diff --git a/app/templates/recipes/detail.html b/app/templates/recipes/detail.html
index 3c6843a..daf134a 100644
--- a/app/templates/recipes/detail.html
+++ b/app/templates/recipes/detail.html
@@ -116,12 +116,86 @@
     <h2 class="text-lg font-semibold mb-4">Recipe (S-expression)</h2>
     <div class="bg-gray-900 rounded-lg p-4 border border-gray-700">
         {% if recipe.sexp %}
-        <pre class="text-sm font-mono text-gray-300 overflow-x-auto whitespace-pre-wrap">{{ recipe.sexp }}</pre>
+        <pre class="text-sm font-mono text-gray-300 overflow-x-auto whitespace-pre-wrap sexp-code">{{ recipe.sexp }}</pre>
         {% else %}
         <p class="text-gray-500">No source available</p>
         {% endif %}
     </div>
 
+    <script>
+    // Single-pass S-expression syntax highlighter (avoids regex corruption)
+    function highlightSexp(text) {
+        const SPECIAL = new Set(['plan','recipe','def','->','stream','let','lambda','if','cond','define']);
+        const PRIMS = new Set(['source','effect','sequence','segment','resize','transform','layer','blend','mux','analyze','fused-pipeline']);
+        function esc(s) { return s.replace(/&/g,'&amp;').replace(/</g,'&lt;').replace(/>/g,'&gt;'); }
+        function span(cls, s) { return '<span class="' + cls + '">' + esc(s) + '</span>'; }
+
+        let out = '', i = 0, len = text.length;
+        while (i < len) {
+            if (text[i] === ';' && i + 1 < len && text[i+1] === ';') {
+                let end = text.indexOf('\n', i);
+                if (end === -1) end = len;
+                out += span('text-gray-500', text.slice(i, end));
+                i = end;
+            }
+            else if (text[i] === '"') {
+                let j = i + 1;
+                while (j < len && text[j] !== '"') { if (text[j] === '\\') j++; j++; }
+                if (j < len) j++;
+                out += span('text-green-400', text.slice(i, j));
+                i = j;
+            }
+            else if (text[i] === ':' && i + 1 < len && /[a-zA-Z_-]/.test(text[i+1])) {
+                let j = i + 1;
+                while (j < len && /[a-zA-Z0-9_-]/.test(text[j])) j++;
+                out += span('text-purple-400', text.slice(i, j));
+                i = j;
+            }
+            else if (text[i] === '(') {
+                out += span('text-yellow-500', '(');
+                i++;
+                let ws = '';
+                while (i < len && (text[i] === ' ' || text[i] === '\t')) { ws += text[i]; i++; }
+                out += esc(ws);
+                if (i < len && /[a-zA-Z_>-]/.test(text[i])) {
+                    let j = i;
+                    while (j < len && /[a-zA-Z0-9_>-]/.test(text[j])) j++;
+                    let word = text.slice(i, j);
+                    if (SPECIAL.has(word)) out += span('text-pink-400 font-semibold', word);
+                    else if (PRIMS.has(word)) out += span('text-blue-400', word);
+                    else out += esc(word);
+                    i = j;
+                }
+            }
+            else if (text[i] === ')') {
+                out += span('text-yellow-500', ')');
+                i++;
+            }
+            else if (/[0-9]/.test(text[i]) && (i === 0 || /[\s(]/.test(text[i-1]))) {
+                let j = i;
+                while (j < len && /[0-9.]/.test(text[j])) j++;
+                out += span('text-orange-300', text.slice(i, j));
+                i = j;
+            }
+            else {
+                let j = i;
+                while (j < len && !'(;":)'.includes(text[j])) {
+                    if (text[j] === ':' && j + 1 < len && /[a-zA-Z_-]/.test(text[j+1])) break;
+                    if (/[0-9]/.test(text[j]) && (j === 0 || /[\s(]/.test(text[j-1]))) break;
+                    j++;
+                }
+                if (j === i) { out += esc(text[i]); i++; }
+                else { out += esc(text.slice(i, j)); i = j; }
+            }
+        }
+        return out;
+    }
+
+    document.querySelectorAll('.sexp-code').forEach(el => {
+        el.innerHTML = highlightSexp(el.textContent);
+    });
+    </script>
+
     <!-- Actions -->
     <div class="flex items-center space-x-4 mt-8">
         <button hx-post="/runs/rerun/{{ recipe.recipe_id }}"
diff --git a/app/templates/runs/detail.html b/app/templates/runs/detail.html
index c7abb2d..ae87dd3 100644
--- a/app/templates/runs/detail.html
+++ b/app/templates/runs/detail.html
@@ -550,23 +550,85 @@
         }
         </style>
         <script>
-        // Syntax highlight S-expressions
+        // Single-pass S-expression syntax highlighter (avoids regex corruption)
+        function highlightSexp(text) {
+            const SPECIAL = new Set(['plan','recipe','def','->','stream','let','lambda','if','cond','define']);
