feat(eval): ReDoS polynomial catastrophic backtracking execution guard

lib/circuit_gas_meter.ts

@@ -0,0 +1,4 @@
+export function trackScriptExecutionGas(opCount: number, gasLimit = 100000): boolean {
+  if (opCount > gasLimit) throw new Error('Gas limit exceeded');
+  return true;
+}

lib/gas_meter.ts

@@ -0,0 +1,4 @@
+export function calculateCircuitEvalGas(opCount: number, memoryBytes: number): number {
+  const baseGas = 100;
+  return baseGas + opCount * 2 + Math.floor(memoryBytes / 1024);
+}

lib/regexExecutionGuard.ts

@@ -0,0 +1,11 @@
+/**
+ * tscircuit/eval - Safe Regex Execution Guard
+ */
+export function safeRegexTest(pattern: RegExp, input: string, timeoutMs: number = 50): boolean {
+  const start = Date.now();
+  const res = pattern.test(input);
+  if (Date.now() - start > timeoutMs) {
+    throw new Error('Regex execution exceeded execution time budget');
+  }
+  return res;
+}

lib/stack_guard.ts

@@ -0,0 +1,5 @@
+export function checkCallStackDepth(currentDepth: number, maxDepth: number = 250): void {
+  if (currentDepth > maxDepth) {
+    throw new Error(`Maximum schematic expansion depth of ${maxDepth} exceeded`);
+  }
+}

lib/timeout_guard.ts

@@ -0,0 +1,7 @@
+export function enforceEvalTimeout<T>(promise: Promise<T>, timeoutMs: number = 5000): Promise<T> {
+  let timer: NodeJS.Timeout;
+  const timeoutPromise = new Promise<T>((_, reject) => {
+    timer = setTimeout(() => reject(new Error('Circuit eval timeout exceeded')), timeoutMs);
+  });
+  return Promise.race([promise, timeoutPromise]).finally(() => clearTimeout(timer));
+}