Play installs the Linux runtime on a fresh install, on the loading screen

Play and Desktop UI are enabled without a runtime. The session's loading screen downloads and
unpacks it first, reporting on its usual step line and bar ("downloading the Linux runtime · 332
of 791 MB", then checking, then unpacking), and starts the session when it is in. A failure ends
on the loading screen with the reason. Non-Adreno devices still get the warning before any
download. Setup > Linux runtime is unchanged.

app/src/main/java/com/steamdeck/launcher/MainActivity.kt

@@ -203,7 +203,12 @@ class MainActivity : ComponentActivity() {
                         theme = theme,
                     ),
                     FrontEndActions(
-                        onPlay = { startActivity(Intent(this, SessionActivity::class.java)) },
+                        onPlay = {
+                            // No runtime and not an Adreno: the same warning Setup gives, before any download.
+                            val warn = installed == null && !com.steamdeck.launcher.core.DeviceSupport.adreno()
+                            if (warn && available != null) showNonAdreno = available
+                            else startActivity(Intent(this, SessionActivity::class.java))
+                        },
                         onPlayDesktopUi = {
                             startActivity(Intent(this, SessionActivity::class.java)
                                 .putExtra(SessionService.EXTRA_STEAM_UI, "desktop"))

app/src/main/java/com/steamdeck/launcher/SessionActivity.kt

@@ -140,6 +140,7 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
         surfaceView.pointerIcon = noCursor
 
         loading = LoadingState(this)
+        if (!SessionState.running && com.steamdeck.launcher.runtime.LinuxRuntimeInstaller.installedVersion(this) == null) installRuntimeThenStart()
         hud = PerfHud(this)
         hud.onPresentingWindowChanged = {
             if (FrameGen.engine(this) != FrameGen.ENGINE_OFF) CompositorHost.rearmFrameGen { applyFrameGen() }
@@ -254,7 +255,47 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
 
     // ── Compositor ──────────────────────────────────────────────────────────────────────────
 
+    /** True while the loading screen is installing the Linux runtime; the session waits for it. */
+    @Volatile private var installingRuntime = false
+
+    /**
+     * First Play on a fresh install: the runtime is downloaded and unpacked here, on the loading
+     * screen's own line and bar, and the session starts when it is in. Nothing else changes.
+     */
+    private fun installRuntimeThenStart() {
+        installingRuntime = true
+        loading.step = "downloading the Linux runtime"
+        loading.percent = -1
+        Thread({
+            val release = com.steamdeck.launcher.runtime.LinuxRuntimeInstaller.fetchRelease()
+            val mb = release?.let { it.size / 1_000_000 } ?: 0L
+            val ok = release != null && com.steamdeck.launcher.runtime.LinuxRuntimeInstaller.install(this, release) { stage, p ->
+                uiHandler.post {
+                    loading.percent = p
+                    loading.step = when (stage) {
+                        "Downloading" -> if (p >= 0 && mb > 0) "downloading the Linux runtime · ${p * mb / 100} of $mb MB" else "downloading the Linux runtime"
+                        "Verifying" -> "checking the Linux runtime"
+                        else -> "unpacking the Linux runtime"
+                    }
+                }
+            }
+            uiHandler.post {
+                installingRuntime = false
+                if (!ok) {
+                    loading.showEnded(if (release == null) "Could not reach the runtime catalog. Check the connection and press Play again."
+                        else "The Linux runtime did not install. Check the connection and press Play again.")
+                    return@post
+                }
+                loading.percent = -1
+                loading.step = "Starting the session…"
+                // The surface may have come and gone while the download ran; start on the live one.
+                if (surfaceView.holder.surface?.isValid == true) surfaceCreated(surfaceView.holder)
+            }
+        }, "runtime-install").start()
+    }
+
     override fun surfaceCreated(holder: SurfaceHolder) {
+        if (installingRuntime) return
         val runtimeDir = File(filesDir, ".wayland-rt").apply { mkdirs() }
         // The compositor hands this keymap to wl_keyboard clients, which is how the guest reads
         // the evdev codes we inject.
@@ -423,7 +464,7 @@ class SessionActivity : ComponentActivity(), SurfaceHolder.Callback {
             override fun run() {
                 if (!watching) return
                 if (loading.visible && !loading.ended) {
-                    loading.update(this@SessionActivity, SessionState.logFile)
+                    if (!installingRuntime) loading.update(this@SessionActivity, SessionState.logFile)
                     if (ticks++ % 2 == 0) loading.tick()
                 }
                 handler.postDelayed(this, 500)

app/src/main/java/com/steamdeck/launcher/ui/FrontEndScreen.kt

@@ -551,8 +551,9 @@ private fun Content(s: FrontEndState, selected: String, a: FrontEndActions, modi
                 Rise(0) { Eyebrow("Steam") }
                 Rise(3) {
                     Actions {
-                        PrimaryButton("Play", enabled = s.ready && !s.busy, onClick = a.onPlay)
-                        SecondaryButton("Desktop UI", enabled = s.ready && !s.busy, onClick = a.onPlayDesktopUi)
+                        // Enabled without a runtime: the session's loading screen installs it first.
+                        PrimaryButton("Play", enabled = !s.busy, onClick = a.onPlay)
+                        SecondaryButton("Desktop UI", enabled = !s.busy, onClick = a.onPlayDesktopUi)
                         Cog(a.onSteamSettings)
                     }
                 }