diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8735e58..b6ab8e2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -47,5 +47,8 @@ jobs:
       - name: Test published adapters
         run: pnpm test:built
 
+      - name: Test built Worker in workerd
+        run: pnpm test:workerd
+
       - name: Test
         run: pnpm test
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 9ae1749..3c4d886 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -52,6 +52,9 @@ jobs:
       - name: Run tests
         run: pnpm test
 
+      - name: Test built Worker in workerd
+        run: pnpm test:workerd
+
       - name: Create Release Pull Request or Publish to npm
         uses: changesets/action@v1
         with:
diff --git a/package.json b/package.json
index 3feede4..5e2ecaf 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,7 @@
     "build:apps": "turbo run build",
     "test": "turbo run test",
     "test:built": "pnpm --filter @atmo-dev/contrail test:built",
+    "test:workerd": "pnpm --filter @atmo-dev/contrail test:workerd",
     "bench": "node --no-warnings --experimental-strip-types apps/benchmark/src/bench.ts",
     "typecheck": "turbo run typecheck",
     "dev": "turbo run dev",
diff --git a/packages/contrail/package.json b/packages/contrail/package.json
index a2fa459..9f5c0a1 100644
--- a/packages/contrail/package.json
+++ b/packages/contrail/package.json
@@ -77,6 +77,7 @@
     "typecheck": "tsc --noEmit",
     "test": "vitest run",
     "test:built": "node tests/built-sqlite.mjs && node tests/built-alluvium.mjs && node tests/built-lexicons.mjs && node tests/built-client.mjs && node tests/built-changes.mjs",
+    "test:workerd": "node tests/workerd-smoke.mjs",
     "test:watch": "vitest"
   },
   "dependencies": {
diff --git a/packages/contrail/tests/workerd-smoke.mjs b/packages/contrail/tests/workerd-smoke.mjs
new file mode 100644
index 0000000..0f87b4a
--- /dev/null
+++ b/packages/contrail/tests/workerd-smoke.mjs
@@ -0,0 +1,215 @@
+import { spawn } from "node:child_process";
+import { mkdtemp, rm } from "node:fs/promises";
+import { createServer } from "node:net";
+import { tmpdir } from "node:os";
+import { resolve } from "node:path";
+
+const PACKAGE_ROOT = resolve(import.meta.dirname, "..");
+const STATE_DIR = await mkdtemp(
+  resolve(tmpdir(), "contrail-workerd-runtime-smoke-"),
+);
+const MARKER = "[ingest] cycle summary ";
+const ANSI = /\x1b\[[0-?]*[ -/]*[@-~]/g;
+
+async function availablePort() {
+  const server = createServer();
+  await new Promise((resolveReady, reject) => {
+    server.once("error", reject);
+    server.listen(0, "127.0.0.1", resolveReady);
+  });
+  const address = server.address();
+  const port = typeof address === "object" && address ? address.port : null;
+  await new Promise((resolveClosed) => server.close(resolveClosed));
+  if (port === null) throw new Error("Could not allocate a local port");
+  return port;
+}
+
+const port = await availablePort();
+const inspectorPort = await availablePort();
+const origin = `http://127.0.0.1:${port}`;
+const wrangler = resolve(PACKAGE_ROOT, "node_modules/.bin/wrangler");
+let output = "";
+
+const child = spawn(
+  wrangler,
+  [
+    "dev",
+    "--config",
+    "tests/workerd/wrangler.jsonc",
+    "--port",
+    String(port),
+    "--inspector-port",
+    String(inspectorPort),
+    "--test-scheduled",
+    "--persist-to",
+    STATE_DIR,
+    "--log-level",
+    "log",
+  ],
+  {
+    cwd: PACKAGE_ROOT,
+    env: { ...process.env, CI: "true", NO_COLOR: "1" },
+    stdio: ["ignore", "pipe", "pipe"],
+  },
+);
+child.stdout.setEncoding("utf8");
+child.stderr.setEncoding("utf8");
+child.stdout.on("data", (chunk) => {
+  output += chunk;
+});
+child.stderr.on("data", (chunk) => {
+  output += chunk;
+});
+
+function summaries() {
+  const parsed = [];
+  for (const line of output.replace(ANSI, "").split("\n")) {
+    const marker = line.indexOf(MARKER);
+    if (marker === -1) continue;
+    try {
+      parsed.push(JSON.parse(line.slice(marker + MARKER.length)));
+    } catch {
+      // Ignore a line while Wrangler is still streaming it.
