fix(#1): Address code review findings

- Convert ApiResponse to discriminated union for type-safe error handling
- Add HealthStatus type with HealthState literal union
- Make BaseEntity fields readonly for immutability
- Add GlobalExceptionFilter with structured logging
- Add port validation with clear error messages in main.ts
- Improve parseDate to log warnings for invalid dates
- Add comprehensive Button tests (variants, onClick, disabled)
- Add slugify edge case tests (empty, special chars, numbers)
- Create ESLint configs for all packages
- Remove compiled JS files from src directories
- Convert .prettierrc.js to .prettierrc.json

Refs #1

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitignore

@@ -7,6 +7,16 @@ dist
 .next
 .turbo
 
+# Compiled source (prevent accidental commits)
+apps/*/src/**/*.js
+apps/*/src/**/*.d.ts
+apps/*/src/**/*.js.map
+apps/*/src/**/*.d.ts.map
+packages/*/src/**/*.js
+packages/*/src/**/*.d.ts
+packages/*/src/**/*.js.map
+packages/*/src/**/*.d.ts.map
+
 # IDE
 .idea
 .vscode

.prettierrc.js

@@ -1,3 +0,0 @@
-import config from "@mosaic/config/prettier";
-
-export default config;

.prettierrc.json

@@ -0,0 +1,10 @@
+{
+  "semi": true,
+  "singleQuote": false,
+  "tabWidth": 2,
+  "trailingComma": "es5",
+  "printWidth": 100,
+  "bracketSpacing": true,
+  "arrowParens": "always",
+  "endOfLine": "lf"
+}

apps/api/eslint.config.js

@@ -0,0 +1,16 @@
+import nestjsConfig from "@mosaic/config/eslint/nestjs";
+
+export default [
+  ...nestjsConfig,
+  {
+    languageOptions: {
+      parserOptions: {
+        project: ["./tsconfig.json"],
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+  },
+  {
+    ignores: ["dist/**", "node_modules/**", "**/*.test.ts", "**/*.spec.ts"],
+  },
+];

apps/api/src/app.controller.d.ts

@@ -1,14 +0,0 @@
-import { AppService } from "./app.service";
-import type { ApiResponse } from "@mosaic/shared/types";
-interface HealthStatus {
-    status: string;
-    timestamp: string;
-}
-export declare class AppController {
-    private readonly appService;
-    constructor(appService: AppService);
-    getHello(): string;
-    getHealth(): ApiResponse<HealthStatus>;
-}
-export {};
-//# sourceMappingURL=app.controller.d.ts.map

apps/api/src/app.controller.d.ts.map

@@ -1 +0,0 @@
-{"version":3,"file":"app.controller.d.ts","sourceRoot":"","sources":["app.controller.ts"],"names":[],"mappings":"AACA,OAAO,EAAE,UAAU,EAAE,MAAM,eAAe,CAAC;AAC3C,OAAO,KAAK,EAAE,WAAW,EAAE,MAAM,sBAAsB,CAAC;AAExD,UAAU,YAAY;IACpB,MAAM,EAAE,MAAM,CAAC;IACf,SAAS,EAAE,MAAM,CAAC;CACnB;AAED,qBACa,aAAa;IACZ,OAAO,CAAC,QAAQ,CAAC,UAAU;gBAAV,UAAU,EAAE,UAAU;IAGnD,QAAQ,IAAI,MAAM;IAKlB,SAAS,IAAI,WAAW,CAAC,YAAY,CAAC;CASvC"}

