fix: deduplicate CLI flags when user args overlap with stealth defaults

Bump version to 0.3.9. Extract shared buildArgs into js/src/args.ts (DRY),
guard console.debug behind DEBUG=cloakbrowser env var, strengthen caplog assertion.

CHANGELOG.md

@@ -6,6 +6,14 @@ Changes are tagged: **[wrapper]** for Python/JS wrapper, **[binary]** for Chromi
 
 ---
 
+## [0.3.9] — 2026-03-05
+
+- **[binary]** Upgrade Chromium base to 145.0.7632.159 (Linux x64). macOS and Windows remain on 145.0.7632.109.2
+- **[binary]** WebGPU adapter spoofing for headless/Docker, timezone multi-context fix, stealth audit phase 2 (6 detection vector fixes), font auto-hide for cross-platform fingerprints
+- **[wrapper]** Default Playwright backend switched from `patchright` to stock `playwright`. Patchright broke proxy auth and `add_init_script` (#27) and is redundant since the binary handles stealth at C++ level. Opt in with `launch(backend="patchright")` or `CLOAKBROWSER_BACKEND=patchright` env var. Install: `pip install cloakbrowser[patchright]`
+- **[wrapper]** Deduplicate CLI flags when user args overlap with stealth defaults — user values win cleanly instead of passing both to Chromium
+- **[wrapper]** Extract shared `buildArgs` into `js/src/args.ts` (JS DRY fix), guard debug logging behind `DEBUG=cloakbrowser` env var
+
 ## [0.3.7] — 2026-03-05
 
 - **[wrapper]** Unify timezone parameter: rename `timezone_id` to `timezone` in `launch_context()`, `launch_persistent_context()`, and `launch_persistent_context_async()` (Python). Old `timezone_id` still works with a deprecation warning. JS: deprecate `timezoneId` on `LaunchContextOptions` — use `timezone` (inherited from `LaunchOptions`)

README.md

@@ -108,7 +108,7 @@ page.goto("https://example.com")
 
 > ⭐ **Star** to show support — **[Watch releases](https://github.com/CloakHQ/CloakBrowser/subscription)** to get notified when new builds drop.
 
-## Latest: v0.3.5 (Chromium 145.0.7632.109)
+## Latest: v0.3.8 (Chromium 145.0.7632.159)
 
 - **All 4 platforms** — Linux x64, macOS arm64, macOS x64, and Windows x64 all on Chromium 145
 - **26 fingerprint patches** — 10 new patches since v142 (screen, device memory, audio, WebGL, auto-spoof, and more)
@@ -125,7 +125,7 @@ See the full [CHANGELOG.md](CHANGELOG.md) for details.
 
 - **Config-level patches break** — `playwright-stealth`, `undetected-chromedriver`, and `puppeteer-extra` inject JavaScript or tweak flags. Every Chrome update breaks them. Antibot systems detect the patches themselves.
 - **CloakBrowser patches Chromium source code** — fingerprints are modified at the C++ level, compiled into the binary. Detection sites see a real browser because it *is* a real browser.
-- **Two layers of stealth** — C++ patches handle fingerprints (GPU, screen, UA, hardware reporting), while the Patchright driver defers Playwright's binding registration and randomizes internal world names. Most stealth tools only do one or the other.
+- **Source-level stealth** — C++ patches handle fingerprints (GPU, screen, UA, hardware reporting) at the binary level. No JavaScript injection, no config-level hacks. Most stealth tools only patch at the surface.
 - **Same behavior everywhere** — works identically local, in Docker, and on VPS. No environment-specific patches or config needed.
 - **Works with any browser automation framework** — tested and passing stealth checks with Playwright, Puppeteer, Selenium, undetected-chromedriver, browser-use, Crawl4AI, and agent-browser. Just point any Chromium-based framework at the binary path.
 
@@ -307,7 +307,7 @@ from cloakbrowser import binary_info, clear_cache, ensure_binary
 
 # Check binary installation status
 print(binary_info())
-# {'version': '145.0.7632.109', 'platform': 'linux-x64', 'installed': True, ...}
+# {'version': '145.0.7632.159', 'platform': 'linux-x64', 'installed': True, ...}
 
