feat: auto-copy mouse selection + OSC 52 tmux clipboard bridge

Mouse selection: onSelectionChange auto-copies to system clipboard on
every selection change (last fire on mouse-up captures final text).
Matches iTerm2/WezTerm/ttyd native select-to-copy behavior.

OSC 52: Custom parser.registerOscHandler(52, ...) decodes base64
clipboard data from tmux. When tmux copies text (set-clipboard on
in .tmux.conf), it sends OSC 52 to the terminal. We intercept and
write to system clipboard via _copyToClipboard (with execCommand
fallback for HTTP/LAN contexts).

Together: mouse-select auto-copies, and tmux Ctrl+B [ -> select ->
Enter copies to system clipboard via OSC 52.

muxplex/frontend/terminal.js

@@ -312,6 +312,36 @@ function openTerminal(sessionName, sourceUrl) {
     return true;  // let xterm handle all other keys normally
   });
 
+  // Auto-copy: when mouse selection ends, copy to system clipboard.
+  // Matches terminal emulator conventions (iTerm2, WezTerm, ttyd native).
+  // onSelectionChange fires whenever selection changes — copy if text is selected.
+  // When selection is cleared (empty string), we skip the clipboard write.
+  _term.onSelectionChange(function() {
+    var sel = _term.getSelection();
+    if (sel) {
+      _copyToClipboard(sel);
+    }
+  });
+
+  // OSC 52 clipboard integration — bridges tmux clipboard to the browser.
+  // When tmux copies text (with `set-clipboard on` in .tmux.conf), it sends
+  // an OSC 52 escape sequence to the terminal. xterm.js surfaces this via the
+  // parser API. We intercept and write the decoded text to the system clipboard
+  // so that: Ctrl+B [ → select → Enter (tmux copy) → system clipboard receives it.
+  _term.parser.registerOscHandler(52, function(data) {
+    // OSC 52 format: Pc ; Pd — Pc = selection target (c/p/q/s/0-7), Pd = base64 text
+    var parts = data.split(';');
+    if (parts.length >= 2) {
+      try {
+        var text = atob(parts[1]);
+        _copyToClipboard(text);
+      } catch (e) {
+        // Invalid base64 or unsupported — silently ignore
+      }
+    }
+    return true;  // Handled — don't pass to xterm's default handler
+  });
+
   if (_fitAddon) {
     // requestAnimationFrame guarantees one full browser layout pass after the flex
     // container becomes visible before fit() measures dimensions.

muxplex/frontend/tests/test_terminal.mjs

@@ -49,6 +49,8 @@ function loadTerminal() {
     focus: () => { focusCallCount++; },
     attachCustomKeyEventHandler: () => {},
     getSelection: () => '',
+    onSelectionChange: () => {},
+    parser: { registerOscHandler: () => {} },
   };
 
   // Capture all messages sent via WebSocket.send()
@@ -335,6 +337,8 @@ function createMultiSessionEnv() {
       focus: () => {},
       attachCustomKeyEventHandler: () => {},
       getSelection: () => '',
+      onSelectionChange: () => {},
+      parser: { registerOscHandler: () => {} },
       writeMessages: [],
     };
     t.write = (data) => t.writeMessages.push(data);
@@ -921,4 +925,28 @@ test('_setTerminalFontSize sets _term.options.fontSize and calls _fitAddon.fit()
   );
 });
 
+// --- Clipboard Issue 1: auto-copy mouse selection via onSelectionChange ---
+
+test('terminal.js auto-copies mouse selection to clipboard via onSelectionChange', () => {
+  const source = fs.readFileSync(new URL('../terminal.js', import.meta.url), 'utf8');
+  assert.ok(
+    source.includes('onSelectionChange'),
+    'must register onSelectionChange handler to auto-copy mouse selection to clipboard',
+  );
+});
+
+// --- Clipboard Issue 2: OSC 52 handler bridges tmux clipboard to browser ---
+
+test('terminal.js registers OSC 52 handler for tmux clipboard bridge', () => {
+  const source = fs.readFileSync(new URL('../terminal.js', import.meta.url), 'utf8');
+  assert.ok(
+    source.includes('registerOscHandler'),
+    'must call parser.registerOscHandler to intercept tmux OSC 52 clipboard sequences',
+  );
+  assert.ok(
+    source.includes('atob'),
+    'must decode base64 OSC 52 clipboard payload with atob()',
+  );
+});
+