+    }
+  }
+  return parsed;
+}
+
+async function state() {
+  const response = await fetch(`${origin}/__contrail_workerd_smoke`, {
+    signal: AbortSignal.timeout(2_000),
+  });
+  if (!response.ok) {
+    throw new Error(`Smoke state endpoint returned ${response.status}`);
+  }
+  return response.json();
+}
+
+async function waitFor(read, predicate, label, timeoutMs = 30_000) {
+  const deadline = Date.now() + timeoutMs;
+  let lastError;
+  while (Date.now() < deadline) {
+    if (child.exitCode !== null) {
+      throw new Error(`Wrangler exited early with code ${child.exitCode}`);
+    }
+    try {
+      const value = await read();
+      if (predicate(value)) return value;
+    } catch (error) {
+      lastError = error;
+    }
+    await new Promise((resolveWait) => setTimeout(resolveWait, 250));
+  }
+  throw new Error(
+    `Timed out waiting for ${label}${lastError ? `: ${lastError}` : ""}`,
+  );
+}
+
+async function triggerScheduled() {
+  const response = await fetch(`${origin}/__scheduled`, {
+    signal: AbortSignal.timeout(15_000),
+  });
+  if (!response.ok) {
+    throw new Error(`Scheduled trigger returned ${response.status}`);
+  }
+}
+
+async function advanceCursor(predicate, label) {
+  for (let attempt = 1; attempt <= 3; attempt++) {
+    await triggerScheduled();
+    try {
+      return await waitFor(state, predicate, label, 20_000);
+    } catch (error) {
+      if (attempt === 3) throw error;
+    }
+  }
+  throw new Error(`Could not ${label}`);
+}
+
+function assert(condition, message) {
+  if (!condition) throw new Error(message);
+}
+
+async function stopWrangler() {
+  if (child.exitCode !== null) return;
+  child.kill("SIGTERM");
+  await Promise.race([
+    new Promise((resolveExit) => child.once("exit", resolveExit)),
+    new Promise((resolveTimeout) => setTimeout(resolveTimeout, 5_000)),
+  ]);
+  if (child.exitCode === null) child.kill("SIGKILL");
+}
+
+try {
+  const initial = await waitFor(state, () => true, "Wrangler startup");
+  assert(
+    initial.cpuUsage?.exposed === true && initial.cpuUsage?.throws === true,
+    `Expected workerd to expose a throwing process.cpuUsage stub, got ${JSON.stringify(initial.cpuUsage)}`,
+  );
+
+  const first = await advanceCursor(
+    (value) => value.cursorDomain === "seq",
+    "the timestamp bridge to commit a sequence cursor",
+  );
+  assert(
+    Number.isSafeInteger(first.cursor) && first.cursor >= 0,
+    `Invalid first sequence cursor: ${first.cursor}`,
+  );
+
+  const second = await advanceCursor(
+    (value) =>
+      value.cursorDomain === "seq" &&
+      Number.isSafeInteger(value.cursor) &&
+      value.cursor > first.cursor,
+    "an existing sequence cursor to pass preflight and advance",
+  );
+
+  await waitFor(
+    async () => summaries(),
+    (values) =>
+      values.some(
+        (summary) =>
+          summary.starting_cursor === first.cursor &&
+          summary.safe_ending_cursor === second.cursor,
+      ),
+    "the resumed sequence-cycle summary",
+    5_000,
+  );
+
+  const cycleSummaries = summaries();
+  const firstSummary = cycleSummaries.find(
+    (summary) => summary.safe_ending_cursor === first.cursor,
+  );
+  const secondSummary = cycleSummaries.find(
+    (summary) =>
+      summary.starting_cursor === first.cursor &&
+      summary.safe_ending_cursor === second.cursor,
+  );
+  assert(firstSummary, "Missing timestamp-bridge cycle summary");
+  assert(secondSummary, "Missing resumed sequence-cycle summary");
