2 files changed, 21 insertions, 5 deletions
diff --git a/src/macos/Sources/PardesView.swift b/src/macos/Sources/PardesView.swift
index 5c5bc8ba..bfc8a060 100644
--- a/src/macos/Sources/PardesView.swift
+++ b/src/macos/Sources/PardesView.swift
@@ -1730,11 +1730,25 @@ final class PardesView: NSView {
     override func rightMouseDown(with event: NSEvent) { beginClick(PARDES_MOUSE_RIGHT, event) }
     override func rightMouseDragged(with event: NSEvent) { continueClick(event) }
     override func rightMouseUp(with event: NSEvent) { endClick(event) }
-    // otherMouse covers button 2 and up. acme's vocabulary stops at three, so
-    // every one of them lands on middle rather than being invented into a fourth.
-    override func otherMouseDown(with event: NSEvent) { beginClick(PARDES_MOUSE_MIDDLE, event) }
-    override func otherMouseDragged(with event: NSEvent) { continueClick(event) }
-    override func otherMouseUp(with event: NSEvent) { endClick(event) }
+    // Thumb navigation has its own stream so it cannot replace a held
+    // selection button or inherit a resting trackpad's finger count.
+    override func otherMouseDown(with event: NSEvent) {
+        if event.buttonNumber == 2 { beginClick(PARDES_MOUSE_MIDDLE, event); return }
+        guard event.buttonNumber == 3 || event.buttonNumber == 4,
+              let at = cell(for: event) else { return }
+        press(event.buttonNumber == 3 ? PARDES_MOUSE_BACK : PARDES_MOUSE_FORWARD,
+              at: at, mods: pointerModifiers)
+    }
+    override func otherMouseDragged(with event: NSEvent) {
+        if event.buttonNumber == 2 { continueClick(event) }
+    }
+    override func otherMouseUp(with event: NSEvent) {
+        if event.buttonNumber == 2 { endClick(event); return }
+        guard event.buttonNumber == 3 || event.buttonNumber == 4,
+              let at = cell(for: event) else { return }
+        release(event.buttonNumber == 3 ? PARDES_MOUSE_BACK : PARDES_MOUSE_FORWARD,
+                at: at, mods: pointerModifiers)
+    }
 
     /// A deep press, which is a second gesture layered on the click already in
     /// flight. AppKit keeps sending stage-2 events while the finger stays down,
diff --git a/src/macos/pardes.h b/src/macos/pardes.h
index 845c8096..546273d9 100644
--- a/src/macos/pardes.h
+++ b/src/macos/pardes.h
@@ -167,6 +167,8 @@ typedef enum {
   PARDES_MOUSE_WHEEL_LEFT = 5,
   PARDES_MOUSE_WHEEL_RIGHT = 6,
   PARDES_MOUSE_NONE = 7,
+  PARDES_MOUSE_BACK = 8,
+  PARDES_MOUSE_FORWARD = 9,
 } pardes_mouse_button_e;
 
 typedef enum {