feat: add rotating file logger

src/core/logger.ts

@@ -0,0 +1,68 @@
+/**
+ * Rotating file logger. Writes to data/logs/phantom.log.
+ * Rotates to phantom.log.1 when the file exceeds MAX_SIZE_BYTES.
+ * Designed to never throw - logging must not crash the main process.
+ */
+
+import { appendFileSync, existsSync, mkdirSync, renameSync, statSync } from "node:fs";
+import { dirname, resolve } from "node:path";
+
+const MAX_SIZE_BYTES = 10 * 1024 * 1024; // 10 MB
+
+type LogLevel = "ERROR" | "WARN" | "INFO";
+
+export class Logger {
+	private path: string;
+	private ready = false;
+
+	constructor(logPath: string) {
+		this.path = resolve(logPath);
+		try {
+			mkdirSync(dirname(this.path), { recursive: true });
+			this.ready = true;
+		} catch {
+			// Can't create log directory - silently degrade
+		}
+	}
+
+	error(tag: string, message: string): void {
+		this.write("ERROR", tag, message);
+	}
+
+	warn(tag: string, message: string): void {
+		this.write("WARN", tag, message);
+	}
+
+	info(tag: string, message: string): void {
+		this.write("INFO", tag, message);
+	}
+
+	getPath(): string {
+		return this.path;
+	}
+
+	private write(level: LogLevel, tag: string, message: string): void {
+		if (!this.ready) return;
+		try {
+			this.maybeRotate();
+			const line = `${new Date().toISOString()} [${level}] [${tag}] ${message}\n`;
+			appendFileSync(this.path, line, "utf-8");
+		} catch {
+			// Silently degrade
+		}
+	}
+
+	private maybeRotate(): void {
+		try {
+			if (!existsSync(this.path)) return;
+			const { size } = statSync(this.path);
+			if (size >= MAX_SIZE_BYTES) {
+				renameSync(this.path, `${this.path}.1`);
+			}
+		} catch {
+			// Ignore rotation errors
+		}
+	}
+}
+
+export const logger = new Logger("data/logs/phantom.log");

src/index.ts

@@ -16,6 +16,7 @@ import { TelegramChannel } from "./channels/telegram.ts";
 import { WebhookChannel } from "./channels/webhook.ts";
 import { loadChannelsConfig, loadConfig } from "./config/loader.ts";
 import { installShutdownHandlers, onShutdown } from "./core/graceful.ts";
+import { logger } from "./core/logger.ts";
 import {
 	setChannelHealthProvider,
 	setEvolutionVersionProvider,
@@ -53,10 +54,24 @@ import { createSecretToolServer } from "./secrets/tools.ts";
 import { setPublicDir, setSecretSavedCallback, setSecretsDb } from "./ui/serve.ts";
 import { createWebUiToolServer } from "./ui/tools.ts";
 
+// Intercept console.error and console.warn to mirror into the log file.
+// All existing code benefits without needing to import the logger directly.
+const _origError = console.error.bind(console);
+const _origWarn = console.warn.bind(console);
+console.error = (...args: unknown[]) => {
+	_origError(...args);
+	logger.error("console", args.map(String).join(" "));
+};
+console.warn = (...args: unknown[]) => {
+	_origWarn(...args);
+	logger.warn("console", args.map(String).join(" "));
+};
+
 async function main(): Promise<void> {
 	const startedAt = Date.now();
 
 	console.log("[phantom] Starting...");
+	logger.info("phantom", `Starting - log file: ${logger.getPath()}`);
 
 	const config = loadConfig();
 	console.log(`[phantom] Config loaded: ${config.name} (${config.model}, effort: ${config.effort})`);