 # Force re-download
 clear_cache()
@@ -630,13 +630,13 @@ export CLOAKBROWSER_BINARY_PATH=/path/to/your/chrome
 When auto-update downloads a newer binary, the previous version stays in `~/.cloakbrowser/`. Point `CLOAKBROWSER_BINARY_PATH` to the older cached binary:
 ```bash
 # Linux
-export CLOAKBROWSER_BINARY_PATH=~/.cloakbrowser/chromium-145.0.7632.109/chrome
+export CLOAKBROWSER_BINARY_PATH=~/.cloakbrowser/chromium-145.0.7632.159/chrome
 
 # macOS
-export CLOAKBROWSER_BINARY_PATH=~/.cloakbrowser/chromium-145.0.7632.109/Chromium.app/Contents/MacOS/Chromium
+export CLOAKBROWSER_BINARY_PATH=~/.cloakbrowser/chromium-145.0.7632.109.2/Chromium.app/Contents/MacOS/Chromium
 
 # Windows
-set CLOAKBROWSER_BINARY_PATH=%USERPROFILE%\.cloakbrowser\chromium-145.0.7632.109\chrome.exe
+set CLOAKBROWSER_BINARY_PATH=%USERPROFILE%\.cloakbrowser\chromium-145.0.7632.109.2\chrome.exe
 ```
 
 **macOS: "App is damaged" or Gatekeeper blocks launch**
@@ -648,7 +648,7 @@ xattr -cr ~/.cloakbrowser/chromium-*/Chromium.app
 **"playwright install" vs CloakBrowser binary**
 You do NOT need `playwright install chromium`. CloakBrowser downloads its own binary. You only need Playwright's system deps:
 ```bash
-patchright install-deps chromium
+playwright install-deps chromium
 ```
 
