diff --git a/scripts/src/hwlab-node-web-observe-runner-source.ts b/scripts/src/hwlab-node-web-observe-runner-source.ts
index f0c1abda..00f287a5 100644
--- a/scripts/src/hwlab-node-web-observe-runner-source.ts
+++ b/scripts/src/hwlab-node-web-observe-runner-source.ts
@@ -73,6 +73,7 @@ let pageLoadSeq = 0;
 let controlPageEpoch = 0;
 let observerPageEpoch = 0;
 let currentPageProvenance = null;
+let heartbeatPulseTimer = null;
 const jsonlRotation = { stamp: compactFileTimestamp(startedAt), files: [] };
 
 try {
@@ -81,6 +82,7 @@ try {
   await rotateExistingJsonlArtifacts();
   await writeManifest({ status: "starting" });
   await writeHeartbeat({ status: "starting" });
+  heartbeatPulseTimer = startHeartbeatPulse();
   if (jsonlRotation.files.length > 0) await appendJsonl(files.control, eventRecord("jsonl-rotated", { stamp: jsonlRotation.stamp, archiveDir: path.relative(stateDir, dirs.archive), files: jsonlRotation.files, valuesRedacted: true }));
   const launcher = await import(pathToFileURL(path.resolve("scripts/src/browser-launcher.mjs")).href);
   const { chromium } = await launcher.importPlaywright();
@@ -126,6 +128,7 @@ try {
   await writeManifest({ status: "failed", error: errorSummary(error) }).catch(() => {});
   process.exitCode = 2;
 } finally {
+  if (heartbeatPulseTimer) clearInterval(heartbeatPulseTimer);
   if (browser) await browser.close().catch(() => {});
 }
 
@@ -221,6 +224,16 @@ async function writeHeartbeat(extra = {}) {
   await writeFile(files.heartbeat, JSON.stringify(heartbeat, null, 2) + "\n", { mode: 0o600 });
 }
 
+function startHeartbeatPulse() {
+  const timer = setInterval(() => {
+    if (stopping) return;
+    void writeHeartbeat({ status: terminalStatus, heartbeatPulse: true })
+      .catch((error) => appendJsonl(files.errors, eventRecord("heartbeat-pulse-error", { error: errorSummary(error) })));
+  }, 5000);
+  if (timer && typeof timer.unref === "function") timer.unref();
+  return timer;
+}
+
 function attachPassiveListeners(targetPage, pageRole = "control", targetPageId = pageId) {
   targetPage.on("request", (request) => {
     void appendJsonl(files.network, eventRecord("request", {
@@ -3197,19 +3210,24 @@ async function preflightSummary() {
 async function samplePage(reason, options = {}) {
   if (options?.refreshObserver !== false) await maybeRefreshObserverPage(reason);
   const groupSeq = sampleSeq + 1;
-  if (page && !page.isClosed()) await sampleOnePage(page, { reason, groupSeq, pageRole: "control", targetPageId: pageId, pageEpoch: controlPageEpoch });
+  if (page && !page.isClosed()) {
+    await sampleOnePage(page, { reason, groupSeq, pageRole: "control", targetPageId: pageId, pageEpoch: controlPageEpoch })
+      .catch((error) => appendJsonl(files.errors, eventRecord("control-sample-error", { pageRole: "control", pageId, pageEpoch: controlPageEpoch, error: errorSummary(error) })));
+  }
   if (observerPage && !observerPage.isClosed()) {
     await sampleOnePage(observerPage, { reason, groupSeq, pageRole: "observer", targetPageId: observerPageId, pageEpoch: observerPageEpoch }).catch((error) => appendJsonl(files.errors, eventRecord("observer-sample-error", { pageRole: "observer", pageId: observerPageId, pageEpoch: observerPageEpoch, error: errorSummary(error) })));
   }
   if (options?.screenshot !== false && screenshotIntervalMs > 0 && Date.now() - lastScreenshotAtMs >= screenshotIntervalMs) {
-    await captureScreenshot("checkpoint", "jpeg").catch((error) => appendJsonl(files.errors, eventRecord("screenshot-error", { pageRole: "control", pageId, error: errorSummary(error) })));
+    await withHardTimeout(captureScreenshot("checkpoint", "jpeg"), 15000, "captureScreenshot checkpoint exceeded 15s")
+      .catch((error) => appendJsonl(files.errors, eventRecord("screenshot-error", { pageRole: "control", pageId, error: errorSummary(error) })));
   }
   await writeHeartbeat({ status: terminalStatus });
 }
 
 async function sampleOnePage(targetPage, { reason, groupSeq, pageRole, targetPageId, pageEpoch }) {
   sampleSeq += 1;
-  const dom = await targetPage.evaluate((input) => {
+  const evaluateTimeoutMs = Math.max(3000, Math.min(8000, Number(sampleIntervalMs) || 5000));
+  const dom = await withHardTimeout(targetPage.evaluate((input) => {
     const trim = (value, limit = 500) => String(value || "").replace(/\s+/g, " ").trim().slice(0, limit);
     const visible = (element) => {
       if (!element) return false;
@@ -3788,7 +3806,7 @@ async function sampleOnePage(targetPage, { reason, groupSeq, pageRole, targetPag
       },
       performance: performance.getEntriesByType("resource").slice(-80).map(resourceTimingSample),
     };
-  }, { projectManagement }).catch((error) => ({ error: errorSummary(error), url: pageUrl(targetPage) }));
+  }, { projectManagement }), evaluateTimeoutMs, "sampleOnePage DOM evaluate exceeded " + evaluateTimeoutMs + "ms").catch((error) => ({ error: errorSummary(error), url: pageUrl(targetPage) }));
   const sample = {
     seq: sampleSeq,
     sampleGroupSeq: groupSeq,