diff --git a/packages/desktop/src/main/debug/logger.ts b/packages/desktop/src/main/debug/logger.ts
index 474dbf6f..78099b78 100644
--- a/packages/desktop/src/main/debug/logger.ts
+++ b/packages/desktop/src/main/debug/logger.ts
@@ -1,4 +1,14 @@
-import { createWriteStream, existsSync, mkdirSync, openSync, type WriteStream } from 'node:fs';
+import {
+  createWriteStream,
+  existsSync,
+  mkdirSync,
+  openSync,
+  readdirSync,
+  renameSync,
+  statSync,
+  unlinkSync,
+  type WriteStream,
+} from 'node:fs';
 import { join } from 'node:path';
 import type { DebugDomain, DebugEvent, DebugLevel } from '@clawwork/shared';
 import { sanitizeForLog } from '@clawwork/shared';
@@ -8,6 +18,8 @@ interface CreateDebugLoggerOptions {
   maxEvents?: number;
   console?: boolean;
   onEvent?: (event: DebugEvent) => void;
+  maxFileSize?: number;
+  retentionDays?: number;
 }
 
 export interface DebugLogFilter {
@@ -55,40 +67,76 @@ export interface LogEventInput {
 export function createDebugLogger(options: CreateDebugLoggerOptions): DebugLogger {
   const maxEvents = options.maxEvents ?? 1000;
   const writeConsole = options.console ?? true;
+  const maxFileSize = options.maxFileSize ?? 50 * 1024 * 1024;
+  const retentionDays = options.retentionDays ?? 14;
   const recentEvents: DebugEvent[] = [];
   const debugDir = options.debugDir;
 
   // Write stream state — cached fd avoids open/write/close per event
   let writeStream: WriteStream | null = null;
   let currentLogDate = '';
+  let currentFileSize = 0;
 
   ensureDir(debugDir);
 
+  // Age-based cleanup: purge files older than retentionDays
+  if (retentionDays > 0) {
+    cleanupOldLogs(debugDir, retentionDays);
+  }
+
   function currentFilePath(): string {
     const day = new Date().toISOString().slice(0, 10);
     return join(debugDir, `debug-${day}.ndjson`);
   }
 
-  function ensureStream(): void {
+  /** Open a write stream for the current day's file. Restores file size via statSync
+   *  so mid-day process restarts don't lose track of the written size. */
+  function openStream(): void {
     const today = new Date().toISOString().slice(0, 10);
-    if (writeStream && currentLogDate === today) return;
-
-    // Close previous day's stream
-    if (writeStream) {
-      writeStream.end();
-      writeStream = null;
-    }
-
     ensureDir(debugDir);
     currentLogDate = today;
     const filePath = currentFilePath();
-    // Open fd synchronously so the file exists immediately and is append-only
+    // Restore file size on init (handles process restart mid-day)
+    try {
+      currentFileSize = statSync(filePath).size;
+    } catch {
+      currentFileSize = 0;
+    }
     const fd = openSync(filePath, 'a');
     writeStream = createWriteStream(filePath, { fd, autoClose: true }).on('error', (err) => {
       console.error('[debug] logger stream error:', err);
     });
   }
 
+  function ensureStream(): void {
+    const today = new Date().toISOString().slice(0, 10);
+
+    // Same day, stream open — check tracked size for rotation
+    if (writeStream && currentLogDate === today) {
+      if (currentFileSize >= maxFileSize) {
+        // Rotate: close stream, find next slot, rename current file
+        writeStream.end();
+        writeStream = null;
+
+        let rotIdx = 1;
+        while (existsSync(join(debugDir, `debug-${today}.${rotIdx}.ndjson`))) {
+          rotIdx++;
+        }
+        renameSync(currentFilePath(), join(debugDir, `debug-${today}.${rotIdx}.ndjson`));
+        openStream();
+      } else {
+        return; // stream is fine, no rotation needed
+      }
+    } else {
+      // Date changed, first call, or stream was rotated
+      if (writeStream) {
+        writeStream.end();
+        writeStream = null;
+      }
+      openStream();
+    }
+  }
+
   function log(input: LogEventInput & { level: DebugLevel }): DebugEvent {
     const event: DebugEvent = sanitizeForLog({
       ts: new Date().toISOString(),
@@ -102,7 +150,9 @@ export function createDebugLogger(options: CreateDebugLoggerOptions): DebugLogge
 
