diff --git a/docs/build-status.md b/docs/build-status.md
index 4e7f60c..7b4106a 100644
--- a/docs/build-status.md
+++ b/docs/build-status.md
@@ -507,3 +507,16 @@ an elvis-operator bug that printed "no UPnP response" even when UPnP data was pr
 - **Insets/cutout**: Android 15 draws edge-to-edge by default, so the title was running under the
   status-bar clock and the camera cutout. The root column now uses `safeDrawingPadding()`, which
   covers status bar, navigation bar and display cutout.
+
+### Shell-tier readiness shown before a run (2026-08-01)
+`ShizukuAvailability` distinguishes four states and the UI only speaks when it is actionable:
+- **NOT_INSTALLED → says nothing.** Users who don't use Shizuku are never nagged.
+- **INSTALLED_NOT_RUNNING → amber banner** "Shizuku is installed but not running — start it to
+  include shell-tier tests". This is the case worth reminding about: the user has it, but a
+  stopped service silently costs them the whole shell tier.
+- NEEDS_PERMISSION → "running but not authorised, it will ask on first use".
+- READY → green "shell-tier tests will run".
+Detection is listener-based (`addBinderReceivedListenerSticky` + binder-dead), because
+`pingBinder()` is only truthful once ShizukuProvider has delivered the binder — a one-shot poll at
+launch would show a false "not running". Installed-vs-not needs the `<queries>` package-visibility
+entry on Android 11+. Verified on-device: with shizuku_server stopped the banner appears correctly.
diff --git a/echolot-app/app/src/main/kotlin/app/echo_lot/app/MainActivity.kt b/echolot-app/app/src/main/kotlin/app/echo_lot/app/MainActivity.kt
index bf43ffa..1c42332 100644
--- a/echolot-app/app/src/main/kotlin/app/echo_lot/app/MainActivity.kt
+++ b/echolot-app/app/src/main/kotlin/app/echo_lot/app/MainActivity.kt
@@ -115,6 +115,22 @@ private fun EcholotScreen(
         Text("Echolot", fontSize = 26.sp, fontWeight = FontWeight.SemiBold)
         Text("measure, don't guess", color = MaterialTheme.colorScheme.onSurfaceVariant, fontSize = 13.sp)
 
+        // Shell-tier readiness, before the run. Nothing is shown when Shizuku isn't installed —
+        // only users who actually use it get reminded that it must be running.
+        state.shizukuNotice?.let { notice ->
+            Card(
+                Modifier.fillMaxWidth(),
+                colors = CardDefaults.cardColors(
+                    containerColor = if (state.shizukuReady) Color(0xFF14301F) else Color(0xFF3A2E12),
+                ),
+            ) {
+                Text(
+                    notice, Modifier.padding(10.dp), fontSize = 12.sp,
+                    color = if (state.shizukuReady) Color(0xFF9CCFA8) else Color(0xFFFFD08A),
+                )
+            }
+        }
+
         Row(horizontalArrangement = Arrangement.spacedBy(12.dp), verticalAlignment = Alignment.CenterVertically) {
             Button(onClick = onRun, enabled = !state.running) {
                 Text(if (state.running) "Running…" else "Run measurement")
diff --git a/echolot-app/app/src/main/kotlin/app/echo_lot/app/RunViewModel.kt b/echolot-app/app/src/main/kotlin/app/echo_lot/app/RunViewModel.kt
index 3daf3ac..f9042e2 100644
--- a/echolot-app/app/src/main/kotlin/app/echo_lot/app/RunViewModel.kt
+++ b/echolot-app/app/src/main/kotlin/app/echo_lot/app/RunViewModel.kt
@@ -20,6 +20,7 @@ import app.echo_lot.probe.NetworkInventory
 import app.echo_lot.probe.Probe
 import app.echo_lot.probe.ProbeIds
 import app.echo_lot.probe.RouterIdentityProbe
+import app.echo_lot.shizuku.ShizukuAvailability
 import app.echo_lot.shizuku.ShizukuProbe
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
@@ -37,6 +38,9 @@ data class UiState(
     val stepsDone: Int = 0,
     val stepsTotal: Int = 0,
     val etaSeconds: Int = 0,
+    /** Shell-tier readiness, shown before a run; null message = say nothing (Shizuku not installed). */
+    val shizukuNotice: String? = null,
+    val shizukuReady: Boolean = false,
 )
 
 /**
@@ -51,6 +55,24 @@ class RunViewModel(app: Application) : AndroidViewModel(app) {
         private set
 
     private var runJob: kotlinx.coroutines.Job? = null
+    private val stopShizukuObserver: () -> Unit
+
+    init {
+        // Report shell-tier readiness up front. The binder arrives asynchronously, so this is a
+        // listener, not a one-shot poll — otherwise a running Shizuku would look "not running"
+        // for the first moment after launch.
+        stopShizukuObserver = ShizukuAvailability.observe(app) { st ->
+            state = state.copy(
+                shizukuNotice = ShizukuAvailability.describe(st),
+                shizukuReady = st == ShizukuAvailability.State.READY,
+            )
+        }
+    }
+
+    override fun onCleared() {
+        stopShizukuObserver()
+        super.onCleared()
+    }
     // Results collected so far. A cancelled run must still be able to show what it measured.
     private val collected = mutableListOf<Test>()
     private var runIds: RunIds = RunIds()
diff --git a/echolot-app/core-shizuku/src/main/AndroidManifest.xml b/echolot-app/core-shizuku/src/main/AndroidManifest.xml
index 21a1d02..4db7c1f 100644
--- a/echolot-app/core-shizuku/src/main/AndroidManifest.xml
+++ b/echolot-app/core-shizuku/src/main/AndroidManifest.xml
@@ -5,6 +5,12 @@
 
