fix: pass the wheel to programs that report the mouse

src/frontend/terminal/Terminal.tsx

@@ -3095,7 +3095,12 @@ const TerminalInner = forwardRef<TerminalHandle, SSHTerminalProps>(
           }
           return false;
         }
-        if (wheelHasNothingToScroll(terminal.buffer.active)) {
+        if (
+          wheelHasNothingToScroll(
+            terminal.buffer.active,
+            terminal.modes.mouseTrackingMode,
+          )
+        ) {
           ev.preventDefault();
           return false;
         }

src/frontend/terminal/terminal-wheel.ts

@@ -25,9 +25,18 @@ type WheelBuffer = { type: "normal" | "alternate"; baseY: number };
  * A plain wheel on a normal buffer with nothing scrolled off yet. xterm turns
  * that into an arrow key, which walks shell history, so it is dropped. The
  * alternate screen keeps the arrow keys: that is how less and vim scroll.
+ * When the app has mouse reporting on, xterm sends the wheel to the app
+ * instead (tmux attached on the normal screen does this), so it is kept.
  */
-export function wheelHasNothingToScroll(buffer: WheelBuffer): boolean {
-  return buffer.type === "normal" && buffer.baseY === 0;
+export function wheelHasNothingToScroll(
+  buffer: WheelBuffer,
+  mouseTrackingMode: string,
+): boolean {
+  return (
+    mouseTrackingMode === "none" &&
+    buffer.type === "normal" &&
+    buffer.baseY === 0
+  );
 }
 
 /** Pixels per scrolled line, the same step xterm uses for one wheel line. */

tests/frontend/terminal/terminal-wheel.test.ts

@@ -42,14 +42,26 @@ describe("terminalWheelAction", () => {
 
 describe("wheelHasNothingToScroll", () => {
   it("drops the wheel on a normal buffer with no scrollback yet", () => {
-    expect(wheelHasNothingToScroll({ type: "normal", baseY: 0 })).toBe(true);
-    expect(wheelHasNothingToScroll({ type: "normal", baseY: 12 })).toBe(false);
+    expect(wheelHasNothingToScroll({ type: "normal", baseY: 0 }, "none")).toBe(
+      true,
+    );
+    expect(wheelHasNothingToScroll({ type: "normal", baseY: 12 }, "none")).toBe(
+      false,
+    );
   });
 
   it("leaves the alternate screen alone so less and vim still scroll", () => {
-    expect(wheelHasNothingToScroll({ type: "alternate", baseY: 0 })).toBe(
-      false,
-    );
+    expect(
+      wheelHasNothingToScroll({ type: "alternate", baseY: 0 }, "none"),
+    ).toBe(false);
+  });
+
+  it("keeps the wheel when the app reports the mouse (tmux on the normal screen)", () => {
+    for (const mode of ["x10", "vt200", "drag", "any"]) {
+      expect(wheelHasNothingToScroll({ type: "normal", baseY: 0 }, mode)).toBe(
+        false,
+      );
+    }
   });
 });