apps/api/src/app.controller.js

@@ -1,50 +0,0 @@
-"use strict";
-var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
-    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
-    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
-    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
-    return c > 3 && r && Object.defineProperty(target, key, r), r;
-};
-var __metadata = (this && this.__metadata) || function (k, v) {
-    if (typeof Reflect === "object" && typeof Reflect.metadata === "function") return Reflect.metadata(k, v);
-};
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.AppController = void 0;
-const common_1 = require("@nestjs/common");
-const app_service_1 = require("./app.service");
-let AppController = class AppController {
-    appService;
-    constructor(appService) {
-        this.appService = appService;
-    }
-    getHello() {
-        return this.appService.getHello();
-    }
-    getHealth() {
-        return {
-            success: true,
-            data: {
-                status: "healthy",
-                timestamp: new Date().toISOString(),
-            },
-        };
-    }
-};
-exports.AppController = AppController;
-__decorate([
-    (0, common_1.Get)(),
-    __metadata("design:type", Function),
-    __metadata("design:paramtypes", []),
-    __metadata("design:returntype", String)
-], AppController.prototype, "getHello", null);
-__decorate([
-    (0, common_1.Get)("health"),
-    __metadata("design:type", Function),
-    __metadata("design:paramtypes", []),
-    __metadata("design:returntype", Object)
-], AppController.prototype, "getHealth", null);
-exports.AppController = AppController = __decorate([
-    (0, common_1.Controller)(),
-    __metadata("design:paramtypes", [app_service_1.AppService])
-], AppController);
-//# sourceMappingURL=app.controller.js.map

apps/api/src/app.controller.js.map

@@ -1 +0,0 @@
-{"version":3,"file":"app.controller.js","sourceRoot":"","sources":["app.controller.ts"],"names":[],"mappings":";;;;;;;;;;;;AAAA,2CAAiD;AACjD,+CAA2C;AASpC,IAAM,aAAa,GAAnB,MAAM,aAAa;IACK;IAA7B,YAA6B,UAAsB;QAAtB,eAAU,GAAV,UAAU,CAAY;IAAG,CAAC;IAGvD,QAAQ;QACN,OAAO,IAAI,CAAC,UAAU,CAAC,QAAQ,EAAE,CAAC;IACpC,CAAC;IAGD,SAAS;QACP,OAAO;YACL,OAAO,EAAE,IAAI;YACb,IAAI,EAAE;gBACJ,MAAM,EAAE,SAAS;gBACjB,SAAS,EAAE,IAAI,IAAI,EAAE,CAAC,WAAW,EAAE;aACpC;SACF,CAAC;IACJ,CAAC;CACF,CAAA;AAlBY,sCAAa;AAIxB;IADC,IAAA,YAAG,GAAE;;;;6CAGL;AAGD;IADC,IAAA,YAAG,EAAC,QAAQ,CAAC;;;;8CASb;wBAjBU,aAAa;IADzB,IAAA,mBAAU,GAAE;qCAE8B,wBAAU;GADxC,aAAa,CAkBzB"}

apps/api/src/app.controller.ts

@@ -1,11 +1,7 @@
 import { Controller, Get } from "@nestjs/common";
 import { AppService } from "./app.service";
-import type { ApiResponse } from "@mosaic/shared";
-
-interface HealthStatus {
-  status: string;
-  timestamp: string;
-}
+import type { ApiResponse, HealthStatus } from "@mosaic/shared";
+import { successResponse } from "@mosaic/shared";
 
 @Controller()
 export class AppController {
@@ -18,12 +14,9 @@ export class AppController {
 
   @Get("health")
   getHealth(): ApiResponse<HealthStatus> {
-    return {
-      success: true,
-      data: {
-        status: "healthy",
-        timestamp: new Date().toISOString(),
-      },
-    };
+    return successResponse({
+      status: "healthy",
+      timestamp: new Date().toISOString(),
+    });
   }
 }

apps/api/src/app.module.d.ts

@@ -1,3 +0,0 @@
-export declare class AppModule {
-}
-//# sourceMappingURL=app.module.d.ts.map

apps/api/src/app.module.d.ts.map

@@ -1 +0,0 @@
-{"version":3,"file":"app.module.d.ts","sourceRoot":"","sources":["app.module.ts"],"names":[],"mappings":"AAIA,qBAKa,SAAS;CAAG"}

apps/api/src/app.module.js

@@ -1,23 +0,0 @@
-"use strict";
-var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
-    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
-    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
-    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
-    return c > 3 && r && Object.defineProperty(target, key, r), r;
-};
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.AppModule = void 0;
-const common_1 = require("@nestjs/common");
-const app_controller_1 = require("./app.controller");
-const app_service_1 = require("./app.service");
-let AppModule = class AppModule {
-};
-exports.AppModule = AppModule;
-exports.AppModule = AppModule = __decorate([
-    (0, common_1.Module)({
-        imports: [],
-        controllers: [app_controller_1.AppController],
-        providers: [app_service_1.AppService],
-    })
-], AppModule);
-//# sourceMappingURL=app.module.js.map