     <uses-permission android:name="moe.shizuku.manager.permission.API_V23" />
 
+    <!-- Android 11+ package visibility: needed to tell "Shizuku installed but stopped"
+         (worth a reminder) apart from "not installed" (say nothing). -->
+    <queries>
+        <package android:name="moe.shizuku.privileged.api" />
+    </queries>
+
     <application>
         <!-- Shizuku binder provider (merged into the host app). -->
         <provider
diff --git a/echolot-app/core-shizuku/src/main/kotlin/app/echo_lot/shizuku/ShizukuAvailability.kt b/echolot-app/core-shizuku/src/main/kotlin/app/echo_lot/shizuku/ShizukuAvailability.kt
new file mode 100644
index 0000000..491a1d8
--- /dev/null
+++ b/echolot-app/core-shizuku/src/main/kotlin/app/echo_lot/shizuku/ShizukuAvailability.kt
@@ -0,0 +1,78 @@
+// SPDX-FileCopyrightText: 2026 Echolot contributors
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package app.echo_lot.shizuku
+
+import android.content.Context
+import android.content.pm.PackageManager
+import rikka.shizuku.Shizuku
+
+/**
+ * Tells the UI whether the shell tier is usable **before** a run starts, so the app can say
+ * "Shizuku isn't running, shell-tier tests will be skipped" instead of silently producing an
+ * UNSUPPORTED result minutes later.
+ *
+ * Detection is reliable but *asynchronous*: `Shizuku.pingBinder()` answers truthfully only once
+ * ShizukuProvider has delivered the binder to this process, which happens shortly after start.
+ * [observe] therefore reports the current state immediately and again whenever the binder
+ * arrives or dies — a poll at t=0 alone would show a false "not running".
+ */
+object ShizukuAvailability {
+
+    const val SHIZUKU_PACKAGE = "moe.shizuku.privileged.api"
+
+    enum class State {
+        /** Running and this app may use it — shell tier will execute. */
+        READY,
+        /** Running, but the user hasn't granted this app permission yet (we can ask). */
+        NEEDS_PERMISSION,
+        /** Shizuku IS installed but its service isn't started — worth reminding this user. */
+        INSTALLED_NOT_RUNNING,
+        /** Shizuku isn't installed at all — say nothing; this user doesn't use the shell tier. */
+        NOT_INSTALLED,
+    }
+
+    /** Is the Shizuku manager installed? Needs the <queries> entry on Android 11+. */
+    fun isInstalled(context: Context): Boolean = runCatching {
+        context.packageManager.getPackageInfo(SHIZUKU_PACKAGE, 0); true
+    }.getOrDefault(false)
+
+    fun current(context: Context): State = when {
+        runCatching { Shizuku.pingBinder() }.getOrDefault(false) ->
+            if (runCatching { Shizuku.checkSelfPermission() == PackageManager.PERMISSION_GRANTED }
+                    .getOrDefault(false)
+            ) State.READY else State.NEEDS_PERMISSION
+        isInstalled(context) -> State.INSTALLED_NOT_RUNNING
+        else -> State.NOT_INSTALLED
+    }
+
+    /**
+     * UI one-liner, or null when nothing should be said. Users without Shizuku get no nag; users
+     * who have it installed but stopped get the reminder that makes the difference between a
+     * full run and a silently skipped shell tier.
+     */
+    fun describe(s: State): String? = when (s) {
+        State.READY -> "Shizuku ready — shell-tier tests will run"
+        State.NEEDS_PERMISSION -> "Shizuku is running but not authorised — it will ask on first use"
+        State.INSTALLED_NOT_RUNNING -> "Shizuku is installed but not running — start it to include shell-tier tests"
+        State.NOT_INSTALLED -> null
+    }
+
+    /**
+     * Reports the state now and on every binder transition. Returns a function that removes the
+     * listeners again (call it from onCleared).
+     */
+    fun observe(context: Context, onChange: (State) -> Unit): () -> Unit {
+        val app = context.applicationContext
+        val received = Shizuku.OnBinderReceivedListener { onChange(current(app)) }
+        val dead = Shizuku.OnBinderDeadListener { onChange(current(app)) }
+        // "Sticky" fires immediately if the binder already arrived before we registered.
+        runCatching { Shizuku.addBinderReceivedListenerSticky(received) }
+        runCatching { Shizuku.addBinderDeadListener(dead) }
+        onChange(current(app))
+        return {
+            runCatching { Shizuku.removeBinderReceivedListener(received) }
+            runCatching { Shizuku.removeBinderDeadListener(dead) }
+        }
+    }
+}