     // Async write via persistent stream — no more blocking the event loop
     ensureStream();
-    writeStream!.write(`${JSON.stringify(event)}\n`, 'utf8');
+    const jsonLine = `${JSON.stringify(event)}\n`;
+    currentFileSize += Buffer.byteLength(jsonLine, 'utf8');
+    writeStream!.write(jsonLine, 'utf8');
 
     if (writeConsole) {
       const line = `[${event.level}] [${event.domain}] ${event.event}`;
@@ -159,3 +209,17 @@ function ensureDir(dir: string): void {
     mkdirSync(dir, { recursive: true });
   }
 }
+
+function cleanupOldLogs(dir: string, retentionDays: number): void {
+  const cutoff = Date.now() - retentionDays * 24 * 60 * 60 * 1000;
+  const entries = readdirSync(dir, { withFileTypes: true });
+  for (const entry of entries) {
+    if (!entry.isFile()) continue;
+    const match = entry.name.match(/^debug-(\d{4}-\d{2}-\d{2})(?:\.\d+)?\.ndjson$/);
+    if (!match) continue;
+    const fileDate = new Date(match[1]).getTime();
+    if (fileDate < cutoff) {
+      unlinkSync(join(dir, entry.name));
+    }
+  }
+}
diff --git a/packages/desktop/test/debug-logger-rotation.test.ts b/packages/desktop/test/debug-logger-rotation.test.ts
new file mode 100644
index 00000000..f1f4af58
--- /dev/null
+++ b/packages/desktop/test/debug-logger-rotation.test.ts
@@ -0,0 +1,247 @@
+import { describe, expect, it, beforeEach, afterEach } from 'vitest';
+import { mkdtempSync, rmSync, existsSync, readdirSync, writeFileSync, statSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { createDebugLogger } from '../src/main/debug/logger';
+
+describe('debug logger size rotation', () => {
+  let dir: string;
+
+  beforeEach(() => {
+    dir = mkdtempSync(join(tmpdir(), 'clawwork-debug-rotation-'));
+  });
+
+  afterEach(() => {
+    rmSync(dir, { recursive: true, force: true });
+  });
+
+  it('rotates to .1.ndjson when file exceeds maxFileSize', async () => {
+    const logger = createDebugLogger({
+      debugDir: dir,
+      maxEvents: 1000,
+      console: false,
+      maxFileSize: 100, // tiny — rotate after ~100 bytes
+    });
+
+    // Write enough events to trigger rotation
+    for (let i = 0; i < 50; i++) {
+      logger.info({
+        domain: 'gateway',
+        event: `test-event-${i}`,
+        message: 'x'.repeat(40), // each event ~60-100 bytes
+      });
+    }
+
+    await logger.flush();
+
+    const files = readdirSync(dir).filter((f) => f.endsWith('.ndjson'));
+    // Should have at least 2 files (rotated + current)
+    expect(files.length).toBeGreaterThanOrEqual(2);
+
+    // The rotated file should exist
+    const rotatedFiles = files.filter((f) => f.includes('.1.ndjson'));
+    expect(rotatedFiles.length).toBeGreaterThanOrEqual(1);
+
+    // The current (active) file should be under the size limit
+    // current is debug-YYYY-MM-DD.ndjson, rotated are .1, .2, etc.
+    // The "current" active file has no suffix
+    const activeFile = files.find((f) => /^debug-\d{4}-\d{2}-\d{2}\.ndjson$/.test(f) && !/\.\d+\.ndjson$/.test(f));
+    if (activeFile) {
+      const size = statSync(join(dir, activeFile)).size;
+      expect(size).toBeLessThan(200); // well within the limit
+    }
+
+    // Verify rotated files are named correctly
+    for (const f of rotatedFiles) {
