Remove haskellUseScrollDemo FFI and runtime app-switching mechanism

The useScrollDemo JNI method + haskellUseScrollDemo FFI export were test
infrastructure that leaked into the core library bridge, forcing every app
that replaces App.hs to either export the symbol or work around the linker
error.

Fix: build the scroll-demo test APK/simulator-app with test/ScrollDemoMain.hs
as the entry point so the app starts directly in scroll-demo mode. No
runtime switching is needed, so the whole mechanism can be deleted:

- cbits/jni_bridge.c: remove useScrollDemo JNI method
- src/HaskellMobile/App.hs: remove haskellUseScrollDemo foreign export
- android/java/.../MainActivity.java: remove native useScrollDemo() and
  the test_mode intent check
- include/HaskellMobile.h: remove haskellUseScrollDemo declaration
- ios/HaskellMobile/HaskellBridge.swift: remove useScrollDemo() wrapper
- ios/HaskellMobile/ContentView.swift: remove --scroll-demo flag handling
- nix/emulator-scroll.nix: build scroll APK with ScrollDemoMain.hs
- nix/simulator-scroll.nix: build scroll simulator app with ScrollDemoMain.hs
- test/ScrollDemoMain.hs: new entry point using scrollDemoApp directly

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: jappeace-sloth

android/java/me/jappie/haskellmobile/MainActivity.java

@@ -14,7 +14,6 @@ public class MainActivity extends Activity implements View.OnClickListener {
     }
 
     private native String greet(String name);
-    private native void useScrollDemo();
     private native void renderUI();
     private native void onButtonClick(View view);
     private native void onTextChange(View view, String text);
@@ -30,10 +29,6 @@ public class MainActivity extends Activity implements View.OnClickListener {
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         onLifecycleCreate();
-        String testMode = getIntent().getStringExtra("test_mode");
-        if ("scroll_demo".equals(testMode)) {
-            useScrollDemo();
-        }
         // Render UI from Haskell instead of XML layout
         renderUI();
     }

cbits/jni_bridge.c

@@ -24,7 +24,6 @@ extern void haskellOnLifecycle(void *ctx, int eventType);
 extern void haskellRenderUI(void *ctx);
 extern void haskellOnUIEvent(void *ctx, int callbackId);
 extern void haskellOnUITextChange(void *ctx, int callbackId, const char *text);
-extern void haskellUseScrollDemo(void);
 
 /* Android UI bridge (from ui_bridge_android.c) */
 extern void setup_android_ui_bridge(JNIEnv *env, jobject activity, void *haskellCtx);
@@ -77,13 +76,6 @@ JNI_METHOD(greet)(JNIEnv *env, jobject thiz, jstring jname)
 
 /* --- UI bridge JNI methods --- */
 
-JNIEXPORT void JNICALL
-JNI_METHOD(useScrollDemo)(JNIEnv *env, jobject obj)
-{
-    (void)env; (void)obj;
-    haskellUseScrollDemo();
-}
-
 JNIEXPORT void JNICALL
 JNI_METHOD(renderUI)(JNIEnv *env, jobject thiz)
 {

include/HaskellMobile.h

@@ -46,8 +46,5 @@ void haskellRenderUI(void *ctx);
  * ctx must be a pointer returned by haskellCreateContext(). */
 void haskellOnUIEvent(void *ctx, int32_t callbackId);
 
-/* Switch the running app to the scroll demo.
- * Called by test harnesses to exercise the ScrollView widget end-to-end. */
-void haskellUseScrollDemo(void);
 
 #endif /* HASKELL_MOBILE_H */

ios/HaskellMobile/ContentView.swift

@@ -10,10 +10,6 @@ struct HaskellUIView: UIViewControllerRepresentable {
         let ptr = Unmanaged.passUnretained(vc).toOpaque()
         setup_ios_ui_bridge(ptr, HaskellBridge.getContext())
 
-        if CommandLine.arguments.contains("--scroll-demo") {
-            HaskellBridge.useScrollDemo()
-        }
-
         HaskellBridge.renderUI()
 
         // CI auto-test: simulate button tap 3s after the initial render.

ios/HaskellMobile/HaskellBridge.swift

@@ -50,9 +50,4 @@ class HaskellBridge {
         return context
     }
 
-    /// Switch the running app to the scroll demo.
-    /// Call before renderUI() to exercise ScrollView end-to-end in integration tests.
-    static func useScrollDemo() {
-        haskellUseScrollDemo()
-    }
 }

nix/emulator-scroll.nix

@@ -1,6 +1,7 @@
 # Android emulator ScrollView integration test.
 #
-# Boots an emulator, installs the APK in scroll-demo mode, and verifies:
+# Builds the APK with ScrollDemoMain.hs as the entry point so the app starts
+# directly in scroll-demo mode — no runtime switching needed.  Verifies:
 #   1. Haskell emitted a ScrollView node (logcat: createNode type=5)
 #   2. Native view hierarchy contains android.widget.ScrollView (uiautomator)
 #   3. Swiping up reveals the "Reached Bottom" button (uiautomator after swipe)
@@ -18,7 +19,14 @@ let
     config.android_sdk.accept_license = true;
   };
 
-  apk = import ./apk.nix { inherit sources; };
+  lib = import ./lib.nix { inherit sources; };
+  scrollAndroid = import ./android.nix { inherit sources; mainModule = ../test/ScrollDemoMain.hs; };
+  apk = lib.mkApk {
+    sharedLib = scrollAndroid;
+    androidSrc = ../android;
+    apkName = "haskell-mobile-scroll.apk";
+    name = "haskell-mobile-scroll-apk";
+  };
 
   androidComposition = pkgs.androidenv.composeAndroidPackages {
     platformVersions = [ "34" ];
@@ -230,9 +238,9 @@ echo "APK installed."
 echo "=== Preparing logcat ==="
 "$ADB" -s "emulator-$PORT" logcat -c
 
