diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 0000000..c6f87f2
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 2024-10-30 - Command Injection in Syntax Checker
+**Vulnerability:** Use of string-based \`execSync\` for node syntax checking (\`execSync(\\\`node --check "\${tempFile}"\\\`)\`) allows for potential command injection if \`tempFile\` path can be manipulated.
+**Learning:** Even internal tool execution or paths that seem controlled should use array-based argument passing (e.g., \`spawnSync\`) and \`process.execPath\` to absolutely prevent injection vulnerabilities in execution engines.
+**Prevention:** Always prefer \`spawnSync\` over \`execSync\`, use \`process.execPath\` for invoking node, and pass arguments as an array rather than constructing a command string.
diff --git a/packages/core/src/reconcile.ts b/packages/core/src/reconcile.ts
index b0285bc..482624f 100644
--- a/packages/core/src/reconcile.ts
+++ b/packages/core/src/reconcile.ts
@@ -1,4 +1,4 @@
-import { execSync } from "node:child_process";
+import { spawnSync } from "node:child_process";
 import crypto from "node:crypto";
 import fs from "node:fs";
 import path from "node:path";
@@ -139,7 +139,13 @@ export function reconcile(options: ReconcileOptions): ReconcileResult {
   fs.writeFileSync(tempFile, extractedCode, "utf8");
 
   try {
-    execSync(`node --check "${tempFile}"`, { stdio: "pipe" });
+    const result = spawnSync(process.execPath, ["--check", tempFile], { stdio: "pipe" });
+    if (result.error) throw result.error;
+    if (result.status !== 0) {
+      const err = new Error("Syntax check failed") as Error & { stderr: Buffer };
+      err.stderr = result.stderr;
+      throw err;
+    }
     log.audit("Syntax check passed");
   } catch (err) {
     const stderr =