 **macOS: Blocked on some sites that pass on Linux**
@@ -699,6 +699,7 @@ await new Promise(r => setTimeout(r, 3000));
 ```
 
 Other tips for maximizing reCAPTCHA scores:
+- **Try the Patchright backend** — suppresses CDP automation signals that reCAPTCHA Enterprise detects. Install with `pip install cloakbrowser[patchright]`, then use `launch(backend="patchright")` or set `CLOAKBROWSER_BACKEND=patchright` globally. Note: Patchright breaks proxy auth and `add_init_script` — only use it when you need the extra CDP stealth
 - **Use Playwright, not Puppeteer** — Puppeteer sends more CDP protocol traffic that reCAPTCHA detects ([details](#puppeteer))
 - **Use residential proxies** — datacenter IPs are flagged by IP reputation, not browser fingerprint
 - **Spend 15+ seconds on the page** before triggering reCAPTCHA — short visits score lower

cloakbrowser/_version.py

@@ -1 +1 @@
-__version__ = "0.3.8"
+__version__ = "0.3.9"

cloakbrowser/browser.py

@@ -57,6 +57,7 @@ def launch(
     timezone: str | None = None,
     locale: str | None = None,
     geoip: bool = False,
+    backend: str | None = None,
     **kwargs: Any,
 ) -> Any:
     """Launch stealth Chromium browser. Returns a Playwright Browser object.
@@ -76,6 +77,10 @@ def launch(
             Requires ``pip install cloakbrowser[geoip]``. Downloads ~70 MB
             GeoLite2-City database on first use.  Explicit timezone/locale
             always override geoip results.
+        backend: Playwright backend — 'playwright' (default) or 'patchright'.
+            Patchright suppresses CDP signals (helps reCAPTCHA v3 Enterprise)
+            but breaks proxy auth and add_init_script.
+            Override globally with CLOAKBROWSER_BACKEND env var.
         **kwargs: Passed directly to playwright.chromium.launch().
 
     Returns:
@@ -89,7 +94,7 @@ def launch(
         >>> print(page.title())
         >>> browser.close()
     """
-    from patchright.sync_api import sync_playwright
+    sync_playwright = _import_sync_playwright(_resolve_backend(backend))
 
     binary_path = ensure_binary()
     timezone, locale = _maybe_resolve_geoip(geoip, proxy, timezone, locale)
@@ -127,6 +132,7 @@ async def launch_async(
     timezone: str | None = None,
     locale: str | None = None,
     geoip: bool = False,
+    backend: str | None = None,
     **kwargs: Any,
 ) -> Any:
     """Async version of launch(). Returns a Playwright Browser object.
@@ -139,6 +145,7 @@ async def launch_async(
         timezone: IANA timezone (e.g. 'America/New_York'). Sets --fingerprint-timezone binary flag.
         locale: BCP 47 locale (e.g. 'en-US'). Sets --lang binary flag.
         geoip: Auto-detect timezone/locale from proxy IP (default False).
+        backend: Playwright backend — 'playwright' (default) or 'patchright'.
         **kwargs: Passed directly to playwright.chromium.launch().
 
     Returns:
@@ -157,7 +164,7 @@ async def launch_async(
         >>>
         >>> asyncio.run(main())
     """
-    from patchright.async_api import async_playwright
+    async_playwright = _import_async_playwright(_resolve_backend(backend))
 
     binary_path = ensure_binary()
     timezone, locale = _maybe_resolve_geoip(geoip, proxy, timezone, locale)
@@ -199,6 +206,7 @@ def launch_persistent_context(
     timezone: str | None = None,
     color_scheme: Literal["light", "dark", "no-preference"] | None = None,
     geoip: bool = False,
+    backend: str | None = None,
     **kwargs: Any,
 ) -> Any:
     """Launch stealth browser with a persistent profile and return a BrowserContext.
@@ -223,6 +231,7 @@ def launch_persistent_context(
             Default: None (uses Chromium default, which is 'light').
         geoip: Auto-detect timezone/locale from proxy IP (default False).
             Requires ``pip install cloakbrowser[geoip]``.
+        backend: Playwright backend — 'playwright' (default) or 'patchright'.
         **kwargs: Passed directly to playwright.chromium.launch_persistent_context().
 
     Returns:
@@ -236,7 +245,7 @@ def launch_persistent_context(
         >>> page.goto("https://protected-site.com")
         >>> ctx.close()  # Profile is saved; re-use path next run to restore state.
     """
-    from patchright.sync_api import sync_playwright
+    sync_playwright = _import_sync_playwright(_resolve_backend(backend))
 
     timezone = _migrate_timezone_id(timezone, kwargs)
 
@@ -297,6 +306,7 @@ async def launch_persistent_context_async(
     timezone: str | None = None,
     color_scheme: Literal["light", "dark", "no-preference"] | None = None,
     geoip: bool = False,
+    backend: str | None = None,
     **kwargs: Any,
 ) -> Any:
     """Async version of launch_persistent_context().
@@ -318,6 +328,7 @@ async def launch_persistent_context_async(
         timezone: IANA timezone (e.g. 'America/New_York').
         color_scheme: Color scheme preference — 'light', 'dark', or 'no-preference'.
         geoip: Auto-detect timezone/locale from proxy IP (default False).
+        backend: Playwright backend — 'playwright' (default) or 'patchright'.
         **kwargs: Passed directly to playwright.chromium.launch_persistent_context().
 
     Returns:
@@ -336,7 +347,7 @@ async def launch_persistent_context_async(
         >>>
         >>> asyncio.run(main())
     """
-    from patchright.async_api import async_playwright
+    async_playwright = _import_async_playwright(_resolve_backend(backend))
 
     timezone = _migrate_timezone_id(timezone, kwargs)
 
@@ -396,6 +407,7 @@ def launch_context(
     timezone: str | None = None,
     color_scheme: Literal["light", "dark", "no-preference"] | None = None,
     geoip: bool = False,
+    backend: str | None = None,
     **kwargs: Any,
 ) -> Any:
     """Launch stealth browser and return a BrowserContext with common options pre-set.
@@ -414,8 +426,8 @@ def launch_context(