apps/api/src/app.module.js.map

@@ -1 +0,0 @@
-{"version":3,"file":"app.module.js","sourceRoot":"","sources":["app.module.ts"],"names":[],"mappings":";;;;;;;;;AAAA,2CAAwC;AACxC,qDAAiD;AACjD,+CAA2C;AAOpC,IAAM,SAAS,GAAf,MAAM,SAAS;CAAG,CAAA;AAAZ,8BAAS;oBAAT,SAAS;IALrB,IAAA,eAAM,EAAC;QACN,OAAO,EAAE,EAAE;QACX,WAAW,EAAE,CAAC,8BAAa,CAAC;QAC5B,SAAS,EAAE,CAAC,wBAAU,CAAC;KACxB,CAAC;GACW,SAAS,CAAG"}

apps/api/src/app.service.d.ts

@@ -1,4 +0,0 @@
-export declare class AppService {
-    getHello(): string;
-}
-//# sourceMappingURL=app.service.d.ts.map

apps/api/src/app.service.d.ts.map

@@ -1 +0,0 @@
-{"version":3,"file":"app.service.d.ts","sourceRoot":"","sources":["app.service.ts"],"names":[],"mappings":"AAEA,qBACa,UAAU;IACrB,QAAQ,IAAI,MAAM;CAGnB"}

apps/api/src/app.service.js

@@ -1,20 +0,0 @@
-"use strict";
-var __decorate = (this && this.__decorate) || function (decorators, target, key, desc) {
-    var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d;
-    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc);
-    else for (var i = decorators.length - 1; i >= 0; i--) if (d = decorators[i]) r = (c < 3 ? d(r) : c > 3 ? d(target, key, r) : d(target, key)) || r;
-    return c > 3 && r && Object.defineProperty(target, key, r), r;
-};
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.AppService = void 0;
-const common_1 = require("@nestjs/common");
-let AppService = class AppService {
-    getHello() {
-        return "Mosaic Stack API";
-    }
-};
-exports.AppService = AppService;
-exports.AppService = AppService = __decorate([
-    (0, common_1.Injectable)()
-], AppService);
-//# sourceMappingURL=app.service.js.map

apps/api/src/app.service.js.map

@@ -1 +0,0 @@
-{"version":3,"file":"app.service.js","sourceRoot":"","sources":["app.service.ts"],"names":[],"mappings":";;;;;;;;;AAAA,2CAA4C;AAGrC,IAAM,UAAU,GAAhB,MAAM,UAAU;IACrB,QAAQ;QACN,OAAO,kBAAkB,CAAC;IAC5B,CAAC;CACF,CAAA;AAJY,gCAAU;qBAAV,UAAU;IADtB,IAAA,mBAAU,GAAE;GACA,UAAU,CAItB"}

apps/api/src/filters/global-exception.filter.ts

@@ -0,0 +1,69 @@
+import { ExceptionFilter, Catch, ArgumentsHost, HttpException, HttpStatus } from "@nestjs/common";
+import type { Request, Response } from "express";
+import { randomUUID } from "crypto";
+
+interface ErrorResponse {
+  success: false;
+  message: string;
+  errorId: string;
+  timestamp: string;
+  path: string;
+  statusCode: number;
+}
+
+@Catch()
+export class GlobalExceptionFilter implements ExceptionFilter {
+  catch(exception: unknown, host: ArgumentsHost) {
+    const ctx = host.switchToHttp();
+    const response = ctx.getResponse<Response>();
+    const request = ctx.getRequest<Request>();
+
+    const errorId = randomUUID();
+    const timestamp = new Date().toISOString();
+
+    let status = HttpStatus.INTERNAL_SERVER_ERROR;
+    let message = "An unexpected error occurred";
+
+    if (exception instanceof HttpException) {
+      status = exception.getStatus();
+      const exceptionResponse = exception.getResponse();
+      message =
+        typeof exceptionResponse === "string"
+          ? exceptionResponse
+          : ((exceptionResponse as { message?: string }).message ?? message);
+    } else if (exception instanceof Error) {
+      message = exception.message;
+    }
+
+    const isProduction = process.env.NODE_ENV === "production";
+
+    // Structured error logging
+    const logPayload = {
+      level: "error",
+      errorId,
+      timestamp,
+      method: request.method,
+      url: request.url,
+      statusCode: status,
+      message: exception instanceof Error ? exception.message : String(exception),
+      stack: !isProduction && exception instanceof Error ? exception.stack : undefined,
+    };
+
+    console.error(isProduction ? JSON.stringify(logPayload) : logPayload);
+
+    // Sanitized client response
+    const errorResponse: ErrorResponse = {
+      success: false,
+      message:
+        isProduction && status === HttpStatus.INTERNAL_SERVER_ERROR
+          ? "An unexpected error occurred"
+          : message,
+      errorId,
+      timestamp,
+      path: request.url,
+      statusCode: status,
+    };
+
+    response.status(status).json(errorResponse);
+  }
+}