+  for (const [label, summary] of [
+    ["bridge", firstSummary],
+    ["resumed seq", secondSummary],
+  ]) {
+    assert(
+      summary.connection_errors === 0,
+      `${label} cycle reported connection_errors=${summary.connection_errors}`,
+    );
+    assert(
+      summary.cpu_ms === null,
+      `${label} cycle did not degrade throwing CPU telemetry to null`,
+    );
+  }
+
+  console.log(
+    `workerd smoke passed: ${first.cursor} -> ${second.cursor}; ` +
+      "host fetch preflight succeeded and cpu_ms=null",
+  );
+} catch (error) {
+  console.error(error);
+  console.error("\n--- Wrangler output ---\n" + output.slice(-30_000));
+  process.exitCode = 1;
+} finally {
+  await stopWrangler();
+  await rm(STATE_DIR, { recursive: true, force: true });
+}
diff --git a/packages/contrail/tests/workerd/worker.mjs b/packages/contrail/tests/workerd/worker.mjs
new file mode 100644
index 0000000..07b8fc8
--- /dev/null
+++ b/packages/contrail/tests/workerd/worker.mjs
@@ -0,0 +1,67 @@
+import { createWorker } from "../../dist/worker/index.js";
+
+const JETSTREAM_V2_SEQ_THRESHOLD = 1_000_000_000_000_000;
+
+const config = {
+  namespace: "com.example",
+  profiles: [],
+  constellation: false,
+  jetstreams: ["https://jetstream.us-east.bsky.network"],
+  orderedSource: {
+    source: "jetstream",
+    epoch: "contrail-workerd-runtime-smoke-v1",
+  },
+  collections: {
+    post: { collection: "app.bsky.feed.post" },
+  },
+  logger: console,
+};
+
+const worker = createWorker(config, {
+  scheduledIngest: {
+    maxDrainMs: 8_000,
+    maxCandidates: 1,
+    maxIdentityUpdates: 1,
+    maxSerializedBytes: 1024 * 1024,
+  },
+  backfillRetries: false,
+});
+
+function cpuUsageCapability() {
+  const runtimeProcess = globalThis.process;
+  const exposed = typeof runtimeProcess?.cpuUsage === "function";
+  if (!exposed) return { exposed, throws: false };
+  try {
+    runtimeProcess.cpuUsage();
+    return { exposed, throws: false };
+  } catch (error) {
+    return { exposed, throws: true, error: String(error) };
+  }
+}
+
+export default {
+  async fetch(request, env, ctx) {
+    const url = new URL(request.url);
+    if (url.pathname === "/__contrail_workerd_smoke") {
+      // Exercise the built Worker's lazy initialization before inspecting its
+      // durable cursor directly through the real local D1 binding.
+      await worker.fetch(new Request(new URL("/health", url)), env, ctx);
+      const row = await env.DB.prepare(
+        "SELECT time_us FROM cursor WHERE id = 1",
+      ).first();
+      const cursor = row?.time_us ?? null;
+      return Response.json({
+        cursor,
+        cursorDomain:
+          cursor === null
+            ? null
+            : cursor < JETSTREAM_V2_SEQ_THRESHOLD
+              ? "seq"
+              : "timestamp",
+        cpuUsage: cpuUsageCapability(),
+      });
+    }
+    return worker.fetch(request, env, ctx);
+  },
+  scheduled: worker.scheduled,
+};
diff --git a/packages/contrail/tests/workerd/wrangler.jsonc b/packages/contrail/tests/workerd/wrangler.jsonc
new file mode 100644
index 0000000..9d2e896
--- /dev/null
+++ b/packages/contrail/tests/workerd/wrangler.jsonc
@@ -0,0 +1,13 @@
+{
+  "name": "contrail-workerd-runtime-smoke",
+  "main": "worker.mjs",
+  "compatibility_date": "2026-08-06",
+  "compatibility_flags": ["nodejs_compat"],
+  "d1_databases": [
+    {
+      "binding": "DB",
+      "database_name": "contrail-workerd-runtime-smoke",
+      "database_id": "00000000-0000-0000-0000-000000000001"
+    }
+  ]
+}