+      expect(f).toMatch(/^debug-\d{4}-\d{2}-\d{2}\.\d+\.ndjson$/);
+    }
+  });
+
+  it('creates multiple rotation files .1, .2, .3 when needed', async () => {
+    const logger = createDebugLogger({
+      debugDir: dir,
+      maxEvents: 5000,
+      console: false,
+      maxFileSize: 80, // very tiny — rotate frequently
+    });
+
+    // Write many big events to trigger multiple rotations
+    for (let i = 0; i < 100; i++) {
+      logger.info({
+        domain: 'gateway',
+        event: `big-event-${i}`,
+        message: 'z'.repeat(60),
+      });
+    }
+
+    await logger.flush();
+
+    // Find all rotation files
+    const files = readdirSync(dir).filter((f) => f.endsWith('.ndjson'));
+    const rotNums = files
+      .map((f) => {
+        const m = f.match(/\.(\d+)\.ndjson$/);
+        return m ? parseInt(m[1], 10) : 0;
+      })
+      .filter((n) => n > 0);
+
+    // Expect at least 2 distinct rotation indices
+    expect(rotNums.length).toBeGreaterThanOrEqual(2);
+
+    // The highest rotation index should exist
+    const maxRot = Math.max(...rotNums);
+    expect(existsSync(join(dir, `debug-${new Date().toISOString().slice(0, 10)}.${maxRot}.ndjson`))).toBe(true);
+  });
+});
+
+describe('debug logger retention cleanup', () => {
+  let dir: string;
+
+  beforeEach(() => {
+    dir = mkdtempSync(join(tmpdir(), 'clawwork-debug-retention-'));
+  });
+
+  afterEach(() => {
+    rmSync(dir, { recursive: true, force: true });
+  });
+
+  it('deletes log files older than retentionDays on init', () => {
+    const today = new Date().toISOString().slice(0, 10);
+
+    // Create old log files (15 days ago)
+    const oldDate = new Date(Date.now() - 15 * 24 * 60 * 60 * 1000);
+    const oldDateStr = oldDate.toISOString().slice(0, 10);
+
+    writeFileSync(join(dir, `debug-${oldDateStr}.ndjson`), 'old log data\n');
+    writeFileSync(join(dir, `debug-${oldDateStr}.1.ndjson`), 'old rotated log data\n');
+
+    // Create recent log files (today)
+    writeFileSync(join(dir, `debug-${today}.ndjson`), 'current log data\n');
+
+    // Create unrelated files that should not be touched
+    writeFileSync(join(dir, 'other-file.txt'), 'not a log\n');
+
+    expect(existsSync(join(dir, `debug-${oldDateStr}.ndjson`))).toBe(true);
+    expect(existsSync(join(dir, `debug-${oldDateStr}.1.ndjson`))).toBe(true);
+    expect(existsSync(join(dir, `debug-${today}.ndjson`))).toBe(true);
+
+    // Create logger with 7-day retention — this triggers cleanup
+    createDebugLogger({
+      debugDir: dir,
+      maxEvents: 100,
+      console: false,
+      retentionDays: 7,
+    });
+
+    // Old files should be deleted
+    expect(existsSync(join(dir, `debug-${oldDateStr}.ndjson`))).toBe(false);
+    expect(existsSync(join(dir, `debug-${oldDateStr}.1.ndjson`))).toBe(false);
+
+    // Recent file should remain
+    expect(existsSync(join(dir, `debug-${today}.ndjson`))).toBe(true);
+
+    // Non-log files should be untouched
+    expect(existsSync(join(dir, 'other-file.txt'))).toBe(true);
+  });
+
+  it('does not delete recent files within retentionDays', () => {
+    const today = new Date().toISOString().slice(0, 10);
+
+    // Create file from 3 days ago