apps/api/src/main.d.ts

@@ -1,2 +0,0 @@
-export {};
-//# sourceMappingURL=main.d.ts.map

apps/api/src/main.d.ts.map

@@ -1 +0,0 @@
-{"version":3,"file":"main.d.ts","sourceRoot":"","sources":["main.ts"],"names":[],"mappings":""}

apps/api/src/main.js

@@ -1,16 +0,0 @@
-"use strict";
-Object.defineProperty(exports, "__esModule", { value: true });
-const core_1 = require("@nestjs/core");
-const app_module_1 = require("./app.module");
-async function bootstrap() {
-    const app = await core_1.NestFactory.create(app_module_1.AppModule);
-    app.enableCors();
-    const port = process.env["PORT"] ?? 3001;
-    await app.listen(port);
-    console.log(`API running on http://localhost:${port}`);
-}
-bootstrap().catch((err) => {
-    console.error("Failed to start application:", err);
-    process.exit(1);
-});
-//# sourceMappingURL=main.js.map

apps/api/src/main.js.map

@@ -1 +0,0 @@
-{"version":3,"file":"main.js","sourceRoot":"","sources":["main.ts"],"names":[],"mappings":";;AAAA,uCAA2C;AAC3C,6CAAyC;AAEzC,KAAK,UAAU,SAAS;IACtB,MAAM,GAAG,GAAG,MAAM,kBAAW,CAAC,MAAM,CAAC,sBAAS,CAAC,CAAC;IAChD,GAAG,CAAC,UAAU,EAAE,CAAC;IAEjB,MAAM,IAAI,GAAG,OAAO,CAAC,GAAG,CAAC,MAAM,CAAC,IAAI,IAAI,CAAC;IACzC,MAAM,GAAG,CAAC,MAAM,CAAC,IAAI,CAAC,CAAC;IAEvB,OAAO,CAAC,GAAG,CAAC,mCAAmC,IAAI,EAAE,CAAC,CAAC;AACzD,CAAC;AAED,SAAS,EAAE,CAAC,KAAK,CAAC,CAAC,GAAY,EAAE,EAAE;IACjC,OAAO,CAAC,KAAK,CAAC,8BAA8B,EAAE,GAAG,CAAC,CAAC;IACnD,OAAO,CAAC,IAAI,CAAC,CAAC,CAAC,CAAC;AAClB,CAAC,CAAC,CAAC"}

apps/api/src/main.ts

@@ -1,17 +1,61 @@
 import { NestFactory } from "@nestjs/core";
 import { AppModule } from "./app.module";
+import { GlobalExceptionFilter } from "./filters/global-exception.filter";
+
+function getPort(): number {
+  const portEnv = process.env.PORT;
+
+  if (portEnv === undefined || portEnv === "") {
+    return 3001;
+  }
+
+  const port = parseInt(portEnv, 10);
+
+  if (isNaN(port)) {
+    throw new Error(`Invalid PORT environment variable: "${portEnv}". PORT must be a number.`);
+  }
+
+  if (port < 1 || port > 65535) {
+    throw new Error(
+      `Invalid PORT environment variable: ${String(port)}. PORT must be between 1 and 65535.`
+    );
+  }
+
+  return port;
+}
 
 async function bootstrap() {
   const app = await NestFactory.create(AppModule);
+
+  app.useGlobalFilters(new GlobalExceptionFilter());
   app.enableCors();
 
