diff --git a/apps/web/src/components/features/terminal/terminal.tsx b/apps/web/src/components/features/terminal/terminal.tsx
index 6ffd0c5..f518fb7 100644
--- a/apps/web/src/components/features/terminal/terminal.tsx
+++ b/apps/web/src/components/features/terminal/terminal.tsx
@@ -387,11 +387,38 @@ export const TerminalComponent = React.forwardRef<TerminalRef, TerminalProps>(
 					scrollPending = 0;
 				};
 
-				const isAlternateScreen = () => {
-					const term = termRef.current;
-					if (!term) return false;
-					return term.buffer.active === term.buffer.alternate;
-				};
+			const isAlternateScreen = () => {
+				const term = termRef.current;
+				if (!term) return false;
+				return term.buffer.active === term.buffer.alternate;
+			};
+
+			// Debug overlay for mobile scroll diagnostics
+			let debugOverlay: HTMLDivElement | null = null;
+			const showDebug = (msg: string) => {
+				if (!debugOverlay) {
+					debugOverlay = document.createElement("div");
+					debugOverlay.style.position = "fixed";
+					debugOverlay.style.bottom = "120px";
+					debugOverlay.style.left = "8px";
+					debugOverlay.style.right = "8px";
+					debugOverlay.style.zIndex = "9999";
+					debugOverlay.style.background = "rgba(0,0,0,0.8)";
+					debugOverlay.style.color = "#0f0";
+					debugOverlay.style.fontFamily = "monospace";
+					debugOverlay.style.fontSize = "11px";
+					debugOverlay.style.padding = "8px";
+					debugOverlay.style.borderRadius = "6px";
+					debugOverlay.style.pointerEvents = "none";
+					debugOverlay.style.whiteSpace = "pre-wrap";
+					debugOverlay.style.maxHeight = "120px";
+					debugOverlay.style.overflow = "auto";
+					document.body.appendChild(debugOverlay);
+				}
+				const line = `${new Date().toLocaleTimeString()} ${msg}`;
+				debugOverlay.textContent =
+					line + "\n" + debugOverlay.textContent?.split("\n").slice(0, 8).join("\n");
+			};
 
 				const onTouchStart = (e: TouchEvent) => {
 					if (e.touches.length === 1) {
@@ -406,6 +433,10 @@ export const TerminalComponent = React.forwardRef<TerminalRef, TerminalProps>(
 					const touch = e.touches[0];
 					const deltaY = startY - touch.clientY;
 					const deltaX = Math.abs(startX - touch.clientX);
+					const alternate = isAlternateScreen();
+					showDebug(
+						`move dy=${deltaY.toFixed(0)} dx=${deltaX.toFixed(0)} alt=${alternate} scrolling=${isScrolling}`,
+					);
 
 					// Decide early whether this is a vertical scroll gesture.
 					if (!isScrolling) {
@@ -418,10 +449,11 @@ export const TerminalComponent = React.forwardRef<TerminalRef, TerminalProps>(
 					// Take over the gesture so the page/toolbar never scrolls.
 					e.preventDefault();
 
-					if (isAlternateScreen()) {
+					if (alternate) {
 						// Alternate screen (tmux/vim): accumulate the swipe and
 						// send SGR 1006 mouse-wheel events in steps.
 						scrollPending += deltaY;
+						showDebug(`alt pending=${scrollPending.toFixed(0)}`);
 						flushScroll();
 					} else if (termRef.current) {
 						// Normal buffer: let xterm.js scroll its own viewport by
@@ -431,6 +463,7 @@ export const TerminalComponent = React.forwardRef<TerminalRef, TerminalProps>(
 								? (termRef.current.options.fontSize as number) * 1.2
 								: 10;
 						const lines = Math.round(deltaY / lineHeight);
+						showDebug(`normal lines=${lines}`);
 						if (lines !== 0) {
 							termRef.current.scrollLines(lines);
 						}