         timezone: IANA timezone (e.g. 'America/New_York').
         color_scheme: Color scheme preference — 'light', 'dark', or 'no-preference'.
             Default: None (uses Chromium default, which is 'light').
-            Note: 'no-preference' doesn't work in Patchright (falls back to 'light').
         geoip: Auto-detect timezone/locale from proxy IP (default False).
+        backend: Playwright backend — 'playwright' (default) or 'patchright'.
         **kwargs: Passed to browser.new_context().
 
     Returns:
@@ -430,7 +442,7 @@ def launch_context(
     # context and interferes with Playwright's timezone_id on new contexts.
     # Timezone is set via browser.new_context(timezone_id=...) below instead.
     browser = launch(headless=headless, proxy=proxy, args=args, stealth_args=stealth_args,
-                     timezone=None, locale=locale)
+                     timezone=None, locale=locale, backend=backend)
 
     context_kwargs: dict[str, Any] = {}
     if user_agent:
@@ -462,6 +474,47 @@ def launch_context(
     return context
 
 
+# ---------------------------------------------------------------------------
+# Backend resolution
+# ---------------------------------------------------------------------------
+
+
+def _resolve_backend(backend: str | None) -> str:
+    """Resolve backend: param > env var > default ('playwright')."""
+    b = backend or os.environ.get("CLOAKBROWSER_BACKEND", "playwright")
+    if b not in ("playwright", "patchright"):
+        raise ValueError(f"Unknown backend '{b}'. Use 'playwright' or 'patchright'.")
+    return b
+
+
+def _import_sync_playwright(backend: str):
+    """Import sync_playwright from the resolved backend."""
+    if backend == "patchright":
+        try:
+            from patchright.sync_api import sync_playwright
+        except ModuleNotFoundError:
+            raise ModuleNotFoundError(
+                "patchright is not installed. Install it with: pip install cloakbrowser[patchright]"
+            ) from None
+        return sync_playwright
+    from playwright.sync_api import sync_playwright
+    return sync_playwright
+
+
+def _import_async_playwright(backend: str):
+    """Import async_playwright from the resolved backend."""
+    if backend == "patchright":
+        try:
+            from patchright.async_api import async_playwright
+        except ModuleNotFoundError:
+            raise ModuleNotFoundError(
+                "patchright is not installed. Install it with: pip install cloakbrowser[patchright]"
+            ) from None
+        return async_playwright
+    from playwright.async_api import async_playwright
+    return async_playwright
+
+
 # ---------------------------------------------------------------------------
 # Internal helpers
 # ---------------------------------------------------------------------------
@@ -496,18 +549,39 @@ def _build_args(
     timezone: str | None = None,
     locale: str | None = None,
 ) -> list[str]:
-    """Combine stealth args with user-provided args and locale flags."""
+    """Combine stealth args with user-provided args and locale flags.
-    result = []
+
+    Deduplicates by flag key (everything before '=').
+    Priority: stealth defaults < user args < dedicated params (timezone/locale).
+    """
+    seen: dict[str, str] = {}
+
     if stealth_args:
-        result.extend(get_default_stealth_args())
+        for arg in get_default_stealth_args():
+            seen[arg.split("=", 1)[0]] = arg
+
     if extra_args:
-        result.extend(extra_args)
+        for arg in extra_args:
+            key = arg.split("=", 1)[0]
+            if key in seen:
+                logger.debug("Arg override: %s -> %s", seen[key], arg)
+            seen[key] = arg
+
     # Timezone/locale flags are independent of stealth_args — always inject when set
     if timezone:
-        result.append(f"--fingerprint-timezone={timezone}")
+        key = "--fingerprint-timezone"
+        flag = f"{key}={timezone}"
+        if key in seen:
+            logger.debug("Arg override: %s -> %s", seen[key], flag)
+        seen[key] = flag
     if locale:
-        result.append(f"--lang={locale}")
+        key = "--lang"
-    return result
+        flag = f"{key}={locale}"
+        if key in seen:
+            logger.debug("Arg override: %s -> %s", seen[key], flag)
+        seen[key] = flag
+
+    return list(seen.values())
 
 
 def _parse_proxy_url(proxy: str) -> dict[str, Any]:

cloakbrowser/config.py

@@ -15,10 +15,10 @@ from ._version import __version__
 # CHROMIUM_VERSION is the latest across all platforms (for display/reference).
 # Use get_chromium_version() for the current platform's actual version.
 # ---------------------------------------------------------------------------
-CHROMIUM_VERSION = "145.0.7632.109.2"
+CHROMIUM_VERSION = "145.0.7632.159"
 
 PLATFORM_CHROMIUM_VERSIONS: dict[str, str] = {
-    "linux-x64": "145.0.7632.109.2",
+    "linux-x64": "145.0.7632.159",
     "darwin-arm64": "145.0.7632.109.2",
     "darwin-x64": "145.0.7632.109.2",
     "windows-x64": "145.0.7632.109.2",

cloakbrowser/download.py

@@ -44,7 +44,7 @@ from .config import (
 logger = logging.getLogger("cloakbrowser")
 
 # Timeout for download (large binary, allow 10 min)
-DOWNLOAD_TIMEOUT = 600.0
+DOWNLOAD_TIMEOUT = httpx.Timeout(connect=10.0, read=60.0, write=10.0, pool=10.0)
 
 # Auto-update check interval (1 hour)
 UPDATE_CHECK_INTERVAL = 3600

js/README.md

@@ -247,13 +247,13 @@ Other tips for maximizing reCAPTCHA scores:
 When auto-update downloads a newer binary, the previous version stays in `~/.cloakbrowser/`. Point `CLOAKBROWSER_BINARY_PATH` to the older cached binary:
 ```bash
 # Linux
-export CLOAKBROWSER_BINARY_PATH=~/.cloakbrowser/chromium-145.0.7632.109/chrome
+export CLOAKBROWSER_BINARY_PATH=~/.cloakbrowser/chromium-145.0.7632.159/chrome
 
