diff --git a/app/src/test/java/de/jeanlucmakiola/clockula/ArchitectureRulesTest.kt b/app/src/test/java/de/jeanlucmakiola/clockula/ArchitectureRulesTest.kt
index 69309d3..ae62d7b 100644
--- a/app/src/test/java/de/jeanlucmakiola/clockula/ArchitectureRulesTest.kt
+++ b/app/src/test/java/de/jeanlucmakiola/clockula/ArchitectureRulesTest.kt
@@ -70,6 +70,53 @@ class ArchitectureRulesTest {
         assertThat(offenders).isEmpty()
     }
 
+    /**
+     * Compose may live in `ui/` and in the one activity that hosts it, and
+     * nowhere else — the shell's decision surface is pure Kotlin by
+     * construction, which is what earns the no-Robolectric posture (D17).
+     */
+    private val composeAllowlist: List<String> = kotlinSources
+        .filter { file -> file.readLines().any { it.startsWith("import androidx.compose.") } }
+        .map { it.invariantSeparatorsPath }
+
+    @Test
+    fun `Compose stays inside the ui package and its one host activity`() {
+        val offenders = composeAllowlist.filterNot {
+            it.contains("de/jeanlucmakiola/clockula/ui/") ||
+                it.endsWith("de/jeanlucmakiola/clockula/MainActivity.kt")
+        }
+
+        assertThat(offenders).isEmpty()
+    }
+
+    @Test
+    fun `the ui layer names no literal colour`() {
+        val literals = listOf(
+            "Color(0x",
+            "Color.Red", "Color.Green", "Color.Blue", "Color.Yellow", "Color.Cyan",
+            "Color.Magenta", "Color.White", "Color.Black", "Color.Gray",
+            "Color.LightGray", "Color.DarkGray",
+        )
+        val ui = kotlinSources.filter { file ->
+            val path = file.invariantSeparatorsPath
+            path.contains("de/jeanlucmakiola/clockula/ui/") &&
+                !path.contains("de/jeanlucmakiola/clockula/ui/theme/")
+        }
+
+        val offenders = ui.containing(*literals.toTypedArray())
+
+        assertThat(offenders).isEmpty()
+    }
+
+    @Test
+    fun `exactly one file outside the ui package may import Compose`() {
+        val outsideUi = composeAllowlist.filterNot {
+            it.contains("de/jeanlucmakiola/clockula/ui/")
+        }
+
+        assertThat(outsideUi).hasSize(1)
+    }
+
     @Test
     fun `the alarm engine and its pure neighbours stay free of Android types`() {
         val jvmTestable = kotlinSources.filter { file ->