-  const port = process.env["PORT"] ?? 3001;
+  const port = getPort();
   await app.listen(port);
 
-  console.log(`API running on http://localhost:${port}`);
+  console.log(`API running on http://localhost:${String(port)}`);
 }
 
 bootstrap().catch((err: unknown) => {
-  console.error("Failed to start application:", err);
+  const isProduction = process.env.NODE_ENV === "production";
+  const errorMessage = err instanceof Error ? err.message : String(err);
+  const errorStack = err instanceof Error ? err.stack : undefined;
+
+  if (isProduction) {
+    console.error(
+      JSON.stringify({
+        level: "error",
+        message: "Failed to start application",
+        error: errorMessage,
+        timestamp: new Date().toISOString(),
+      })
+    );
+  } else {
+    console.error("Failed to start application:", errorMessage);
+    if (errorStack) {
+      console.error(errorStack);
+    }
+  }
+
   process.exit(1);
 });

apps/web/eslint.config.js

@@ -0,0 +1,16 @@
+import nextjsConfig from "@mosaic/config/eslint/nextjs";
+
+export default [
+  ...nextjsConfig,
+  {
+    languageOptions: {
+      parserOptions: {
+        project: ["./tsconfig.json"],
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+  },
+  {
+    ignores: [".next/**", "node_modules/**"],
+  },
+];

apps/web/package.json

@@ -6,8 +6,8 @@
     "build": "next build",
     "dev": "next dev --turbopack --port 3000",
     "start": "next start",
-    "lint": "next lint",
-    "lint:fix": "next lint --fix",
+    "lint": "eslint \"src/**/*.{ts,tsx}\"",
+    "lint:fix": "eslint \"src/**/*.{ts,tsx}\" --fix",
     "typecheck": "tsc --noEmit",
     "clean": "rm -rf .next",
     "test": "vitest run",

apps/web/src/app/page.tsx

@@ -4,9 +4,7 @@ export default function Home() {
   return (
     <main className="flex min-h-screen flex-col items-center justify-center p-24">
       <h1 className="text-4xl font-bold mb-8">Mosaic Stack</h1>
-      <p className="text-lg text-gray-600 mb-8">
-        Welcome to the Mosaic Stack monorepo
-      </p>
+      <p className="text-lg text-gray-600 mb-8">Welcome to the Mosaic Stack monorepo</p>
       <div className="flex gap-4">
         <Button variant="primary">Get Started</Button>
         <Button variant="secondary">Learn More</Button>

packages/config/eslint/nestjs.js

@@ -4,9 +4,9 @@ export default [
   ...baseConfig,
   {
     rules: {
-      "@typescript-eslint/interface-name-prefix": "off",
       "@typescript-eslint/explicit-function-return-type": "off",
       "@typescript-eslint/explicit-module-boundary-types": "off",
+      "@typescript-eslint/no-extraneous-class": "off",
     },
   },
 ];

packages/shared/eslint.config.js

@@ -0,0 +1,16 @@
+import baseConfig from "@mosaic/config/eslint/base";
+
+export default [
+  ...baseConfig,
+  {
+    languageOptions: {
+      parserOptions: {
+        project: ["./tsconfig.json"],
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+  },
+  {
+    ignores: ["dist/**", "**/*.test.ts", "**/*.spec.ts"],
+  },
+];

packages/shared/src/types/index.ts

@@ -1,38 +1,121 @@
 /**
  * Base entity type with common fields
+ * @invariant updatedAt >= createdAt
  */
 export interface BaseEntity {
-  id: string;
-  createdAt: Date;
+  readonly id: string;
+  readonly createdAt: Date;
   updatedAt: Date;
 }
 