 # macOS
-export CLOAKBROWSER_BINARY_PATH=~/.cloakbrowser/chromium-145.0.7632.109/Chromium.app/Contents/MacOS/Chromium
+export CLOAKBROWSER_BINARY_PATH=~/.cloakbrowser/chromium-145.0.7632.109.2/Chromium.app/Contents/MacOS/Chromium
 
 # Windows
-set CLOAKBROWSER_BINARY_PATH=%USERPROFILE%\.cloakbrowser\chromium-145.0.7632.109\chrome.exe
+set CLOAKBROWSER_BINARY_PATH=%USERPROFILE%\.cloakbrowser\chromium-145.0.7632.109.2\chrome.exe
 ```
 
 ## Links

js/package.json

@@ -1,6 +1,6 @@
 {
   "name": "cloakbrowser",
-  "version": "0.3.8",
+  "version": "0.3.9",
   "description": "Stealth Chromium that passes every bot detection test. Drop-in Playwright/Puppeteer replacement with source-level fingerprint patches.",
   "type": "module",
   "main": "dist/index.js",

js/src/args.ts

@@ -0,0 +1,49 @@
+/**
+ * Shared argument builder for Playwright and Puppeteer wrappers.
+ */
+
+import type { LaunchOptions } from "./types.js";
+import { getDefaultStealthArgs } from "./config.js";
+
+const DEBUG = /\bcloakbrowser\b/.test(process.env.DEBUG ?? "");
+
+/**
+ * Build deduplicated Chromium CLI args from stealth defaults + user overrides.
+ *
+ * Priority: stealth defaults < user args < dedicated params (timezone/locale).
+ */
+export function buildArgs(options: LaunchOptions): string[] {
+  const seen = new Map<string, string>();
+
+  if (options.stealthArgs !== false) {
+    for (const arg of getDefaultStealthArgs()) {
+      seen.set(arg.split("=")[0], arg);
+    }
+  }
+  if (options.args) {
+    for (const arg of options.args) {
+      const key = arg.split("=")[0];
+      if (seen.has(key)) {
+        if (DEBUG) console.debug(`[cloakbrowser] Arg override: ${seen.get(key)} -> ${arg}`);
+      }
+      seen.set(key, arg);
+    }
+  }
+  if (options.timezone) {
+    const key = "--fingerprint-timezone";
+    const flag = `${key}=${options.timezone}`;
+    if (seen.has(key)) {
+      if (DEBUG) console.debug(`[cloakbrowser] Arg override: ${seen.get(key)} -> ${flag}`);
+    }
+    seen.set(key, flag);
+  }
+  if (options.locale) {
+    const key = "--lang";
+    const flag = `${key}=${options.locale}`;
+    if (seen.has(key)) {
+      if (DEBUG) console.debug(`[cloakbrowser] Arg override: ${seen.get(key)} -> ${flag}`);
+    }
+    seen.set(key, flag);
+  }
+  return [...seen.values()];
+}

js/src/config.ts

@@ -27,10 +27,10 @@ export { WRAPPER_VERSION };
 // CHROMIUM_VERSION is the latest across all platforms (for display/reference).
 // Use getChromiumVersion() for the current platform's actual version.
 // ---------------------------------------------------------------------------
-export const CHROMIUM_VERSION = "145.0.7632.109.2";
+export const CHROMIUM_VERSION = "145.0.7632.159";
 
 export const PLATFORM_CHROMIUM_VERSIONS: Record<string, string> = {
-  "linux-x64": "145.0.7632.109.2",
+  "linux-x64": "145.0.7632.159",
   "darwin-arm64": "145.0.7632.109.2",
   "darwin-x64": "145.0.7632.109.2",
   "windows-x64": "145.0.7632.109.2",

js/src/playwright.ts

@@ -5,7 +5,8 @@
 
 import type { Browser, BrowserContext } from "playwright-core";
 import type { LaunchOptions, LaunchContextOptions, LaunchPersistentContextOptions } from "./types.js";
-import { DEFAULT_VIEWPORT, getDefaultStealthArgs } from "./config.js";
+import { DEFAULT_VIEWPORT } from "./config.js";
+import { buildArgs } from "./args.js";
 import { ensureBinary } from "./download.js";
 import { parseProxyUrl } from "./proxy.js";
 
@@ -176,24 +177,4 @@ async function maybeResolveGeoip(
 }
 
 /** @internal Exposed for unit tests only. */
-export function _buildArgsForTest(options: LaunchOptions): string[] {
+export { buildArgs as _buildArgsForTest } from "./args.js";
-  return buildArgs(options);
-}
-
-function buildArgs(options: LaunchOptions): string[] {
-  const args: string[] = [];
-  if (options.stealthArgs !== false) {
-    args.push(...getDefaultStealthArgs());
-  }
-  if (options.args) {
-    args.push(...options.args);
-  }
-  // Timezone/locale flags — always inject when set
-  if (options.timezone) {
-    args.push(`--fingerprint-timezone=${options.timezone}`);
-  }
-  if (options.locale) {
-    args.push(`--lang=${options.locale}`);
-  }
-  return args;
-}

js/src/puppeteer.ts

@@ -5,7 +5,7 @@
 
 import type { Browser } from "puppeteer-core";
 import type { LaunchOptions } from "./types.js";
-import { getDefaultStealthArgs } from "./config.js";
+import { buildArgs } from "./args.js";
 import { ensureBinary } from "./download.js";
