From d269c87b824a720bf17bb93a2e482d707174c3d9 Mon Sep 17 00:00:00 2001
From: Lukasz Raczylo <lukasz@raczylo.com>
Date: Sun, 7 Jun 2026 13:20:55 +0100
Subject: [PATCH] feat(stealth): embeddable evasion init script with apply
 hints

---
 internal/stealth/assets/evasions.js | 25 +++++++++++++++++
 internal/stealth/script.go          | 43 +++++++++++++++++++++++++++++
 internal/stealth/script_test.go     | 21 ++++++++++++++
 3 files changed, 89 insertions(+)
 create mode 100644 internal/stealth/assets/evasions.js
 create mode 100644 internal/stealth/script.go
 create mode 100644 internal/stealth/script_test.go

diff --git a/internal/stealth/assets/evasions.js b/internal/stealth/assets/evasions.js
new file mode 100644
index 0000000..49f4a9a
--- /dev/null
+++ b/internal/stealth/assets/evasions.js
@@ -0,0 +1,25 @@
+(() => {
+  // navigator.webdriver
+  Object.defineProperty(navigator, 'webdriver', { get: () => undefined });
+  // languages
+  Object.defineProperty(navigator, 'languages', { get: () => ['en-US', 'en'] });
+  // plugins (non-empty)
+  Object.defineProperty(navigator, 'plugins', { get: () => [1, 2, 3, 4, 5] });
+  // chrome runtime stub
+  window.chrome = window.chrome || { runtime: {} };
+  // permissions query consistency
+  const origQuery = window.navigator.permissions && window.navigator.permissions.query;
+  if (origQuery) {
+    window.navigator.permissions.query = (params) =>
+      params && params.name === 'notifications'
+        ? Promise.resolve({ state: Notification.permission })
+        : origQuery(params);
+  }
+  // WebGL vendor/renderer spoof
+  const getParam = WebGLRenderingContext.prototype.getParameter;
+  WebGLRenderingContext.prototype.getParameter = function (p) {
+    if (p === 37445) return 'Google Inc.';        // UNMASKED_VENDOR_WEBGL
+    if (p === 37446) return 'ANGLE (Generic GPU)'; // UNMASKED_RENDERER_WEBGL
+    return getParam.call(this, p);
+  };
+})();
diff --git a/internal/stealth/script.go b/internal/stealth/script.go
new file mode 100644
index 0000000..5b10e3b
--- /dev/null
+++ b/internal/stealth/script.go
@@ -0,0 +1,43 @@
+package stealth
+
+import _ "embed"
+
+//go:embed assets/evasions.js
+var evasionsJS string
+
+// ScriptParams selects the target engine for apply instructions.
+type ScriptParams struct {
+	Engine string // playwright | cdp | generic
+}
+
+// ApplyInfo tells the caller how to inject the script.
+type ApplyInfo struct {
+	How string `json:"how"`
+	API string `json:"api"`
+}
+
+// ScriptResult is the injectable evasion bundle plus metadata.
+type ScriptResult struct {
+	Script           string    `json:"script"`
+	Apply            ApplyInfo `json:"apply"`
+	IncludedEvasions []string  `json:"included_evasions"`
+}
+
+// StealthScript returns the evasion init script and engine-specific apply hints.
+func StealthScript(p ScriptParams) ScriptResult {
+	apply := ApplyInfo{How: "Inject before any page script runs.", API: "page.addInitScript(script)"}
+	switch p.Engine {
+	case "cdp":
+		apply.API = "Page.addScriptToEvaluateOnNewDocument({source: script})"
+	case "generic", "":
+		apply.API = "evaluate the script on every new document before navigation"
+	}
+	return ScriptResult{
+		Script: evasionsJS,
+		Apply:  apply,
+		IncludedEvasions: []string{
+			"navigator.webdriver", "navigator.languages", "navigator.plugins",
+			"chrome.runtime", "permissions.query", "WebGL vendor/renderer",
+		},
+	}
+}
diff --git a/internal/stealth/script_test.go b/internal/stealth/script_test.go
new file mode 100644
index 0000000..2ccf7b9
--- /dev/null
+++ b/internal/stealth/script_test.go
@@ -0,0 +1,21 @@
+package stealth
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestStealthScript(t *testing.T) {
+	res := StealthScript(ScriptParams{Engine: "playwright"})
+	if res.Script == "" {
+		t.Fatal("empty script")
+	}
+	for _, want := range []string{"navigator.webdriver", "languages", "WebGL", "chrome"} {
+		if !strings.Contains(res.Script, want) {
+			t.Fatalf("script missing %q", want)
+		}
+	}
+	if res.Apply.How == "" || len(res.IncludedEvasions) == 0 {
+		t.Fatalf("missing apply metadata: %+v", res)
+	}
+}