 /**
- * API response wrapper
+ * API response wrapper - discriminated union for type-safe error handling
+ *
+ * Usage:
+ * ```typescript
+ * if (response.success) {
+ *   // TypeScript knows response.data exists
+ *   console.log(response.data);
+ * } else {
+ *   // TypeScript knows response.message exists
+ *   console.error(response.message);
+ * }
+ * ```
  */
-export interface ApiResponse<T> {
-  data: T;
-  success: boolean;
-  message?: string;
+export type ApiResponse<T> =
+  | { success: true; data: T; message?: string }
+  | { success: false; data?: never; message: string; errorCode?: string };
+
+/**
+ * Helper to create a successful API response
+ */
+export function successResponse<T>(data: T, message?: string): ApiResponse<T> {
+  if (message !== undefined) {
+    return { success: true, data, message };
+  }
+  return { success: true, data };
+}
+
+/**
+ * Helper to create an error API response
+ */
+export function errorResponse<T>(message: string, errorCode?: string): ApiResponse<T> {
+  if (errorCode !== undefined) {
+    return { success: false, message, errorCode };
+  }
+  return { success: false, message };
 }
 
 /**
  * Pagination parameters
  */
-export interface PaginationParams {
+export interface PaginationParams<SortableFields extends string = string> {
+  /** Page number (1-indexed) */
   page: number;
+  /** Items per page */
   limit: number;
-  sortBy?: string;
+  /** Field to sort by */
+  sortBy?: SortableFields;
+  /** Sort direction */
   sortOrder?: "asc" | "desc";
 }
 
 /**
  * Paginated response
+ * @invariant totalPages === Math.ceil(total / limit)
+ * @invariant data.length <= limit
+ * @invariant page >= 1 && page <= totalPages (when total > 0)
  */
 export interface PaginatedResponse<T> {
-  data: T[];
-  total: number;
-  page: number;
-  limit: number;
-  totalPages: number;
+  readonly data: readonly T[];
+  readonly total: number;
+  readonly page: number;
+  readonly limit: number;
+  readonly totalPages: number;
+}
+
+/**
+ * Helper to create a paginated response with calculated totalPages
+ */
+export function createPaginatedResponse<T>(
+  data: T[],
+  total: number,
+  page: number,
+  limit: number
+): PaginatedResponse<T> {
+  if (limit <= 0) {
+    throw new Error("limit must be positive");
+  }
+  if (page < 1) {
+    throw new Error("page must be >= 1");
+  }
+
+  return {
+    data,
+    total,
+    page,
+    limit,
+    totalPages: Math.ceil(total / limit) || 1,
+  };
+}
+
+/**
+ * Health check status values
+ */
+export type HealthState = "healthy" | "degraded" | "unhealthy";
+
+/**
+ * Health check response
+ */
+export interface HealthStatus {
+  status: HealthState;
+  timestamp: string;
+  version?: string;
+  checks?: Record<
+    string,
+    {
+      status: HealthState;
+      message?: string;
+    }
+  >;
 }

packages/shared/src/utils/index.test.ts

@@ -35,6 +35,38 @@ describe("slugify", () => {
   it("should trim leading and trailing hyphens", () => {
     expect(slugify("  Hello World  ")).toBe("hello-world");
   });
+
+  it("should handle empty string", () => {
+    expect(slugify("")).toBe("");
+  });
+
+  it("should handle string with only whitespace", () => {
+    expect(slugify("   ")).toBe("");
+  });
+
+  it("should handle consecutive special characters", () => {
+    expect(slugify("Hello---World")).toBe("hello-world");
+    expect(slugify("Hello___World")).toBe("hello-world");
+    expect(slugify("Hello   World")).toBe("hello-world");
+  });
+
+  it("should handle numbers", () => {
+    expect(slugify("Product 123")).toBe("product-123");
+    expect(slugify("2024 New Year")).toBe("2024-new-year");
+  });
+
+  it("should handle mixed case", () => {
+    expect(slugify("HeLLo WoRLd")).toBe("hello-world");
+  });
+
+  it("should remove leading/trailing special chars", () => {
+    expect(slugify("---Hello World---")).toBe("hello-world");
+    expect(slugify("!@#Hello World!@#")).toBe("hello-world");
+  });
+
+  it("should handle string with only special characters", () => {
+    expect(slugify("!@#$%^&*()")).toBe("");
+  });
 });
 
