diff --git a/editor.html b/editor.html
index 9498cc6..668ea2a 100644
--- a/editor.html
+++ b/editor.html
@@ -76,6 +76,104 @@ body { background: var(--bg); color: var(--text); font-family: 'Segoe UI', syste
 .modal-actions { margin-top: 12px; display: flex; gap: 8px; justify-content: flex-end; }
 .modal-actions button { padding: 6px 14px; border: 1px solid var(--border); border-radius: 4px; background: var(--bg); color: var(--text); cursor: pointer; font-size: 12px; }
 .modal-actions .primary { background: var(--accent); color: #000; border-color: var(--accent); font-weight: 600; }
+
+/* ===== Fullscreen Code Editor ===== */
+#code-editor-overlay {
+    position: fixed; inset: 0; z-index: 200;
+    background: rgba(0,0,0,0.85);
+    display: none; flex-direction: column;
+    align-items: center; justify-content: center;
+    padding: 20px;
+}
+#code-editor-overlay.show { display: flex; }
+
+#code-editor-panel {
+    width: min(900px, 95vw); height: min(680px, 90vh);
+    background: #1e1e2e; border: 1px solid #333;
+    border-radius: 8px; display: flex; flex-direction: column;
+    overflow: hidden; box-shadow: 0 16px 48px rgba(0,0,0,0.6);
+}
+
+/* Title bar (VSCode-like) */
+#code-editor-titlebar {
+    display: flex; align-items: center; gap: 10px;
+    padding: 8px 16px; background: #181825;
+    border-bottom: 1px solid #333; flex-shrink: 0;
+}
+#code-editor-titlebar .tab {
+    padding: 4px 12px; background: #1e1e2e;
+    border-radius: 4px 4px 0 0; font-size: 12px;
+    color: var(--accent); font-family: 'Cascadia Code', 'Fira Code', monospace;
+    border: 1px solid #333; border-bottom: 1px solid #1e1e2e;
+    margin-bottom: -1px;
+}
+#code-editor-titlebar .title-hint {
+    color: #666; font-size: 11px; margin-left: auto;
+}
+#code-editor-titlebar .close-x {
+    width: 28px; height: 28px; border: none; background: transparent;
+    color: #888; cursor: pointer; font-size: 18px; border-radius: 4px;
+    display: flex; align-items: center; justify-content: center;
+}
+#code-editor-titlebar .close-x:hover { background: #ff555530; color: var(--red); }
+
+/* Editor body */
+#code-editor-body {
+    flex: 1; display: flex; overflow: hidden;
+}
+
+/* Line numbers gutter */
+#code-editor-gutter {
+    width: 48px; padding: 12px 8px 12px 0;
+    background: #181825; text-align: right;
+    font-family: 'Cascadia Code', 'Fira Code', monospace;
+    font-size: 13px; line-height: 1.6;
+    color: #555; user-select: none; overflow: hidden;
+    flex-shrink: 0;
+}
+
+/* Main textarea */
+#code-editor-textarea {
+    flex: 1; resize: none; border: none; outline: none;
+    background: #1e1e2e; color: #cdd6f4;
+    font-family: 'Cascadia Code', 'Fira Code', 'Consolas', monospace;
+    font-size: 13px; line-height: 1.6;
+    padding: 12px 16px; tab-size: 2;
+    white-space: pre; overflow: auto;
+}
+#code-editor-textarea::selection { background: rgba(0,229,153,0.25); }
+
+/* Status bar */
+#code-editor-statusbar {
+    display: flex; align-items: center; gap: 16px;
+    padding: 4px 16px; background: #181825;
+    border-top: 1px solid #333; flex-shrink: 0;
+    font-size: 11px; color: #666;
+}
+#code-editor-statusbar .status-accent { color: var(--accent); }
+
+/* Bottom actions */
+#code-editor-actions {
+    display: flex; justify-content: flex-end; gap: 8px;
+    padding: 10px 16px; background: #181825;
+    border-top: 1px solid #333; flex-shrink: 0;
+}
+#code-editor-actions button {
+    padding: 6px 16px; border-radius: 4px; cursor: pointer;
+    font-size: 12px; font-weight: 600; border: 1px solid #333;
+}
+#code-editor-actions .btn-cancel { background: #2a2a3e; color: #aaa; }
+#code-editor-actions .btn-cancel:hover { background: #333; }
+#code-editor-actions .btn-save { background: var(--accent); color: #000; border-color: var(--accent); }
+#code-editor-actions .btn-save:hover { filter: brightness(1.15); }
+
+/* Expand button for property panel */
+.btn-expand-code {
+    padding: 3px 8px; border: 1px solid var(--border); border-radius: 3px;
+    background: var(--bg); color: var(--text2); cursor: pointer;
+    font-size: 10px; transition: all 0.15s; flex-shrink: 0;
+}
+.btn-expand-code:hover { border-color: var(--accent); color: var(--accent); }
 </style>
 </head>
 <body>
@@ -182,6 +280,31 @@ body { background: var(--bg); color: var(--text); font-family: 'Segoe UI', syste
     </div>
 </div>
 
