diff --git a/vibn-agent-runner/src/agent-session-runner.ts b/vibn-agent-runner/src/agent-session-runner.ts
index 8dc69f1..9f0fe06 100644
--- a/vibn-agent-runner/src/agent-session-runner.ts
+++ b/vibn-agent-runner/src/agent-session-runner.ts
@@ -15,6 +15,50 @@ import { resolvePrompt } from "./prompts/loader";
 
 const MAX_TURNS = 45;
 
+function runBuildVerification(
+  repoRoot: string,
+  appPath: string,
+): { success: boolean; error?: string } {
+  const fs = require("fs") as typeof import("fs");
+  const path = require("path") as typeof import("path");
+  const { execSync } = require("child_process");
+
+  const absoluteAppPath = path.join(repoRoot, appPath);
+  const pkgJsonPath = path.join(absoluteAppPath, "package.json");
+
+  if (!fs.existsSync(pkgJsonPath)) {
+    return { success: true }; // No package.json, skip build check
+  }
+
+  try {
+    const pkg = JSON.parse(fs.readFileSync(pkgJsonPath, "utf8"));
+    // Only verify if there is an explicit build script
+    if (!pkg.scripts || !pkg.scripts.build) {
+      return { success: true };
+    }
+
+    console.log(
+      `[Ralph Loop] Running automatic build verification: npm run build inside ${absoluteAppPath}...`,
+    );
+    // Run npm run build with a 45s timeout to prevent hanging
+    execSync("npm run build", {
+      cwd: absoluteAppPath,
+      stdio: "pipe",
+      timeout: 45000,
+    });
+    return { success: true };
+  } catch (err: any) {
+    const stderr = err.stderr
+      ? err.stderr.toString()
+      : err.message || String(err);
+    console.warn(`[Ralph Loop] Build verification failed:`, stderr);
+    return {
+      success: false,
+      error: stderr.slice(-3000), // Cap the log length to avoid flooding the prompt context
+    };
+  }
+}
+
 export interface OutputLine {
   ts: string;
   type: "step" | "stdout" | "stderr" | "info" | "error" | "done";
@@ -354,6 +398,37 @@ Do NOT run git commit or git push — the platform handles committing after you
         continue;
       }
 
+      // ── Cloud Build Verification (Ralph Loop integration) ──
+      if (opts.repoRoot && ralphIteration < 3) {
+        await emit({
+          ts: now(),
+          type: "info",
+          text: "🔍 [Ralph Loop] Initiating automatic build verification...",
+        });
+
+        const verification = runBuildVerification(opts.repoRoot, opts.appPath);
+        if (!verification.success) {
+          ralphIteration++;
+          await emit({
+            ts: now(),
+            type: "error",
+            text: `❌ [Ralph Loop] Build verification failed (iteration ${ralphIteration}/3). Feeding compilation errors back to the model...`,
+          });
+
+          history.push({
+            role: "user",
+            content: `Your previous edits completed, but the project's build check failed with compilation errors. Please fix these errors immediately so the build compiles clean:\n\n\`\`\`text\n${verification.error}\n\`\`\``,
+          });
+          continue;
+        } else {
+          await emit({
+            ts: now(),
+            type: "info",
+            text: "🟢 [Ralph Loop] Build verification passed successfully! 0 errors.",
+          });
+        }
+      }
+
       // If fully complete, trigger auto-commit and finish
       if (opts.autoApprove) {
         await autoCommitAndDeploy(opts, task, emit);