fix: remove WebMessageListener before destroying WebView to prevent memory leaks

Adds defensive cleanup in destroyWebView() by removing the native bridge
binding prior to webView.destroy(). Uses WebViewCompat.removeWebMessageListener
when supported, falling back to removeJavascriptInterface for older WebView
implementations. This addresses a reported memory leak where
WebMessageListenerHolder retains KlaviyoWebView on some vendor implementations.

Closes #430 | Part of MAGE-457

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: evan-masseau

sdk/forms/src/main/java/com/klaviyo/forms/webview/KlaviyoWebViewClient.kt

@@ -11,6 +11,9 @@ import android.webkit.WebResourceResponse
 import android.webkit.WebView
 import android.webkit.WebViewClient as AndroidWebViewClient
 import androidx.core.net.toUri
+import androidx.webkit.WebViewCompat
+import androidx.webkit.WebViewFeature.WEB_MESSAGE_LISTENER
+import androidx.webkit.WebViewFeature.isFeatureSupported
 import com.klaviyo.core.Registry
 import com.klaviyo.core.config.Clock
 import com.klaviyo.core.utils.WeakReferenceDelegate
@@ -141,6 +144,18 @@ internal class KlaviyoWebViewClient() : AndroidWebViewClient(), WebViewClient, J
         webView?.let { webView ->
             Registry.threadHelper.runOnUiThread {
                 Registry.log.verbose("Clear IAF WebView reference")
+                val nativeBridge = Registry.get<NativeBridge>()
+
+                if (isFeatureSupported(WEB_MESSAGE_LISTENER)) {
+                    // Explicitly remove the listener: On some vendors' implementation of webview,
+                    // failure to remove the listener results in a memory leak.
+                    WebViewCompat.removeWebMessageListener(webView, nativeBridge.name)
+                } else {
+                    // For completeness, remove the JS interface if WEB_MESSAGE_LISTENER
+                    // is not supported, although [destroy] should clean this up internally
+                    webView.removeJavascriptInterface(nativeBridge.name)
+                }
+
                 webView.destroy()
                 this.webView = null
             }

sdk/forms/src/test/java/com/klaviyo/forms/webview/KlaviyoWebViewClientTest.kt

@@ -151,6 +151,9 @@ class KlaviyoWebViewClientTest : BaseTest() {
 
         mockkStatic(WebViewCompat::class)
         every { WebViewCompat.addWebMessageListener(any(), any(), any(), any()) } just runs
+        every { WebViewCompat.removeWebMessageListener(any(), any()) } just runs
+
+        every { anyConstructed<KlaviyoWebView>().removeJavascriptInterface(any()) } just runs
     }
 
     @After
@@ -345,6 +348,28 @@ class KlaviyoWebViewClientTest : BaseTest() {
         verifyDestroy()
     }
 
+    @Test
+    fun `destroyWebView removes WebMessageListener when supported`() {
+        val client = KlaviyoWebViewClient()
+        client.initializeWebView()
+        client.destroyWebView()
+
+        verify { WebViewCompat.removeWebMessageListener(any(), eq("MockNativeBridge")) }
+    }
+
+    @Test
+    fun `destroyWebView removes JavascriptInterface when WebMessageListener unsupported`() {
+        every { WebViewFeature.isFeatureSupported(WebViewFeature.WEB_MESSAGE_LISTENER) } returns false
+        every { anyConstructed<KlaviyoWebView>().addJavascriptInterface(any(), any()) } just runs
+
+        val client = KlaviyoWebViewClient()
+        client.initializeWebView()
+        client.destroyWebView()
+
+        verify { anyConstructed<KlaviyoWebView>().removeJavascriptInterface(eq("MockNativeBridge")) }
+        verify(inverse = true) { WebViewCompat.removeWebMessageListener(any(), any()) }
+    }
+
     @Test
     fun `verify detachWebView fails on a null webview`() {
         val client = KlaviyoWebViewClient()