diff --git a/build.gradle.kts b/build.gradle.kts
index ecf7a23..df1330b 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -1,6 +1,31 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
+
+// The Android Gradle Plugin drags its own tooling onto this build script's classpath: gRPC and
+// Netty (io.grpc:grpc-netty), Bouncy Castle (com.android.tools:sdk-common), commons-compress
+// (:repository), jose4j (bundletool) and JDOM (jetifier). The resolutionStrategy in
+// android/build.gradle.kts cannot reach any of it - that block configures the :android project's
+// own configurations, which are resolved separately, so Netty was still landing at 4.1.93.Final
+// there while the floor read 4.1.138.Final.
+//
+// Platforms and constraints only ever raise a version, so a newer one shipped by a future AGP
+// still wins. AGP 9 drops gRPC outright, which retires the Netty half of this entirely.
+buildscript {
+    dependencies {
+        classpath(platform("io.netty:netty-bom:${libs.versions.netty.get()}"))
+        classpath(platform("com.google.protobuf:protobuf-bom:${libs.versions.protobuf.get()}"))
+        constraints {
+            add("classpath", "org.bouncycastle:bcprov-jdk18on:${libs.versions.bouncycastle.get()}")
+            add("classpath", "org.bouncycastle:bcpkix-jdk18on:${libs.versions.bouncycastle.get()}")
+            add("classpath", "org.bouncycastle:bcutil-jdk18on:${libs.versions.bouncycastle.get()}")
+            add("classpath", "org.bitbucket.b_c:jose4j:${libs.versions.jose4j.get()}")
+            add("classpath", "org.jdom:jdom2:${libs.versions.jdom2.get()}")
+            add("classpath", "org.apache.commons:commons-compress:${libs.versions.commonsCompress.get()}")
+        }
+    }
+}
+
 plugins {
     alias(libs.plugins.android.application) apply false
     alias(libs.plugins.kotlin.android) apply false
     alias(libs.plugins.android.library) apply false
-}
\ No newline at end of file
+}
diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index e9c922a..44c0668 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -24,10 +24,17 @@ databindingCommon = "8.9.2"
 
 dokka = "2.2.0"
 
-# Security floors for vulnerable transitive dependencies of the build toolchain: the Android
-# Gradle Plugin's Unified Test Platform (netty, protobuf) and Dokka's engine (jackson, jsoup).
-# These never reach the published AAR - see the resolutionStrategy blocks in
-# android/build.gradle.kts.
+# Security floors for vulnerable transitive dependencies of the build toolchain. None of these
+# reaches the published AAR - releaseRuntimeClasspath carries none of them.
+#
+# They are applied in two places, because the toolchain pulls them onto two classpaths that are
+# resolved independently:
+#
+#   - build.gradle.kts (root buildscript) - AGP's own plugin classpath. gRPC/Netty, Bouncy
+#     Castle, commons-compress, jose4j and JDOM live here. This is the classpath Dependabot
+#     reports against, attributed to settings.gradle.kts.
+#   - android/build.gradle.kts (resolutionStrategy) - the :android project's configurations,
+#     including AGP's Unified Test Platform, plus Dokka's engine (jackson, jsoup).
 #
 # Dependabot does not track these: its Gradle parser only reaches [versions] through a
 # `version.ref` in [libraries]/[plugins], and nothing references them. Re-check them by
@@ -37,6 +44,10 @@ netty = "4.1.138.Final"
 protobuf = "3.25.9"
 jackson = "2.22.2"
 jsoup = "1.23.2"
+bouncycastle = "1.85"
+jose4j = "0.9.6"
+jdom2 = "2.0.6.1"
+commonsCompress = "1.27.1"
 
 [libraries]
 androidx-core-ktx = { group = "androidx.core", name = "core-ktx", version.ref = "coreKtx" }