feat(tao): forward back/forward mouse buttons to Compose

decorated-window-tao/api/decorated-window-tao.api

@@ -1261,6 +1261,8 @@ public final class dev/nucleusframework/window/tao/TaoMonitors {
 
 public final class dev/nucleusframework/window/tao/TaoMouseButton {
 	public static final field $stable I
+	public static final field BACK I
+	public static final field FORWARD I
 	public static final field INSTANCE Ldev/nucleusframework/window/tao/TaoMouseButton;
 	public static final field LEFT I
 	public static final field MIDDLE I

decorated-window-tao/src/main/kotlin/dev/nucleusframework/window/tao/TaoEventConstants.kt

@@ -169,5 +169,7 @@ public object TaoMouseButton {
     public const val LEFT: Int = 0
     public const val RIGHT: Int = 1
     public const val MIDDLE: Int = 2
-    public const val OTHER: Int = 3
+    public const val BACK: Int = 3
+    public const val FORWARD: Int = 4
+    public const val OTHER: Int = 5
 }

decorated-window-tao/src/main/kotlin/dev/nucleusframework/window/tao/popup/TaoPopupSceneLayerLinux.kt

@@ -821,6 +821,8 @@ internal class TaoPopupSceneLayerLinux(
         when (code) {
             TaoMouseButton.RIGHT -> PointerButton.Secondary
             TaoMouseButton.MIDDLE -> PointerButton.Tertiary
+            TaoMouseButton.BACK -> PointerButton.Back
+            TaoMouseButton.FORWARD -> PointerButton.Forward
             else -> PointerButton.Primary
         }
 

decorated-window-tao/src/main/kotlin/dev/nucleusframework/window/tao/scene/AbstractTaoComposeSceneHost.kt

@@ -137,6 +137,8 @@ internal abstract class AbstractTaoComposeSceneHost {
             TaoMouseButton.LEFT -> PointerButton.Primary
             TaoMouseButton.RIGHT -> PointerButton.Secondary
             TaoMouseButton.MIDDLE -> PointerButton.Tertiary
+            TaoMouseButton.BACK -> PointerButton.Back
+            TaoMouseButton.FORWARD -> PointerButton.Forward
             else -> PointerButton.Primary
         }
 

decorated-window-tao/src/main/native/linux/nucleus_tao_linux_widget.c

@@ -988,16 +988,18 @@ typedef struct {
     double        delta_y;
 } gdk_event_scroll_t;
 
-/* Map GTK's native button code (1 = LEFT, 2 = MIDDLE, 3 = RIGHT) to
- * Tao's AWT-style encoding (`TaoMouseButton.LEFT = 0`, `RIGHT = 1`,
- * `MIDDLE = 2`). Anything else stays a passthrough — Compose's
- * `mapButton` falls back to `Primary` for unknown codes. */
+/* Map GTK's native button code (1 = LEFT, 2 = MIDDLE, 3 = RIGHT,
+ * 8 = BACK, 9 = FORWARD) to Tao's AWT-style encoding
+ * (`TaoMouseButton.LEFT = 0` … `FORWARD = 4`, `OTHER = 5`) — the same
+ * codes `events.rs` `mouse_button_code` sends for the main surface. */
 static int gtk_button_to_tao(unsigned int gtk_button) {
     switch (gtk_button) {
         case 1: return 0; /* LEFT */
         case 2: return 2; /* MIDDLE */
         case 3: return 1; /* RIGHT */
-        default: return (int) gtk_button;
+        case 8: return 3; /* BACK */
+        case 9: return 4; /* FORWARD */
+        default: return 5; /* OTHER */
     }
 }
 

decorated-window-tao/src/main/native/src/events.rs

@@ -245,7 +245,25 @@ pub(crate) const TOUCH_FORCE_UNKNOWN: jint = -1;
 pub(crate) const MOUSE_BUTTON_LEFT: jint = 0;
 pub(crate) const MOUSE_BUTTON_RIGHT: jint = 1;
 pub(crate) const MOUSE_BUTTON_MIDDLE: jint = 2;
-pub(crate) const MOUSE_BUTTON_OTHER: jint = 3;
+pub(crate) const MOUSE_BUTTON_BACK: jint = 3;
+pub(crate) const MOUSE_BUTTON_FORWARD: jint = 4;
+pub(crate) const MOUSE_BUTTON_OTHER: jint = 5;
+
+// Raw `MouseButton::Other(n)` numbers tao reports for the back / forward side
+// buttons: `XBUTTON1` / `XBUTTON2` on Windows, X11/GDK buttons 8 / 9 on Linux,
+// `NSEvent.buttonNumber` 3 / 4 on macOS.
+#[cfg(target_os = "windows")]
+const OTHER_BACK: u16 = 1;
+#[cfg(target_os = "windows")]
+const OTHER_FORWARD: u16 = 2;
+#[cfg(target_os = "macos")]
+const OTHER_BACK: u16 = 3;
+#[cfg(target_os = "macos")]
+const OTHER_FORWARD: u16 = 4;
+#[cfg(not(any(target_os = "windows", target_os = "macos")))]
+const OTHER_BACK: u16 = 8;
+#[cfg(not(any(target_os = "windows", target_os = "macos")))]
+const OTHER_FORWARD: u16 = 9;
 