-# --- Launch activity with scroll_demo intent extra ---
-echo "=== Launching $PACKAGE/$ACTIVITY in scroll-demo mode ==="
-"$ADB" -s "emulator-$PORT" shell am start -n "$PACKAGE/$ACTIVITY" --es test_mode scroll_demo
+# --- Launch activity ---
+echo "=== Launching $PACKAGE/$ACTIVITY ==="
+"$ADB" -s "emulator-$PORT" shell am start -n "$PACKAGE/$ACTIVITY"
 
 # --- Wait for initial render ---
 echo "=== Waiting for initial render (timeout: 120s) ==="

nix/simulator-scroll.nix

@@ -1,10 +1,10 @@
 # iOS Simulator ScrollView integration test.
 #
-# Builds and installs the app with --scroll-demo --autotest, then verifies:
+# Builds the app with ScrollDemoMain.hs as the entry point so the app starts
+# directly in scroll-demo mode, then verifies:
 #   1. Haskell emitted a ScrollView node (os_log: createNode(type=5))
 #   2. The "Reached Bottom" button callback fired (os_log: Click dispatched: callbackId=0)
 #
-# The --scroll-demo flag switches the app to scrollDemoApp before the first render.
 # The --autotest flag fires event 0 (the "Reached Bottom" button) 3s after render.
 #
 # Independent from other simulator tests — can run in parallel.
@@ -16,7 +16,13 @@
 let
   pkgs = import sources.nixpkgs {};
 
-  simulatorApp = import ./simulator-app.nix { inherit sources; };
+  scrollIos = import ./ios.nix { inherit sources; mainModule = ../test/ScrollDemoMain.hs; simulator = true; };
+  simulatorApp = lib.mkSimulatorApp {
+    iosLib = scrollIos;
+    iosSrc = ../ios;
+    name = "haskell-mobile-scroll-simulator-app";
+  };
+  lib = import ./lib.nix { inherit sources; };
 
   xcodegen = pkgs.xcodegen;
 
@@ -174,9 +180,9 @@ LOG_PID=$!
 # Give log stream time to fully attach before launching
 sleep 5
 
-# --- Launch app with --scroll-demo --autotest ---
-echo "=== Launching $BUNDLE_ID with --scroll-demo --autotest ==="
-xcrun simctl launch "$SIM_UDID" "$BUNDLE_ID" --scroll-demo --autotest
+# --- Launch app with --autotest ---
+echo "=== Launching $BUNDLE_ID with --autotest ==="
+xcrun simctl launch "$SIM_UDID" "$BUNDLE_ID" --autotest
 
 # --- Wait for initial render ---
 echo "=== Waiting for initial render (timeout: 60s) ==="
@@ -200,7 +206,7 @@ if [ $RENDER_DONE -eq 0 ]; then
     xcrun simctl terminate "$SIM_UDID" "$BUNDLE_ID" 2>/dev/null || true
     sleep 3
     > "$LOG_FILE"
-    xcrun simctl launch "$SIM_UDID" "$BUNDLE_ID" --scroll-demo --autotest
+    xcrun simctl launch "$SIM_UDID" "$BUNDLE_ID" --autotest
 
     POLL_TIMEOUT=60
     POLL_ELAPSED=0

src/HaskellMobile/App.hs

@@ -1,13 +1,12 @@
-{-# LANGUAGE ForeignFunctionInterface #-}
 {-# LANGUAGE OverloadedStrings #-}
 -- | Default implementation of the mobile app.
 -- Provides 'loggingMobileContext' as the application context and a simple
 -- counter demo as the default UI.
-module HaskellMobile.App (mobileApp, scrollDemoApp, haskellUseScrollDemo) where
+module HaskellMobile.App (mobileApp, scrollDemoApp) where
 
 import Data.IORef (IORef, newIORef, readIORef, modifyIORef')
 import Data.Text (pack)
-import HaskellMobile.Types (MobileApp(..), runMobileApp)
+import HaskellMobile.Types (MobileApp(..))
 import HaskellMobile.Lifecycle (loggingMobileContext)
 import HaskellMobile.Widget (Widget(..))
 import System.IO.Unsafe (unsafePerformIO)
@@ -53,9 +52,3 @@ scrollDemoView = pure $ ScrollView
     )
   ]
 
--- | Switch the running app to the scroll demo. Called via JNI (Android) or
--- direct FFI (iOS) when the test harness requests scroll-demo mode.
-haskellUseScrollDemo :: IO ()
-haskellUseScrollDemo = runMobileApp scrollDemoApp
-
-foreign export ccall haskellUseScrollDemo :: IO ()

test/ScrollDemoMain.hs

@@ -0,0 +1,14 @@
+{-# LANGUAGE OverloadedStrings #-}
+-- | Mobile entry point for the scroll-demo test app.
+--
+-- Used by the emulator and simulator ScrollView integration tests.
+-- Starts directly in scroll-demo mode so no runtime switching is needed.
+module Main where
+
+import HaskellMobile (runMobileApp, platformLog)
+import HaskellMobile.App (scrollDemoApp)
+
+main :: IO ()
+main = do
+  runMobileApp scrollDemoApp
+  platformLog "Scroll demo app registered"