 import { parseProxyUrl } from "./proxy.js";
 
@@ -99,19 +99,3 @@ async function maybeResolveGeoip(
   };
 }
 
-function buildArgs(options: LaunchOptions): string[] {
-  const args: string[] = [];
-  if (options.stealthArgs !== false) {
-    args.push(...getDefaultStealthArgs());
-  }
-  if (options.args) {
-    args.push(...options.args);
-  }
-  if (options.timezone) {
-    args.push(`--fingerprint-timezone=${options.timezone}`);
-  }
-  if (options.locale) {
-    args.push(`--lang=${options.locale}`);
-  }
-  return args;
-}

js/tests/config.test.ts

@@ -123,6 +123,59 @@ describe("buildArgs timezone/locale", () => {
   });
 });
 
+describe("buildArgs deduplication", () => {
+  it("user --fingerprint overrides default seed", () => {
+    const args = _buildArgsForTest({ args: ["--fingerprint=99887"] });
+    const fpArgs = args.filter(a => a.startsWith("--fingerprint="));
+    expect(fpArgs).toHaveLength(1);
+    expect(fpArgs[0]).toBe("--fingerprint=99887");
+  });
+
+  it("user --fingerprint-platform overrides default", () => {
+    const args = _buildArgsForTest({ args: ["--fingerprint-platform=linux"] });
+    const platArgs = args.filter(a => a.startsWith("--fingerprint-platform="));
+    expect(platArgs).toHaveLength(1);
+    expect(platArgs[0]).toBe("--fingerprint-platform=linux");
+  });
+
+  it("timezone param overrides user --fingerprint-timezone arg", () => {
+    const args = _buildArgsForTest({
+      args: ["--fingerprint-timezone=Europe/London"],
+      timezone: "America/New_York",
+    });
+    const tzArgs = args.filter(a => a.startsWith("--fingerprint-timezone="));
+    expect(tzArgs).toHaveLength(1);
+    expect(tzArgs[0]).toBe("--fingerprint-timezone=America/New_York");
+  });
+
+  it("locale param overrides user --lang arg", () => {
+    const args = _buildArgsForTest({
+      args: ["--lang=de-DE"],
+      locale: "en-US",
+    });
+    const langArgs = args.filter(a => a.startsWith("--lang="));
+    expect(langArgs).toHaveLength(1);
+    expect(langArgs[0]).toBe("--lang=en-US");
+  });
+
+  it("no duplicate flag keys in output", () => {
+    const args = _buildArgsForTest({
+      args: ["--fingerprint=99887", "--fingerprint-timezone=UTC", "--lang=fr-FR"],
+      timezone: "Europe/Berlin",
+      locale: "de-DE",
+    });
+    const keys = args.map(a => a.split("=")[0]);
+    expect(new Set(keys).size).toBe(keys.length);
+  });
+
+  it("non-value flags preserved without dedup issues", () => {
+    const args = _buildArgsForTest({ args: ["--disable-gpu", "--no-zygote"] });
+    expect(args).toContain("--disable-gpu");
+    expect(args).toContain("--no-zygote");
+    expect(args).toContain("--no-sandbox");
+  });
+});
+
 describe("migrateTimezoneId deprecation", () => {
   it("migrates timezoneId to timezone", () => {
     const result = migrateTimezoneId({ timezoneId: "Europe/Paris" });

pyproject.toml

@@ -49,12 +49,13 @@ classifiers = [
     "Topic :: Software Development :: Testing",
 ]
 dependencies = [
-    "patchright>=1.40",
+    "playwright>=1.40",
     "httpx>=0.24",
 ]
 
 [project.optional-dependencies]
 geoip = ["geoip2>=4.0"]
+patchright = ["patchright>=1.40"]
 
 [project.urls]
 Homepage = "https://github.com/CloakHQ/CloakBrowser"

tests/conftest.py

@@ -0,0 +1,11 @@
+"""Shared test fixtures."""
+
+import os
+
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def _clean_backend_env(monkeypatch):
+    """Ensure CLOAKBROWSER_BACKEND doesn't leak into tests from the host environment."""
+    monkeypatch.delenv("CLOAKBROWSER_BACKEND", raising=False)

tests/test_backend.py

@@ -0,0 +1,45 @@
+"""Unit tests for backend resolution (_resolve_backend)."""
+
+import os
+from unittest.mock import patch
+
+import pytest
+
+from cloakbrowser.browser import _resolve_backend
+
+
+def test_resolve_backend_default():
+    """No param, no env var → 'playwright'."""
+    with patch.dict(os.environ, {}, clear=True):
+        assert _resolve_backend(None) == "playwright"
+
+
+def test_resolve_backend_explicit_playwright():
+    assert _resolve_backend("playwright") == "playwright"
+
+
+def test_resolve_backend_explicit_patchright():
+    assert _resolve_backend("patchright") == "patchright"
+
+
+def test_resolve_backend_env_var():
+    """CLOAKBROWSER_BACKEND env var used when no param."""
+    with patch.dict(os.environ, {"CLOAKBROWSER_BACKEND": "patchright"}):
+        assert _resolve_backend(None) == "patchright"
+
+
+def test_resolve_backend_param_beats_env():