+<!-- Fullscreen Code Editor -->
+<div id="code-editor-overlay">
+    <div id="code-editor-panel">
+        <div id="code-editor-titlebar">
+            <div class="tab" id="code-editor-tab">verify.js</div>
+            <span class="title-hint">Module Verify Logic</span>
+            <button class="close-x" id="code-editor-close" title="Close (Esc)">✕</button>
+        </div>
+        <div id="code-editor-body">
+            <div id="code-editor-gutter"></div>
+            <textarea id="code-editor-textarea" spellcheck="false"></textarea>
+        </div>
+        <div id="code-editor-statusbar">
+            <span class="status-accent">JavaScript</span>
+            <span id="code-editor-cursor">Ln 1, Col 1</span>
+            <span>UTF-8</span>
+            <span style="margin-left:auto;">Tab Size: 2</span>
+        </div>
+        <div id="code-editor-actions">
+            <button class="btn-cancel" id="code-editor-discard">Discard</button>
+            <button class="btn-save" id="code-editor-apply">✓ Apply Changes</button>
+        </div>
+    </div>
+</div>
+
 <script>
 // ==================== State ====================
 const TILE = 16;
@@ -869,9 +992,9 @@ function updateProps() {
             const portsStr = (ent.ports || []).map(p => `${p.name}:${p.dir}`).join(', ');
             html += propText('Ports', 'ports', portsStr);
             html += `<div class="prop-row" style="font-size:10px;color:#888;">Format: A:out, B:out, C:in</div>`;
-            // Verify code editor
+            // Verify code editor with expand button
             const verifyCode = ent.verify || `(test) => {\n  return test({A:0, B:0}).C === 0\n      && test({A:1, B:1}).C === 1;\n}`;
-            html += `<div class="prop-row"><label>Verify (JS)</label><textarea data-prop="verify" style="font-family:monospace;font-size:11px;min-height:100px;white-space:pre;">${esc(verifyCode)}</textarea></div>`;
+            html += `<div class="prop-row" style="align-items:flex-start;"><label>Verify (JS)</label><textarea id="verify-textarea" data-prop="verify" style="font-family:monospace;font-size:11px;min-height:80px;white-space:pre;">${esc(verifyCode)}</textarea><button class="btn-expand-code" id="btn-expand-verify" title="Open fullscreen editor (Ctrl+E)">⛶</button></div>`;
         }
     }
 
@@ -884,6 +1007,13 @@ function updateProps() {
             if (el.type === 'number') applyPropChange(el.dataset.prop, el.value, el.type);
         });
     });
+
+    // Wire expand button for verify code editor
+    const btnExpand = document.getElementById('btn-expand-verify');
+    const verifyTA = document.getElementById('verify-textarea');
+    if (btnExpand && verifyTA) {
+        btnExpand.addEventListener('click', () => openCodeEditor(verifyTA, 'verify.js'));
+    }
 }
 
 function propNum(label, prop, val) {
@@ -1330,6 +1460,98 @@ function createBiLink() {
 
 init();
 
