diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3220481..6aba14c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -118,7 +118,7 @@ jobs:
   test-smoke:
     name: Smoke Tests
     runs-on: ubuntu-latest
-    timeout-minutes: 15
+    timeout-minutes: 30
     services:
       postgres:
         image: postgres:17
diff --git a/packages/core/tests/integration/smoke/site-matrix-smoke.test.ts b/packages/core/tests/integration/smoke/site-matrix-smoke.test.ts
index 2f2bf93..6d0ec10 100644
--- a/packages/core/tests/integration/smoke/site-matrix-smoke.test.ts
+++ b/packages/core/tests/integration/smoke/site-matrix-smoke.test.ts
@@ -180,7 +180,48 @@ async function fetchWithRetry(url: string, retries = 10, delayMs = 1500): Promis
 	throw lastError instanceof Error ? lastError : new Error(`Request failed for ${url}`);
 }
 
-describe.sequential("Site smoke matrix", () => {
+// ---------------------------------------------------------------------------
+// Build verification — runs `astro build` for every site to catch adapter
+// and bundling errors that dev mode doesn't surface.
+// ---------------------------------------------------------------------------
+
+describe.sequential("Site build verification", () => {
+	const BUILD_TIMEOUT = 120_000;
+
+	for (const site of SITE_MATRIX) {
+		if (site.mode === "typecheck") continue;
+
+		it(`${site.name} builds successfully`, { timeout: BUILD_TIMEOUT + 30_000 }, async () => {
+			await ensureBuilt();
+
+			try {
+				await execAsync("pnpm", ["exec", "astro", "build"], {
+					cwd: site.dir,
+					timeout: BUILD_TIMEOUT,
+					env: {
+						...process.env,
+						CI: "true",
+					},
+				});
+			} catch (error) {
+				const stderr =
+					error instanceof Error && "stderr" in error ? (error as { stderr: string }).stderr : "";
+				const stdout =
+					error instanceof Error && "stdout" in error ? (error as { stdout: string }).stdout : "";
+				throw new Error(`${site.name} build failed:\n\n${stderr || stdout}`.slice(0, 5000), {
+					cause: error,
+				});
+			}
+		});
+	}
+});
+
+// ---------------------------------------------------------------------------
+// Runtime verification — boots each site with `astro dev` and checks that
+// admin + frontend respond.
+// ---------------------------------------------------------------------------
+
+describe.sequential("Site runtime verification", () => {
 	for (const site of SITE_MATRIX) {
 		if (site.mode === "typecheck") {
 			it(`${site.name} typechecks`, { timeout: 120_000 }, async () => {