+    """Explicit param overrides env var."""
+    with patch.dict(os.environ, {"CLOAKBROWSER_BACKEND": "patchright"}):
+        assert _resolve_backend("playwright") == "playwright"
+
+
+def test_resolve_backend_invalid_raises():
+    with pytest.raises(ValueError, match="Unknown backend 'bogus'"):
+        _resolve_backend("bogus")
+
+
+def test_resolve_backend_invalid_env_raises():
+    with patch.dict(os.environ, {"CLOAKBROWSER_BACKEND": "bogus"}):
+        with pytest.raises(ValueError, match="Unknown backend 'bogus'"):
+            _resolve_backend(None)

tests/test_build_args.py

@@ -92,3 +92,75 @@ def test_migrate_both_none():
         result = _migrate_timezone_id(None, kwargs)
     assert result is None
     assert len(w) == 0
+
+
+# --- Deduplication tests ---
+
+
+def test_user_fingerprint_overrides_default():
+    """User --fingerprint should override the random default seed."""
+    args = _build_args(stealth_args=True, extra_args=["--fingerprint=99887"])
+    fingerprint_args = [a for a in args if a.startswith("--fingerprint=")]
+    assert len(fingerprint_args) == 1
+    assert fingerprint_args[0] == "--fingerprint=99887"
+
+
+def test_user_platform_overrides_default():
+    """User --fingerprint-platform should override the default."""
+    args = _build_args(stealth_args=True, extra_args=["--fingerprint-platform=linux"])
+    platform_args = [a for a in args if a.startswith("--fingerprint-platform=")]
+    assert len(platform_args) == 1
+    assert platform_args[0] == "--fingerprint-platform=linux"
+
+
+def test_timezone_param_overrides_user_arg():
+    """Dedicated timezone param should override user arg."""
+    args = _build_args(
+        stealth_args=True,
+        extra_args=["--fingerprint-timezone=Europe/London"],
+        timezone="America/New_York",
+    )
+    tz_args = [a for a in args if a.startswith("--fingerprint-timezone=")]
+    assert len(tz_args) == 1
+    assert tz_args[0] == "--fingerprint-timezone=America/New_York"
+
+
+def test_locale_param_overrides_user_arg():
+    """Dedicated locale param should override user --lang arg."""
+    args = _build_args(
+        stealth_args=True,
+        extra_args=["--lang=de-DE"],
+        locale="en-US",
+    )
+    lang_args = [a for a in args if a.startswith("--lang=")]
+    assert len(lang_args) == 1
+    assert lang_args[0] == "--lang=en-US"
+
+
+def test_no_duplicate_flags():
+    """No flag key should appear more than once in the output."""
+    args = _build_args(
+        stealth_args=True,
+        extra_args=["--fingerprint=99887", "--fingerprint-timezone=UTC", "--lang=fr-FR"],
+        timezone="Europe/Berlin",
+        locale="de-DE",
+    )
+    keys = [a.split("=", 1)[0] for a in args]
+    assert len(keys) == len(set(keys)), f"Duplicate keys found: {keys}"
+
+
+def test_non_value_flags_preserved():
+    """Flags without = should be preserved without dedup issues."""
+    args = _build_args(stealth_args=True, extra_args=["--disable-gpu", "--no-zygote"])
+    assert "--disable-gpu" in args
+    assert "--no-zygote" in args
+    assert "--no-sandbox" in args
+
+
+def test_override_logs_debug(caplog):
+    """Should log debug message when an override happens."""
+    import logging
+
+    with caplog.at_level(logging.DEBUG, logger="cloakbrowser"):
+        _build_args(stealth_args=True, extra_args=["--fingerprint=99887"])
+    assert any("--fingerprint=" in r.message and "99887" in r.message for r in caplog.records)

tests/test_persistent_context.py

@@ -1,6 +1,6 @@
 """Unit tests for launch_persistent_context() and launch_persistent_context_async().
 
-All tests mock patchright to avoid needing a binary.
+All tests mock playwright to avoid needing a binary.
 """
 
 import warnings
@@ -32,7 +32,7 @@ def test_persistent_context_args_built(_mock_geoip, _mock_bin):
     """Stealth args + extra args combined correctly."""
     pw_cm, pw, context = _make_mock_pw_and_context()
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         launch_persistent_context("/tmp/profile", args=["--disable-gpu"])
 
@@ -48,7 +48,7 @@ def test_persistent_context_default_viewport(_mock_geoip, _mock_bin):
     """DEFAULT_VIEWPORT applied when no viewport given."""
     pw_cm, pw, context = _make_mock_pw_and_context()
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         launch_persistent_context("/tmp/profile")
 
@@ -63,7 +63,7 @@ def test_persistent_context_custom_viewport(_mock_geoip, _mock_bin):
