each."
+    }
+  ]
+}