diff --git a/app/src/main/kotlin/io/flamenet/messenger/app/ChatScreens.kt b/app/src/main/kotlin/io/flamenet/messenger/app/ChatScreens.kt
index 21464bc..27594e3 100644
--- a/app/src/main/kotlin/io/flamenet/messenger/app/ChatScreens.kt
+++ b/app/src/main/kotlin/io/flamenet/messenger/app/ChatScreens.kt
@@ -2565,15 +2565,7 @@ fun RegisteredDevicesSection(
                         }
                     }
                     Text(
-                        device.createdAt?.let { raw ->
-                            runCatching {
-                                val instant = java.time.Instant.parse(raw)
-                                val fmt = java.time.format.DateTimeFormatter
-                                    .ofPattern("MMM d, yyyy HH:mm")
-                                    .withZone(java.time.ZoneId.systemDefault())
-                                "Registered ${'$'}{fmt.format(instant)}"
-                            }.getOrDefault("Registered $raw")
-                        } ?: "Registered date unknown",
+                        registeredLine(device.createdAt),
                         fontSize = 12.sp,
                         color = Palette.SecondaryText,
                     )
@@ -2671,3 +2663,26 @@ private val DISAPPEAR_LABELS = mapOf(
     86_400 to "a day",
     604_800 to "a week",
 )
+
+/**
+ * "Registered <date>" for one device row.
+ *
+ * 🔴 **This shipped rendering its own source code.** The string was written
+ * `"Registered ${'$'}{fmt.format(instant)}"`, and `${'$'}` emits a LITERAL
+ * dollar sign — so the template was never evaluated and the screen showed
+ * `Registered ${fmt.format(instant)}` to the user. Kotlin cannot warn about
+ * it: escaping a dollar is a legitimate thing to want, just never here.
+ *
+ * Lifted out of the Composable so it can be asserted. A string built inline in
+ * a `Text(...)` is a string nothing can test, which is why this survived.
+ */
+internal fun registeredLine(createdAt: String?): String {
+    val raw = createdAt ?: return "Registered date unknown"
+    return runCatching {
+        val instant = java.time.Instant.parse(raw)
+        val fmt = java.time.format.DateTimeFormatter
+            .ofPattern("MMM d, yyyy HH:mm")
+            .withZone(java.time.ZoneId.systemDefault())
+        "Registered ${fmt.format(instant)}"
+    }.getOrDefault("Registered $raw")
+}
diff --git a/app/src/test/kotlin/io/flamenet/messenger/app/RegisteredLineTest.kt b/app/src/test/kotlin/io/flamenet/messenger/app/RegisteredLineTest.kt
new file mode 100644
index 0000000..4c77387
--- /dev/null
+++ b/app/src/test/kotlin/io/flamenet/messenger/app/RegisteredLineTest.kt
@@ -0,0 +1,39 @@
+package io.flamenet.messenger.app
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+/**
+ * The device row's "Registered <date>" line.
+ *
+ * 🔴 **This shipped rendering its own source code.** The string was written
+ * with an escaped dollar, so the template was never evaluated and the screen
+ * showed `Registered ${fmt.format(instant)}` to the user. Nothing could warn
+ * about it — escaping a dollar is legitimate, just never there — and nothing
+ * could test it either, because it was built inline inside a `Text(...)`.
+ */
+class RegisteredLineTest {
+
+    @Test
+    fun `a real timestamp becomes a date, not template source`() {
+        val line = registeredLine("2026-08-29T14:35:00Z")
+        assertFalse("\${" in line, "the template was not evaluated: $line")
+        assertFalse("fmt.format" in line, "source text reached the screen: $line")
+        assertTrue(line.startsWith("Registered "), line)
+        assertTrue("2026" in line, "the year should be in there somewhere: $line")
+    }
+
+    /** An unparseable value is shown as-is rather than swallowed. */
+    @Test
+    fun `an unparseable timestamp falls back to the raw value`() {
+        assertEquals("Registered whenever", registeredLine("whenever"))
+    }
+
+    /** ⚠️ Absent is not the same as unparseable, and must not read as a date. */
+    @Test
+    fun `a missing timestamp says so`() {
+        assertEquals("Registered date unknown", registeredLine(null))
+    }
+}