refactor: remove ALL custom paste handlers — clean slate per COE review

After 9 clipboard commits that kept breaking each other, COE review
determined: ttyd uses ClipboardAddon, not custom handlers. Ctrl+Shift+V
on Linux and Cmd+V on macOS both trigger native browser paste events
that xterm.js catches via its hidden textarea handler. Zero custom
paste code needed. Deleted synthetic ClipboardEvent dispatch, readText
calls, and all paste-related comments. Kept: Ctrl+Shift+C copy,
auto-copy on selection, OSC 52, Ctrl+F search.

muxplex/frontend/terminal.js

@@ -364,13 +364,9 @@ function openTerminal(sessionName, remoteId) {
   _term.open(container);
 
   // --- Clipboard integration ---
-  // Ctrl+Shift+C: copy selection to system clipboard (Ctrl+C still sends SIGINT)
-  // Ctrl+Shift+V: Ctrl+Shift+V does NOT trigger a native browser paste event (unlike Cmd+V
-  //   on macOS). We read the clipboard via navigator.clipboard.readText() and dispatch a
-  //   synthetic ClipboardEvent on xterm.js's hidden textarea. xterm.js catches this via its
-  //   built-in handlePasteEvent listener → prepareTextForTerminal → bracketTextForPaste
-  //   → triggerDataEvent → onData → WebSocket. This is the same path as Cmd+V and correctly
-  //   handles CR/LF normalization, bracketed paste mode, and UTF-8 encoding.
+  // Copy: Ctrl+Shift+C intercepts and copies selection to system clipboard
+  // Paste: handled natively by xterm.js (browser paste event → hidden textarea → onData → WebSocket)
+  //   Cmd+V (macOS) and Ctrl+Shift+V (Linux) both trigger native browser paste events
   _term.attachCustomKeyEventHandler(function(e) {
     if (e.type !== 'keydown') return true;
 
@@ -381,24 +377,6 @@ function openTerminal(sessionName, remoteId) {
       return false;  // prevent xterm from processing
     }
 
-    // Ctrl+Shift+V → paste from system clipboard via synthetic ClipboardEvent on xterm textarea.
-    // Dispatching on _term.textarea triggers xterm.js's built-in handlePasteEvent, which
-    // handles CR/LF normalization, bracketed paste mode, and correct UTF-8 encoding —
-    // the exact same code path as a native Cmd+V paste on macOS.
-    if (e.ctrlKey && e.shiftKey && (e.key === 'V' || e.code === 'KeyV')) {
-      if (navigator.clipboard && navigator.clipboard.readText && _term && _term.textarea) {
-        navigator.clipboard.readText().then(function(text) {
-          if (!text || !_term || !_term.textarea) return;
-          var pasteEvent = new ClipboardEvent('paste', {
-            clipboardData: new DataTransfer(),
-          });
-          pasteEvent.clipboardData.setData('text/plain', text);
-          _term.textarea.dispatchEvent(pasteEvent);
-        }).catch(function() {});
-      }
-      return false;  // prevent xterm from processing the raw key
-    }
-
     // Ctrl+F → open search bar
     if (e.ctrlKey && !e.shiftKey && (e.key === 'f' || e.key === 'F' || e.code === 'KeyF')) {
       _openSearch();

muxplex/frontend/tests/test_terminal.mjs

@@ -993,25 +993,22 @@ test('terminal.js loads xterm-addon-image for inline graphics', () => {
   assert.ok(source.includes('ImageAddon'), 'must reference ImageAddon');
 });
 
-// --- Ctrl+Shift+V: synthetic paste event on xterm textarea ---
+// --- Ctrl+Shift+V: xterm.js handles paste natively, no custom interception ---
 
-test('terminal.js Ctrl+Shift+V dispatches synthetic paste event on textarea', () => {
-  // Ctrl+Shift+V does NOT trigger a native browser paste event (unlike Cmd+V on macOS).
-  // Fix: read clipboard via navigator.clipboard.readText(), then dispatch a synthetic
-  // ClipboardEvent on xterm.js's hidden textarea. This goes through xterm.js's built-in
-  // handlePasteEvent which handles CR/LF normalization, bracketed paste, and correct encoding.
+test('terminal.js does NOT intercept Ctrl+Shift+V in attachCustomKeyEventHandler', () => {
+  // COE review: every custom paste handler we built caused either double-paste or encoding issues.
+  // On Linux, Ctrl+Shift+V is a native browser paste shortcut — it fires a paste event on the
+  // focused textarea, xterm.js catches it natively. On macOS, Cmd+V does the same.
+  // Zero custom paste code needed.
   const source = fs.readFileSync(new URL('../terminal.js', import.meta.url), 'utf8');
   const handlerStart = source.indexOf('attachCustomKeyEventHandler');
-  const handlerEnd = source.indexOf('// Auto-copy:', handlerStart);
+  const handlerEnd = source.indexOf('onSelectionChange', handlerStart);
   const handlerBlock = source.substring(handlerStart, handlerEnd);
-  assert.ok(
-    handlerBlock.includes("e.key === 'V'") || handlerBlock.includes("e.code === 'KeyV'"),
-    'attachCustomKeyEventHandler must intercept Ctrl+Shift+V to trigger paste',
-  );
-  assert.ok(
-    handlerBlock.includes('ClipboardEvent') || handlerBlock.includes('dispatchEvent'),
-    'must dispatch synthetic paste event so xterm.js handlePasteEvent handles encoding correctly',
-  );
+  // Must NOT have any V key interception
+  assert.ok(!handlerBlock.includes("e.key === 'V'"),
+    'must NOT intercept Ctrl+Shift+V — xterm.js handles paste natively via browser events');
+  assert.ok(!handlerBlock.includes("e.code === 'KeyV'"),
+    'must NOT intercept KeyV — xterm.js handles paste natively via browser events');
 });
 
 // --- UTF-8 output decoding via TextDecoder ---