     pw_cm, pw, context = _make_mock_pw_and_context()
     custom = {"width": 1280, "height": 720}
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         launch_persistent_context("/tmp/profile", viewport=custom)
 
@@ -77,7 +77,7 @@ def test_persistent_context_user_agent(_mock_geoip, _mock_bin):
     """user_agent forwarded to launch_persistent_context()."""
     pw_cm, pw, context = _make_mock_pw_and_context()
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         launch_persistent_context("/tmp/profile", user_agent="Custom/1.0")
 
@@ -90,7 +90,7 @@ def test_persistent_context_locale_and_timezone(_mock_bin):
     """Both timezone and locale flow to context kwargs and binary args."""
     pw_cm, pw, context = _make_mock_pw_and_context()
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         launch_persistent_context("/tmp/profile", timezone="Asia/Tokyo", locale="ja-JP")
 
@@ -109,7 +109,7 @@ def test_persistent_context_color_scheme(_mock_geoip, _mock_bin):
     """color_scheme forwarded correctly."""
     pw_cm, pw, context = _make_mock_pw_and_context()
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         launch_persistent_context("/tmp/profile", color_scheme="dark")
 
@@ -123,7 +123,7 @@ def test_persistent_context_geoip(_mock_bin, _mock_geoip):
     """geoip fills missing tz/locale."""
     pw_cm, pw, context = _make_mock_pw_and_context()
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         launch_persistent_context("/tmp/profile", proxy="http://proxy:8080", geoip=True)
 
@@ -137,7 +137,7 @@ def test_persistent_context_timezone_id_deprecation(_mock_bin):
     """Old timezone_id kwarg migrated with warning."""
     pw_cm, pw, context = _make_mock_pw_and_context()
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         with warnings.catch_warnings(record=True) as w:
             warnings.simplefilter("always")
@@ -156,7 +156,7 @@ def test_persistent_context_close_stops_pw(_mock_geoip, _mock_bin):
     pw_cm, pw, context = _make_mock_pw_and_context()
     original_close = context.close
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         ctx = launch_persistent_context("/tmp/profile")
 
@@ -171,7 +171,7 @@ def test_persistent_context_proxy_string(_mock_geoip, _mock_bin):
     """Proxy string parsed and passed."""
     pw_cm, pw, context = _make_mock_pw_and_context()
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         launch_persistent_context("/tmp/profile", proxy="http://user:pass@proxy:8080")
 
@@ -188,7 +188,7 @@ def test_persistent_context_proxy_dict(_mock_geoip, _mock_bin):
     pw_cm, pw, context = _make_mock_pw_and_context()
     proxy_dict = {"server": "http://proxy:8080", "bypass": ".google.com"}
 
-    with patch("patchright.sync_api.sync_playwright", return_value=pw_cm):
+    with patch("playwright.sync_api.sync_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context
         launch_persistent_context("/tmp/profile", proxy=proxy_dict)
 
@@ -218,7 +218,7 @@ async def test_persistent_context_async_args_built(_mock_geoip, _mock_bin):
     """Async launch builds args correctly."""
     pw_cm, pw, context = _make_mock_async_pw_and_context()
 
-    with patch("patchright.async_api.async_playwright", return_value=pw_cm):
+    with patch("playwright.async_api.async_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context_async
         await launch_persistent_context_async("/tmp/profile", args=["--disable-gpu"])
 
@@ -235,7 +235,7 @@ async def test_persistent_context_async_close_stops_pw(_mock_geoip, _mock_bin):
     pw_cm, pw, context = _make_mock_async_pw_and_context()
     original_close = context.close
 
-    with patch("patchright.async_api.async_playwright", return_value=pw_cm):
+    with patch("playwright.async_api.async_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context_async
         ctx = await launch_persistent_context_async("/tmp/profile")
 
@@ -250,7 +250,7 @@ async def test_persistent_context_async_timezone_id_deprecation(_mock_bin):
     """Deprecated timezone_id kwarg migrated with warning in async path."""
     pw_cm, pw, context = _make_mock_async_pw_and_context()
 
-    with patch("patchright.async_api.async_playwright", return_value=pw_cm):
+    with patch("playwright.async_api.async_playwright", return_value=pw_cm):
         from cloakbrowser.browser import launch_persistent_context_async
         with warnings.catch_warnings(record=True) as w:
             warnings.simplefilter("always")