Give the native call component its view of Matrix

The factory lives in libraries/matrix/impl because that is the only module compiled against the Rust SDK, and is app-scoped because a call is started for whichever account it belongs to rather than the one on screen.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

features/callnative/api/build.gradle.kts

@@ -13,8 +13,18 @@ android {
     namespace = "io.element.android.features.callnative.api"
 }
 
+// Temporary: `-PelementCallLocalVersion` points this at a locally published build of
+// element-call-android. Goes with the repositories in settings.gradle.kts.
+val elementCallVersion: String = providers.gradleProperty("elementCallLocalVersion")
+    .getOrElse(libs.versions.element.call.get())
+
 dependencies {
-    // api, not implementation: CallData is part of NativeCallEntryPoint's signature.
+    // api, not implementation: ElementCallMatrixTransport is part of ElementCallTransportFactory's
+    // signature, and CallData of NativeCallEntryPoint's.
+    // api, so that consumers of this module inherit the versions the BOM pins - the artifact
+    // below is declared without one.
+    api(platform("io.element.android:element-call-bom:$elementCallVersion"))
+    api(libs.element.call.api)
     api(projects.features.call.api)
     implementation(projects.libraries.architecture)
     implementation(projects.libraries.matrix.api)

features/callnative/api/src/main/kotlin/io/element/android/features/callnative/api/ElementCallTransportFactory.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2026 Element Creations Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.features.callnative.api
+
+import io.element.android.call.api.matrix.ElementCallMatrixTransport
+import io.element.android.libraries.matrix.api.MatrixClient
+
+/**
+ * Makes the native call's view of Matrix for a session.
+ *
+ * The component's turnkey transport is built over a raw Rust SDK client, and only
+ * `libraries/matrix/impl` is compiled against the SDK. This is the seam that keeps it that way: the
+ * implementation lives there, everything else takes a [MatrixClient] and asks.
+ *
+ * A factory rather than a binding for the transport itself, because the call is started from app scope
+ * - a call can be placed for an account that is not the one on screen - and the session it belongs to
+ * is known only as an id until a client is fetched for it.
+ */
+fun interface ElementCallTransportFactory {
+    fun create(client: MatrixClient): ElementCallMatrixTransport
+}