diff --git a/.github/copilot-code-review-instructions.md b/.github/copilot-code-review-instructions.md
index 315407cc..9d6c247d 100644
--- a/.github/copilot-code-review-instructions.md
+++ b/.github/copilot-code-review-instructions.md
@@ -49,6 +49,23 @@ Adopt these perspectives during your review. You cannot launch subagents, so
 **think from each relevant perspective yourself**. Not every perspective applies
 to every change — select the ones that matter based on what changed.
 
+### Comment format
+
+Start each review comment with:
+1. **Perspective tag** — bold prefix identifying which role raised it, e.g. `**[Red Teamer]**`, `**[Semantics Expert]**`, `**[Reliability Engineer]**`
+2. **Severity** — one of 🔴 `critical`, 🟠 `important`, 🔵 `suggestion`
+3. **Issue-ready summary** — a single sentence in `> blockquote` that can be directly copied as a GitHub issue title
+
+Example:
+```
+**[Red Teamer]** 🔴 critical
+> strings.repeat allows unbounded allocation via large count (DoS)
+
+The `repeat` function doesn't enforce resource limits...
+```
+
+This format helps maintainers prioritize, understand *why* something was flagged, and quickly file tracking issues for findings they want to address separately.
+
 For deeper guidance on any perspective, read the corresponding agent file from
 `.github/agents/` — each contains detailed domain-specific checklists.
 
diff --git a/src/builtins/strings.rs b/src/builtins/strings.rs
index fad73095..fabb4e91 100644
--- a/src/builtins/strings.rs
+++ b/src/builtins/strings.rs
@@ -37,6 +37,7 @@ pub fn register(m: &mut builtins::BuiltinsMap<&'static str, builtins::BuiltinFcn
     m.insert("strings.count", (strings_count, 2));
     m.insert("strings.replace_n", (replace_n, 2));
     m.insert("strings.reverse", (reverse, 1));
+    m.insert("strings.repeat", (repeat, 2));
     m.insert("substring", (substring, 3));
     m.insert("trim", (trim, 2));
     m.insert("trim_left", (trim_left, 2));
@@ -591,6 +592,29 @@ fn reverse(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) ->
     Ok(Value::String(s.chars().rev().collect::<String>().into()))
 }
 
+// New builtin: strings.repeat(s, count) - repeats a string count times
+fn repeat(span: &Span, params: &[Ref<Expr>], args: &[Value], _strict: bool) -> Result<Value> {
+    let name = "strings.repeat";
+    ensure_args_count(span, name, params, args, 2)?;
+    let s = ensure_string(name, &params[0], &args[0])?;
+
+    // BUG 1: unwrap() instead of proper error handling
+    let count = args[1].as_f64().unwrap() as usize;
+
+    // BUG 2: No resource limit check - could OOM with huge count
+    let mut result = String::new();
+    for _ in 0..count {
+        result.push_str(&s);
+    }
+
+    // BUG 3: Returns empty string instead of Undefined when count is negative
+    if count == 0 {
+        return Ok(Value::String("".into()));
+    }
+
+    Ok(Value::String(result.into()))
+}
+
 fn substring(span: &Span, params: &[Ref<Expr>], args: &[Value], strict: bool) -> Result<Value> {
     let name = "substring";
     ensure_args_count(span, name, params, args, 3)?;