feat(logger): add @bytelyst/logger shared package

createLogger(config) factory for structured logging across dashboards and services.
- Dev: pretty-prints to stderr/stdout
- Prod: JSON structured output for log ingestion (Loki, Datadog, etc.)
- Exports: createLogger, Logger, LoggerConfig, LogLevel, LogPayload

packages/logger/package.json

@@ -0,0 +1,19 @@
+{
+  "name": "@bytelyst/logger",
+  "version": "0.1.0",
+  "description": "Structured logger factory for Next.js dashboards and Node.js services",
+  "type": "module",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js"
+    }
+  },
+  "main": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "files": ["dist"],
+  "scripts": {
+    "build": "tsc",
+    "test": "vitest run"
+  }
+}

packages/logger/src/index.ts

@@ -0,0 +1,2 @@
+export { createLogger } from "./logger.js";
+export type { Logger, LoggerConfig, LogLevel, LogPayload } from "./types.js";

packages/logger/src/logger.ts

@@ -0,0 +1,83 @@
+import type { LogLevel, LogPayload, LoggerConfig, Logger } from "./types.js";
+
+function formatPayload(
+  service: string,
+  level: LogLevel,
+  message: string,
+  error?: unknown,
+  extra?: Record<string, unknown>,
+): LogPayload {
+  const payload: LogPayload = {
+    level,
+    message,
+    timestamp: new Date().toISOString(),
+    service,
+    ...extra,
+  };
+
+  if (error instanceof Error) {
+    payload.error = error.message;
+    payload.stack = error.stack;
+  } else if (error !== undefined) {
+    payload.error = String(error);
+  }
+
+  return payload;
+}
+
+function emit(payload: LogPayload, isDev: boolean): void {
+  if (isDev) {
+    const { level, message, error: err, stack: _stack, ...rest } = payload;
+    const prefix = `[${level.toUpperCase()}]`;
+    const extras = Object.keys(rest).length > 2 ? ` ${JSON.stringify(rest)}` : "";
+    const errStr = err ? ` — ${err}` : "";
+
+    if (level === "error" || level === "warn") {
+      // eslint-disable-next-line no-console
+      console.error(`${prefix} ${message}${errStr}${extras}`);
+    } else {
+      // eslint-disable-next-line no-console
+      console.log(`${prefix} ${message}${extras}`);
+    }
+  } else {
+    const out = JSON.stringify(payload);
+    if (payload.level === "error" || payload.level === "warn") {
+      process.stderr.write(out + "\n");
+    } else {
+      process.stdout.write(out + "\n");
+    }
+  }
+}
+
+/**
+ * Create a structured logger for a service or dashboard.
+ *
+ * @example
+ * ```ts
+ * import { createLogger } from "@bytelyst/logger";
+ * const log = createLogger({ service: "admin-dashboard" });
+ * log.error("Login failed", error, { userId });
+ * log.info("Seed complete", { containers: 8 });
+ * ```
+ */
+export function createLogger(config: LoggerConfig): Logger {
+  const { service } = config;
+  const isDev = config.isDev ?? process.env.NODE_ENV !== "production";
+
+  return {
+    error(message: string, error?: unknown, extra?: Record<string, unknown>): void {
+      emit(formatPayload(service, "error", message, error, extra), isDev);
+    },
+    warn(message: string, extra?: Record<string, unknown>): void {
+      emit(formatPayload(service, "warn", message, undefined, extra), isDev);
+    },
+    info(message: string, extra?: Record<string, unknown>): void {
+      emit(formatPayload(service, "info", message, undefined, extra), isDev);
+    },
+    debug(message: string, extra?: Record<string, unknown>): void {
+      if (isDev) {
+        emit(formatPayload(service, "debug", message, undefined, extra), isDev);
+      }
+    },
+  };
+}

packages/logger/src/types.ts

@@ -0,0 +1,25 @@
+export type LogLevel = "info" | "warn" | "error" | "debug";
+
+export interface LogPayload {
+  level: LogLevel;
+  message: string;
+  timestamp: string;
+  service: string;
+  error?: string;
+  stack?: string;
+  [key: string]: unknown;
+}
+
+export interface LoggerConfig {
+  /** Service name included in every log entry (e.g. "admin-dashboard", "billing-service") */
+  service: string;
+  /** Override NODE_ENV detection for dev/prod mode. Default: reads process.env.NODE_ENV */
+  isDev?: boolean;
+}
+
+export interface Logger {
+  error(message: string, error?: unknown, extra?: Record<string, unknown>): void;
+  warn(message: string, extra?: Record<string, unknown>): void;
+  info(message: string, extra?: Record<string, unknown>): void;
+  debug(message: string, extra?: Record<string, unknown>): void;
+}

packages/logger/tsconfig.json

@@ -0,0 +1,8 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "dist",
+    "rootDir": "src"
+  },
+  "include": ["src"]
+}