feat(remote): always-on session log to ~/.letta/logs/remote/

Every `letta remote` session now writes a log file to
~/.letta/logs/remote/{timestamp}.log regardless of --debug mode.
All WS events, lifecycle transitions, and errors are captured.
--debug still prints to console on top. Log path printed at startup.
Old logs auto-pruned (keeps last 10).

🐛 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta <noreply@letta.com>

src/websocket/listen-log.ts

@@ -0,0 +1,104 @@
+/**
+ * Always-on file logger for letta remote sessions.
+ * Writes to ~/.letta/logs/remote/{timestamp}.log regardless of --debug mode.
+ * Debug mode additionally prints to console; this file always captures the log.
+ */
+
+import {
+  appendFileSync,
+  existsSync,
+  mkdirSync,
+  readdirSync,
+  unlinkSync,
+} from "node:fs";
+import { homedir } from "node:os";
+import { join } from "node:path";
+
+const REMOTE_LOG_DIR = join(homedir(), ".letta", "logs", "remote");
+const MAX_LOG_FILES = 10;
+
+function formatTimestamp(): string {
+  const now = new Date();
+  const h = String(now.getHours()).padStart(2, "0");
+  const m = String(now.getMinutes()).padStart(2, "0");
+  const s = String(now.getSeconds()).padStart(2, "0");
+  const ms = String(now.getMilliseconds()).padStart(3, "0");
+  return `${h}:${m}:${s}.${ms}`;
+}
+
+function pruneOldLogs(): void {
+  try {
+    if (!existsSync(REMOTE_LOG_DIR)) return;
+    const files = readdirSync(REMOTE_LOG_DIR)
+      .filter((f) => f.endsWith(".log"))
+      .sort();
+    if (files.length >= MAX_LOG_FILES) {
+      const toDelete = files.slice(0, files.length - MAX_LOG_FILES + 1);
+      for (const file of toDelete) {
+        try {
+          unlinkSync(join(REMOTE_LOG_DIR, file));
+        } catch {
+          // best-effort cleanup
+        }
+      }
+    }
+  } catch {
+    // best-effort cleanup
+  }
+}
+
+export class RemoteSessionLog {
+  readonly path: string;
+  private dirCreated = false;
+
+  constructor() {
+    const now = new Date();
+    const stamp = now.toISOString().replace(/[:.]/g, "-");
+    this.path = join(REMOTE_LOG_DIR, `${stamp}.log`);
+  }
+
+  /** Must be called once at startup to create the directory and prune old logs. */
+  init(): void {
+    this.ensureDir();
+    pruneOldLogs();
+  }
+
+  /** Log a line to the file (best-effort, sync). */
+  log(message: string): void {
+    const line = `[${formatTimestamp()}] ${message}\n`;
+    this.appendLine(line);
+  }
+
+  /** Log a WS event in the same format as debugWsLogger. */
+  wsEvent(
+    direction: "send" | "recv",
+    label: "client" | "protocol" | "control" | "lifecycle",
+    event: unknown,
+  ): void {
+    const arrow = direction === "send" ? "\u2192 send" : "\u2190 recv";
+    const tag = label === "client" ? "" : ` (${label})`;
+    const json = JSON.stringify(event);
+    this.log(`${arrow}${tag}  ${json}`);
+  }
+
+  private appendLine(line: string): void {
+    this.ensureDir();
+    try {
+      appendFileSync(this.path, line, { encoding: "utf8" });
+    } catch {
+      // best-effort
+    }
+  }
+
+  private ensureDir(): void {
+    if (this.dirCreated) return;
+    try {
+      if (!existsSync(REMOTE_LOG_DIR)) {
+        mkdirSync(REMOTE_LOG_DIR, { recursive: true });
+      }
+      this.dirCreated = true;
+    } catch {
+      // silently ignore
+    }
+  }
+}