fix(stealth): AGENT_BROWSER_DISABLE_IFRAME_PROXY for a clean 0% CreepJS (issue #4)

--launch mode scored ~20% stealth on CreepJS because the srcdoc-iframe
contentWindow Proxy trips `hasIframeProxy` — the proxy that hides automation is
itself a fingerprintable tell (violates this fork's own "native > JS lies" rule).
Add a config-driven opt-out (no detectable global): AGENT_BROWSER_DISABLE_IFRAME_PROXY=1
drops the patch via __abStealth.disableIframeProxy → the iframe IIFE early-returns
→ clean 0% CreepJS, trading the niche srcdoc-iframe masking. Default keeps current
behavior. README now documents the --launch 20% honestly and scopes the headline
0% to the extension-connect path. Verified: launch + srcdoc page intact with the
toggle; stealth tests green (config strip-prefix kept in sync).

README.md

@@ -225,7 +225,7 @@ When connected to your real Chrome, we inject **zero** JavaScript patches. Your
 
 `0% stealth` on CreepJS is the key number: because the connect path patches **nothing**, there is no override for a lie-detector to catch. (Dashboards that read `navigator.languages` order or IP geolocation may show a soft "navigator"/"location" flag — that tracks *your real Chrome's* language list and network, not an automation tell.)
 
-When using `--launch` mode (standalone browser), a full suite of stealth patches is applied instead, and it still passes the suite above.
+When using `--launch` mode (standalone browser), a full suite of stealth patches is applied instead, and it passes the suite above — with one caveat: CreepJS reports **~20% stealth** because the srcdoc-iframe `contentWindow` patch trips its `hasIframeProxy` probe (the proxy that hides automation is itself a tell). Everything else is clean (`0% headless`, sannysoft/browserscan green, Cloudflare passed). Set **`AGENT_BROWSER_DISABLE_IFRAME_PROXY=1`** to drop that patch for a clean **0% stealth** (trades the niche srcdoc-iframe masking). The **extension-connect path** (your real Chrome) injects zero JS and is unaffected — it's the genuine 0% path.
 
 ### Human-like input (behavioural stealth)
 

cli/src/native/stealth.rs

@@ -51,18 +51,19 @@ pub fn build_stealth_script(mode: StealthMode, locale: Option<&str>) -> String {
         vec![locale, base_lang]
     };
     let config_line = format!(
-        r#"const __abStealth = {{ locale: "{}", languages: {}, allowWebGLContextFallback: false, hideCanvas: {}, canvasSeed: {} }};"#,
+        r#"const __abStealth = {{ locale: "{}", languages: {}, allowWebGLContextFallback: false, hideCanvas: {}, canvasSeed: {}, disableIframeProxy: {} }};"#,
         locale,
         serde_json::to_string(&languages).unwrap_or_else(|_| r#"["en-US","en"]"#.to_string()),
         hide_canvas_enabled(),
         canvas_noise_seed(),
+        disable_iframe_proxy_enabled(),
     );
 
     // NB: this prefix MUST match the first line of stealth_scripts.js verbatim,
     // otherwise the fallback below prepends a SECOND `const __abStealth`
     // declaration and the whole script dies with a redeclaration SyntaxError.
     if let Some(rest) = STEALTH_SCRIPTS_RAW.strip_prefix(
-        r#"const __abStealth = { locale: "en-US", languages: ["en-US", "en"], allowWebGLContextFallback: false, hideCanvas: false, canvasSeed: 0 };"#,
+        r#"const __abStealth = { locale: "en-US", languages: ["en-US", "en"], allowWebGLContextFallback: false, hideCanvas: false, canvasSeed: 0, disableIframeProxy: false };"#,
     ) {
         format!("{}{}", config_line, rest)
     } else {
@@ -81,6 +82,18 @@ fn hide_canvas_enabled() -> bool {
         .unwrap_or(false)
 }
 
+/// Whether to DROP the srcdoc-iframe `contentWindow` Proxy patch (FullLaunch).
+/// That patch masks automation in srcdoc iframes, but the JS `Proxy` is itself a
+/// fingerprintable tell (CreepJS `hasIframeProxy` → ~20% stealth). Off by default
+/// (keep the patch); `AGENT_BROWSER_DISABLE_IFRAME_PROXY=1` drops it for a clean
+/// 0% CreepJS at the cost of that niche srcdoc-iframe masking.
+fn disable_iframe_proxy_enabled() -> bool {
+    std::env::var("AGENT_BROWSER_DISABLE_IFRAME_PROXY")
+        .ok()
+        .map(|v| v == "1" || v.eq_ignore_ascii_case("true"))
+        .unwrap_or(false)
+}
+
 /// A per-process seed so canvas/audio noise is STABLE within a session (a real
 /// device returns the same hash on repeated reads) but differs from the
 /// headless-stable default. 0 is avoided so the JS can treat it as "unset".

cli/src/native/stealth_scripts.js

@@ -1,4 +1,4 @@
-const __abStealth = { locale: "en-US", languages: ["en-US", "en"], allowWebGLContextFallback: false, hideCanvas: false, canvasSeed: 0 };
+const __abStealth = { locale: "en-US", languages: ["en-US", "en"], allowWebGLContextFallback: false, hideCanvas: false, canvasSeed: 0, disableIframeProxy: false };
 // Redefine a navigator property on its PROTOTYPE (Navigator / WorkerNavigator),
 // the way real Chrome exposes these — as prototype getters, NOT instance own
 // properties. Adding an own property to the `navigator` instance is itself a
@@ -289,6 +289,10 @@ const __abRedefineNavProto = (name, getterImpl) => {
 })();
 (function(){
   if (typeof document === 'undefined' || typeof document.createElement !== 'function') return;
+  // The srcdoc-iframe contentWindow Proxy below is itself a fingerprintable tell
+  // (CreepJS `hasIframeProxy`). Honor the opt-out so callers can trade the niche
+  // srcdoc masking for a clean 0% CreepJS fingerprint.
+  if (typeof __abStealth !== 'undefined' && __abStealth.disableIframeProxy) return;
   const nativeCreateElement = document.createElement.bind(document);
   const nativeSrcdocDescriptor =
     typeof HTMLIFrameElement !== 'undefined'