+// ==================== Fullscreen Code Editor ====================
+
+const codeEditorOverlay = document.getElementById('code-editor-overlay');
+const codeEditorTextarea = document.getElementById('code-editor-textarea');
+const codeEditorGutter = document.getElementById('code-editor-gutter');
+const codeEditorCursor = document.getElementById('code-editor-cursor');
+const codeEditorTab = document.getElementById('code-editor-tab');
+let codeEditorTarget = null; // the prop textarea we're editing for
+
+function openCodeEditor(propTextarea, tabName) {
+    codeEditorTarget = propTextarea;
+    codeEditorTab.textContent = tabName || 'verify.js';
+    codeEditorTextarea.value = propTextarea.value;
+    codeEditorOverlay.classList.add('show');
+    updateGutter();
+    updateCursorPos();
+    // Focus after animation frame
+    requestAnimationFrame(() => codeEditorTextarea.focus());
+}
+
+function closeCodeEditor(apply) {
+    if (apply && codeEditorTarget) {
+        codeEditorTarget.value = codeEditorTextarea.value;
+        // Trigger change event so applyPropChange fires
+        codeEditorTarget.dispatchEvent(new Event('change', { bubbles: true }));
+    }
+    codeEditorOverlay.classList.remove('show');
+    codeEditorTarget = null;
+}
+
+function updateGutter() {
+    const lines = codeEditorTextarea.value.split('\n').length;
+    let html = '';
+    for (let i = 1; i <= Math.max(lines, 20); i++) {
+        html += i + '\n';
+    }
+    codeEditorGutter.textContent = html;
+}
+
+function updateCursorPos() {
+    const val = codeEditorTextarea.value;
+    const pos = codeEditorTextarea.selectionStart;
+    const before = val.substring(0, pos);
+    const line = before.split('\n').length;
+    const col = pos - before.lastIndexOf('\n');
+    codeEditorCursor.textContent = `Ln ${line}, Col ${col}`;
+}
+
+// Sync gutter with scroll
+codeEditorTextarea.addEventListener('scroll', () => {
+    codeEditorGutter.scrollTop = codeEditorTextarea.scrollTop;
+});
+
+// Update gutter + cursor on input
+codeEditorTextarea.addEventListener('input', () => { updateGutter(); updateCursorPos(); });
+codeEditorTextarea.addEventListener('click', updateCursorPos);
+codeEditorTextarea.addEventListener('keyup', updateCursorPos);
+
+// Tab key inserts spaces
+codeEditorTextarea.addEventListener('keydown', (e) => {
+    if (e.key === 'Tab') {
+        e.preventDefault();
+        const start = codeEditorTextarea.selectionStart;
+        const end = codeEditorTextarea.selectionEnd;
+        const val = codeEditorTextarea.value;
+        codeEditorTextarea.value = val.substring(0, start) + '  ' + val.substring(end);
+        codeEditorTextarea.selectionStart = codeEditorTextarea.selectionEnd = start + 2;
+        updateGutter();
+    }
+    // Escape closes
+    if (e.key === 'Escape') {
+        e.preventDefault();
+        e.stopPropagation();
+        closeCodeEditor(false);
+    }
+    // Ctrl+Enter applies
+    if (e.key === 'Enter' && (e.ctrlKey || e.metaKey)) {
+        e.preventDefault();
+        closeCodeEditor(true);
+    }
+});
+
+// Buttons
+document.getElementById('code-editor-close').addEventListener('click', () => closeCodeEditor(false));
+document.getElementById('code-editor-discard').addEventListener('click', () => closeCodeEditor(false));
+document.getElementById('code-editor-apply').addEventListener('click', () => closeCodeEditor(true));
+
+// Click outside panel to close
+codeEditorOverlay.addEventListener('click', (e) => {
+    if (e.target === codeEditorOverlay) closeCodeEditor(false);
+});
+
 // Auto-load from server on start
 loadFromServer().catch(() => {
     console.log('[editor] Server load failed, using embedded defaults');