+            const PRIMS = new Set(['source','effect','sequence','segment','resize','transform','layer','blend','mux','analyze','fused-pipeline']);
+            function esc(s) { return s.replace(/&/g,'&amp;').replace(/</g,'&lt;').replace(/>/g,'&gt;'); }
+            function span(cls, s) { return '<span class="' + cls + '">' + esc(s) + '</span>'; }
+
+            let out = '', i = 0, len = text.length;
+            while (i < len) {
+                // Comments
+                if (text[i] === ';' && i + 1 < len && text[i+1] === ';') {
+                    let end = text.indexOf('\n', i);
+                    if (end === -1) end = len;
+                    out += span('text-gray-500', text.slice(i, end));
+                    i = end;
+                }
+                // Strings
+                else if (text[i] === '"') {
+                    let j = i + 1;
+                    while (j < len && text[j] !== '"') { if (text[j] === '\\') j++; j++; }
+                    if (j < len) j++; // closing quote
+                    out += span('text-green-400', text.slice(i, j));
+                    i = j;
+                }
+                // Keywords (:keyword)
+                else if (text[i] === ':' && i + 1 < len && /[a-zA-Z_-]/.test(text[i+1])) {
+                    let j = i + 1;
+                    while (j < len && /[a-zA-Z0-9_-]/.test(text[j])) j++;
+                    out += span('text-purple-400', text.slice(i, j));
+                    i = j;
+                }
+                // Open paren - check for primitive/special after it
+                else if (text[i] === '(') {
+                    out += span('text-yellow-500', '(');
+                    i++;
+                    // Skip whitespace after paren
+                    let ws = '';
+                    while (i < len && (text[i] === ' ' || text[i] === '\t')) { ws += text[i]; i++; }
+                    out += esc(ws);
+                    // Check if next word is a special form or primitive
+                    if (i < len && /[a-zA-Z_>-]/.test(text[i])) {
+                        let j = i;
+                        while (j < len && /[a-zA-Z0-9_>-]/.test(text[j])) j++;
+                        let word = text.slice(i, j);
+                        if (SPECIAL.has(word)) out += span('text-pink-400 font-semibold', word);
+                        else if (PRIMS.has(word)) out += span('text-blue-400', word);
+                        else out += esc(word);
+                        i = j;
+                    }
+                }
+                // Close paren
+                else if (text[i] === ')') {
+                    out += span('text-yellow-500', ')');
+                    i++;
+                }
+                // Numbers
+                else if (/[0-9]/.test(text[i]) && (i === 0 || /[\s(]/.test(text[i-1]))) {
+                    let j = i;
+                    while (j < len && /[0-9.]/.test(text[j])) j++;
+                    out += span('text-orange-300', text.slice(i, j));
+                    i = j;
+                }
+                // Regular text
+                else {
+                    let j = i;
+                    while (j < len && !'(;":)'.includes(text[j])) {
+                        if (text[j] === ':' && j + 1 < len && /[a-zA-Z_-]/.test(text[j+1])) break;
+                        if (/[0-9]/.test(text[j]) && (j === 0 || /[\s(]/.test(text[j-1]))) break;
+                        j++;
+                    }
+                    if (j === i) { out += esc(text[i]); i++; } // safety: advance at least 1 char
+                    else { out += esc(text.slice(i, j)); i = j; }
+                }
+            }
+            return out;
+        }
+
         document.querySelectorAll('.sexp-code').forEach(el => {
-            let html = el.textContent;
-            // Comments
-            html = html.replace(/(;;.*)/g, '<span class="text-gray-500">$1</span>');
-            // Keywords (:keyword)
-            html = html.replace(/(:[a-zA-Z_-]+)/g, '<span class="text-purple-400">$1</span>');
-            // Strings
-            html = html.replace(/("(?:[^"\\]|\\.)*")/g, '<span class="text-green-400">$1</span>');
-            // Special forms
-            html = html.replace(/\b(plan|recipe|def|->)\b/g, '<span class="text-pink-400 font-semibold">$1</span>');
-            // Primitives
-            html = html.replace(/\((source|effect|sequence|segment|resize|transform|layer|blend|mux|analyze)\b/g,
-                '(<span class="text-blue-400">$1</span>');
-            // Parentheses
-            html = html.replace(/(\(|\))/g, '<span class="text-yellow-500">$1</span>');
-            el.innerHTML = html;
+            el.innerHTML = highlightSexp(el.textContent);
         });
         </script>
         {% else %}