Fix mouse wheel scrolling to use tmux copy-mode instead of sending arrow keys to shell

src/client/components/Terminal.tsx

@@ -549,22 +549,16 @@ export default function Terminal({
       const currentSessionId = sessionIdRef.current
       if (!currentSessionId || lines === 0) return false
 
-      const terminal = terminalRef.current
-      const cols = terminal?.cols ?? 80
-      const rows = terminal?.rows ?? 24
-      const col = Math.floor(cols / 2)
-      const row = Math.floor(rows / 2)
-
-      // SGR mouse wheel: button 64 = scroll up, 65 = scroll down
-      const button = lines > 0 ? 65 : 64
-      const count = Math.abs(lines)
       const scrolledUp = lines < 0
+      const count = Math.abs(lines)
 
+      // Send tmux scroll command directly to enter copy-mode and scroll
       for (let i = 0; i < count; i++) {
         sendMessageRef.current({
-          type: 'terminal-input',
+          type: 'tmux-scroll',
           sessionId: currentSessionId,
-          data: `\x1b[<${button};${col};${row}M`
+          direction: lines > 0 ? 'down' : 'up',
+          lines: 1
         })
       }
 

src/client/hooks/useTerminal.ts

@@ -510,26 +510,20 @@ export function useTerminal({
       const STEP = 30
       wheelAccumRef.current += ev.deltaY
 
-      // Get approximate cell position for SGR mouse event
-      const cols = terminal.cols
-      const rows = terminal.rows
-      const col = Math.floor(cols / 2)
-      const row = Math.floor(rows / 2)
-
       let scrolledUp = false
       let didScroll = false
       while (Math.abs(wheelAccumRef.current) >= STEP) {
         didScroll = true
         const down = wheelAccumRef.current > 0
         wheelAccumRef.current += down ? -STEP : STEP
 
-        // SGR mouse wheel: button 64 = scroll up, 65 = scroll down
-        const button = down ? 65 : 64
+        // Send tmux scroll command directly to enter copy-mode and scroll
         if (!down) scrolledUp = true
         sendMessageRef.current({
-          type: 'terminal-input',
+          type: 'tmux-scroll',
           sessionId: attached,
-          data: `\x1b[<${button};${col};${row}M`
+          direction: down ? 'down' : 'up',
+          lines: 1
         })
       }
 

src/server/index.ts

@@ -1031,6 +1031,9 @@ function handleMessage(
     case 'tmux-check-copy-mode':
       handleCheckCopyMode(message.sessionId, ws)
       return
+    case 'tmux-scroll':
+      handleTmuxScroll(message.sessionId, message.direction, message.lines, ws)
+      return
     case 'session-resume':
       handleSessionResume(message, ws)
       return
@@ -1091,6 +1094,71 @@ function handleCheckCopyMode(sessionId: string, ws: ServerWebSocket<WSData>) {
   }
 }
 
+function handleTmuxScroll(
+  sessionId: string,
+  direction: 'up' | 'down',
+  lines: number,
+  ws: ServerWebSocket<WSData>
+) {
+  const session = registry.get(sessionId)
+  if (!session) return
+  if (session.remote) return
+
+  try {
+    const target = resolveCopyModeTarget(sessionId, ws, session)
+
+    // Enter copy-mode if not already in it
+    Bun.spawnSync(['tmux', 'copy-mode', '-t', target], {
+      stdout: 'ignore',
+      stderr: 'ignore',
+    })
+
+    // Scroll in copy-mode using tmux's native scroll commands
+    const scrollCmd = direction === 'up' ? 'scroll-up' : 'scroll-down'
+    Bun.spawnSync(
+      ['tmux', 'send-keys', '-X', '-t', target, '-N', lines.toString(), scrollCmd],
+      {
+        stdout: 'ignore',
+        stderr: 'ignore',
+      }
+    )
+
+    // When scrolling down, check if we've reached the bottom (scroll position 0)
+    // If so, explicitly exit copy-mode
+    if (direction === 'down') {
+      const scrollPosResult = Bun.spawnSync(
+        ['tmux', 'display-message', '-p', '-t', target, '#{scroll_position}'],
+        { stdout: 'pipe', stderr: 'ignore' }
+      )
+      const scrollPosition = Number.parseInt(scrollPosResult.stdout.toString().trim(), 10)
+
+      // At position 0 (bottom), exit copy-mode automatically
+      if (scrollPosition === 0) {
+        Bun.spawnSync(['tmux', 'send-keys', '-X', '-t', target, 'cancel'], {
+          stdout: 'ignore',
+          stderr: 'ignore',
+        })
+      }
+    }
+
+    // Check copy-mode status after scrolling
+    const checkResult = Bun.spawnSync(
+      ['tmux', 'display-message', '-p', '-t', target, '#{pane_in_mode}'],
+      { stdout: 'pipe', stderr: 'ignore' }
+    )
+    const inCopyMode = checkResult.stdout.toString().trim() === '1'
+
+    // Report current copy-mode status to client
+    send(ws, {
+      type: 'tmux-copy-mode-status',
+      sessionId,
+      inCopyMode,
+    })
+  } catch {
+    // Silently ignore scroll errors
+  }
+}
+
 function handleKill(sessionId: string, ws: ServerWebSocket<WSData>) {
   const session = registry.get(sessionId)
   if (!session) {

src/shared/types.ts

@@ -115,6 +115,7 @@ export type ClientMessage =
   | { type: 'terminal-detach'; sessionId: string }
   | { type: 'terminal-input'; sessionId: string; data: string }
   | { type: 'terminal-resize'; sessionId: string; cols: number; rows: number }
+  | { type: 'tmux-scroll'; sessionId: string; direction: 'up' | 'down'; lines: number }
   | { type: 'session-create'; projectPath: string; name?: string; command?: string }
   | { type: 'session-kill'; sessionId: string }
   | { type: 'session-rename'; sessionId: string; newName: string }