+    const recentDate = new Date(Date.now() - 3 * 24 * 60 * 60 * 1000);
+    const recentDateStr = recentDate.toISOString().slice(0, 10);
+
+    writeFileSync(join(dir, `debug-${recentDateStr}.ndjson`), 'recent log\n');
+    writeFileSync(join(dir, `debug-${today}.ndjson`), 'current log\n');
+
+    // Create logger with 7-day retention
+    createDebugLogger({
+      debugDir: dir,
+      maxEvents: 100,
+      console: false,
+      retentionDays: 7,
+    });
+
+    // Both files should survive (3 days < 7 days)
+    expect(existsSync(join(dir, `debug-${recentDateStr}.ndjson`))).toBe(true);
+    expect(existsSync(join(dir, `debug-${today}.ndjson`))).toBe(true);
+  });
+
+  it('disables cleanup when retentionDays is 0', () => {
+    const today = new Date().toISOString().slice(0, 10);
+
+    // Create very old files
+    const oldDate = new Date(Date.now() - 100 * 24 * 60 * 60 * 1000);
+    const oldDateStr = oldDate.toISOString().slice(0, 10);
+
+    writeFileSync(join(dir, `debug-${oldDateStr}.ndjson`), 'very old log\n');
+    writeFileSync(join(dir, `debug-${today}.ndjson`), 'current log\n');
+
+    // Create logger with retentionDays=0 (disabled)
+    createDebugLogger({
+      debugDir: dir,
+      maxEvents: 100,
+      console: false,
+      retentionDays: 0,
+    });
+
+    // Old file should still exist
+    expect(existsSync(join(dir, `debug-${oldDateStr}.ndjson`))).toBe(true);
+    expect(existsSync(join(dir, `debug-${today}.ndjson`))).toBe(true);
+  });
+});
+
+describe('debug logger file size boundaries', () => {
+  let dir: string;
+
+  beforeEach(() => {
+    dir = mkdtempSync(join(tmpdir(), 'clawwork-debug-boundary-'));
+  });
+
+  afterEach(() => {
+    rmSync(dir, { recursive: true, force: true });
+  });
+
+  it('keeps active file within size limit across rotations', async () => {
+    // Create a logger with a moderate size limit
+    const maxFileSize = 500;
+    const logger = createDebugLogger({
+      debugDir: dir,
+      maxEvents: 5000,
+      console: false,
+      maxFileSize,
+    });
+
+    // Write events in batches with flush
+    for (let batch = 0; batch < 5; batch++) {
+      for (let i = 0; i < 10; i++) {
+        logger.info({
+          domain: 'gateway',
+          event: `batch-${batch}-event-${i}`,
+          message: 'a'.repeat(50),
+        });
+      }
+      await logger.flush();
+    }
+
+    await logger.flush();
+
+    // The active file should be well within the size limit
+    const files = readdirSync(dir).filter((f) => f.endsWith('.ndjson'));
+    const activeFile = files.find((f) => /^debug-\d{4}-\d{2}-\d{2}\.ndjson$/.test(f) && !/\.\d+\.ndjson$/.test(f));
+    expect(activeFile).toBeTruthy();
+    const activeSize = statSync(join(dir, activeFile!)).size;
+
+    // Active file should not exceed maxFileSize
+    expect(activeSize).toBeLessThan(maxFileSize);
+
+    // All rotated files should also stay within limits
+    for (const f of files) {
+      if (f === activeFile) continue;
+      const size = statSync(join(dir, f)).size;
+      // Rotated files may exceed maxFileSize slightly since they're renamed when the limit is hit
+      // but they shouldn't be wildly larger
+      expect(size).toBeLessThan(maxFileSize * 2);
+    }
+  });
+});