 describe("sleep", () => {

packages/shared/src/utils/index.ts

@@ -1,11 +1,16 @@
 /**
- * Safely parse a date string or return undefined
+ * Safely parse a date string or return undefined.
+ * Logs a warning if an invalid date string is passed.
  */
 export function parseDate(value: string | Date | undefined | null): Date | undefined {
   if (!value) return undefined;
   if (value instanceof Date) return value;
   const parsed = new Date(value);
-  return isNaN(parsed.getTime()) ? undefined : parsed;
+  if (isNaN(parsed.getTime())) {
+    console.warn(`parseDate: Invalid date string received: "${value}"`);
+    return undefined;
+  }
+  return parsed;
 }
 
 /**

packages/ui/eslint.config.js

@@ -0,0 +1,16 @@
+import baseConfig from "@mosaic/config/eslint/base";
+
+export default [
+  ...baseConfig,
+  {
+    languageOptions: {
+      parserOptions: {
+        project: ["./tsconfig.json"],
+        tsconfigRootDir: import.meta.dirname,
+      },
+    },
+  },
+  {
+    ignores: ["dist/**", "**/*.test.tsx", "**/*.test.ts", "**/*.spec.tsx", "**/*.spec.ts"],
+  },
+];

packages/ui/src/components/Button.test.tsx

@@ -1,5 +1,5 @@
-import { describe, expect, it, afterEach } from "vitest";
-import { render, screen, cleanup } from "@testing-library/react";
+import { describe, expect, it, afterEach, vi } from "vitest";
+import { render, screen, cleanup, fireEvent } from "@testing-library/react";
 import { Button } from "./Button.js";
 
 afterEach(() => {
@@ -12,20 +12,75 @@ describe("Button", () => {
     expect(screen.getByRole("button")).toHaveTextContent("Click me");
   });
 
-  it("should apply variant styles", () => {
-    render(<Button variant="danger">Delete</Button>);
-    const button = screen.getByRole("button");
-    expect(button.className).toContain("bg-red-600");
+  describe("variants", () => {
+    it("should apply primary variant styles by default", () => {
+      render(<Button>Primary</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("bg-blue-600");
+    });
+
+    it("should apply secondary variant styles", () => {
+      render(<Button variant="secondary">Secondary</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("bg-gray-200");
+    });
+
+    it("should apply danger variant styles", () => {
+      render(<Button variant="danger">Delete</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("bg-red-600");
+    });
   });
 
-  it("should apply size styles", () => {
-    render(<Button size="lg">Large Button</Button>);
-    const button = screen.getByRole("button");
-    expect(button.className).toContain("px-6");
+  describe("sizes", () => {
+    it("should apply medium size by default", () => {
+      render(<Button>Medium</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("px-4");
+    });
+
+    it("should apply small size styles", () => {
+      render(<Button size="sm">Small</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("px-3");
+    });
+
+    it("should apply large size styles", () => {
+      render(<Button size="lg">Large Button</Button>);
+      const button = screen.getByRole("button");
+      expect(button.className).toContain("px-6");
+    });
+  });
+
+  describe("onClick", () => {
+    it("should call onClick handler when clicked", () => {
+      const handleClick = vi.fn();
+      render(<Button onClick={handleClick}>Click me</Button>);
+      fireEvent.click(screen.getByRole("button"));
+      expect(handleClick).toHaveBeenCalledTimes(1);
+    });
+
+    it("should not call onClick when disabled", () => {
+      const handleClick = vi.fn();
+      render(
+        <Button onClick={handleClick} disabled>
+          Disabled
+        </Button>
+      );
+      fireEvent.click(screen.getByRole("button"));
+      expect(handleClick).not.toHaveBeenCalled();
+    });
   });
 
   it("should pass through additional props", () => {
     render(<Button disabled>Disabled</Button>);
     expect(screen.getByRole("button")).toBeDisabled();
   });
+
+  it("should merge custom className with default styles", () => {
+    render(<Button className="custom-class">Custom</Button>);
+    const button = screen.getByRole("button");
+    expect(button.className).toContain("custom-class");
+    expect(button.className).toContain("bg-blue-600");
+  });
 });