 // ── User events posted from JNI calls into the event loop ─────────────────
 
@@ -682,6 +700,8 @@ pub(crate) fn mouse_button_code(b: MouseButton) -> jint {
         MouseButton::Left => MOUSE_BUTTON_LEFT,
         MouseButton::Right => MOUSE_BUTTON_RIGHT,
         MouseButton::Middle => MOUSE_BUTTON_MIDDLE,
+        MouseButton::Other(OTHER_BACK) => MOUSE_BUTTON_BACK,
+        MouseButton::Other(OTHER_FORWARD) => MOUSE_BUTTON_FORWARD,
         _ => MOUSE_BUTTON_OTHER,
     }
 }

decorated-window-tao/src/main/native/vendor/tao/src/platform_impl/macos/view.rs

@@ -1152,14 +1152,24 @@ extern "C" fn right_mouse_up(this: &NSView, _sel: Sel, event: &NSEvent) {
   mouse_click(this, event, MouseButton::Right, ElementState::Released);
 }
 
+// Nucleus: `otherMouseDown:` fires for every button past the right one, so
+// read `buttonNumber` instead of assuming Middle — 3/4 are the back/forward
+// side buttons, surfaced as `Other(3)` / `Other(4)`.
+fn other_mouse_button(event: &NSEvent) -> MouseButton {
+  match event.buttonNumber() {
+    2 => MouseButton::Middle,
+    n => MouseButton::Other(n as u16),
+  }
+}
+
 extern "C" fn other_mouse_down(this: &NSView, _sel: Sel, event: &NSEvent) {
   mouse_motion(this, event);
-  mouse_click(this, event, MouseButton::Middle, ElementState::Pressed);
+  mouse_click(this, event, other_mouse_button(event), ElementState::Pressed);
 }
 
 extern "C" fn other_mouse_up(this: &NSView, _sel: Sel, event: &NSEvent) {
   mouse_motion(this, event);
-  mouse_click(this, event, MouseButton::Middle, ElementState::Released);
+  mouse_click(this, event, other_mouse_button(event), ElementState::Released);
 }
 
 fn mouse_motion(this: &NSView, event: &NSEvent) {

decorated-window-tao/src/test/kotlin/dev/nucleusframework/window/tao/TaoMouseButtonWireDriftTest.kt

@@ -0,0 +1,40 @@
+package dev.nucleusframework.window.tao
+
+import java.io.File
+import java.lang.reflect.Modifier
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.fail
+
+/**
+ * Mouse-button codes are written by hand on both sides of the JNI boundary:
+ * `events.rs` `MOUSE_BUTTON_*` and [TaoMouseButton]. A drift is silent — the
+ * Rust "other" code once shared its number with [TaoMouseButton.BACK], so
+ * every extra button reached Compose as Back — so compare them here.
+ */
+class TaoMouseButtonWireDriftTest {
+    @Test
+    fun `Rust MOUSE_BUTTON codes match TaoMouseButton`() {
+        val rust =
+            RUST_CODE
+                .findAll(eventsRs().readText())
+                .associate { it.groupValues[1] to it.groupValues[2].toInt() }
+        val kotlin =
+            TaoMouseButton::class.java.declaredFields
+                .filter { Modifier.isStatic(it.modifiers) && it.type == Integer.TYPE && it.name != "\$stable" }
+                .associate { it.name to it.getInt(null) }
+        assertEquals(kotlin, rust, "events.rs MOUSE_BUTTON_* vs TaoMouseButton")
+    }
+
+    private fun eventsRs(): File {
+        val relative = "src/main/native/src/events.rs"
+        // Module directory first (Gradle), then the repository root (IDE).
+        val candidates = listOf(File(relative), File("decorated-window-tao", relative))
+        return candidates.firstOrNull { it.isFile }
+            ?: fail("cannot find $relative from ${File("").absolutePath} (tried ${candidates.map { it.path }})")
+    }
+
+    private companion object {
+        val RUST_CODE = Regex("""pub\(crate\) const MOUSE_BUTTON_(\w+): jint = (\d+);""")
+    }
+}