diff --git a/notebook-rerun-determinism-guard/README.md b/notebook-rerun-determinism-guard/README.md
new file mode 100644
index 00000000..3b4ab8cd
--- /dev/null
+++ b/notebook-rerun-determinism-guard/README.md
@@ -0,0 +1,25 @@
+# Notebook rerun determinism guard
+
+This module checks whether hosted notebooks can receive a reproducibility badge after a rerun.
+
+It focuses on one part of Scientific/Engineering Data & Code Hosting: stable notebook outputs. It does not run containers, call external compute, or access live datasets.
+
+## What it checks
+
+- environment digest
+- pinned random seed
+- raw data digest
+- output digest parity
+- numeric drift tolerance
+- missing figures
+- slow reruns
+- provenance bundle presence
+
+## Run it
+
+```bash
+node notebook-rerun-determinism-guard/test.js
+node notebook-rerun-determinism-guard/demo.js
+```
+
+The demo writes JSON and Markdown artifacts to `artifacts/`.
diff --git a/notebook-rerun-determinism-guard/artifacts/demo.gif b/notebook-rerun-determinism-guard/artifacts/demo.gif
new file mode 100644
index 00000000..32f54b57
Binary files /dev/null and b/notebook-rerun-determinism-guard/artifacts/demo.gif differ
diff --git a/notebook-rerun-determinism-guard/artifacts/demo.mp4 b/notebook-rerun-determinism-guard/artifacts/demo.mp4
new file mode 100644
index 00000000..1190f106
Binary files /dev/null and b/notebook-rerun-determinism-guard/artifacts/demo.mp4 differ
diff --git a/notebook-rerun-determinism-guard/artifacts/notebook-rerun-report.md b/notebook-rerun-determinism-guard/artifacts/notebook-rerun-report.md
new file mode 100644
index 00000000..fa2ed45b
--- /dev/null
+++ b/notebook-rerun-determinism-guard/artifacts/notebook-rerun-report.md
@@ -0,0 +1,22 @@
+# Notebook rerun determinism report
+
+## NB-100: RNA velocity notebook
+Decision: PUBLISH_REPRODUCIBLE
+Next step: publish the rerun badge and output manifest
+
+## NB-210: Climate downscaling notebook
+Decision: REVIEW_BEFORE_RELEASE
+Next step: ask a reviewer to approve the reproducibility packet
+Warnings:
+- rerun is slower than expected
+- provenance bundle is missing
+
+## NB-404: Tumor segmentation notebook
+Decision: HOLD_RELEASE
+Next step: hold the notebook until the rerun packet matches the baseline
+Blockers:
+- missing environment digest
+- random seed is not pinned
+- output digest changed from baseline
+- numeric drift exceeds allowed tolerance
+- expected figures are missing
diff --git a/notebook-rerun-determinism-guard/artifacts/notebook-rerun-results.json b/notebook-rerun-determinism-guard/artifacts/notebook-rerun-results.json
new file mode 100644
index 00000000..267aac4b
--- /dev/null
+++ b/notebook-rerun-determinism-guard/artifacts/notebook-rerun-results.json
@@ -0,0 +1,35 @@
+[
+  {
+    "notebookId": "NB-100",
+    "title": "RNA velocity notebook",
+    "decision": "PUBLISH_REPRODUCIBLE",
+    "blockers": [],
+    "warnings": [],
+    "nextStep": "publish the rerun badge and output manifest"
+  },
+  {
+    "notebookId": "NB-210",
+    "title": "Climate downscaling notebook",
+    "decision": "REVIEW_BEFORE_RELEASE",
+    "blockers": [],
+    "warnings": [
+      "rerun is slower than expected",
+      "provenance bundle is missing"
+    ],
+    "nextStep": "ask a reviewer to approve the reproducibility packet"
+  },
+  {
+    "notebookId": "NB-404",
+    "title": "Tumor segmentation notebook",
+    "decision": "HOLD_RELEASE",
+    "blockers": [
+      "missing environment digest",
+      "random seed is not pinned",
+      "output digest changed from baseline",
+      "numeric drift exceeds allowed tolerance",
+      "expected figures are missing"
+    ],
+    "warnings": [],
+    "nextStep": "hold the notebook until the rerun packet matches the baseline"
+  }
+]
\ No newline at end of file
diff --git a/notebook-rerun-determinism-guard/demo.js b/notebook-rerun-determinism-guard/demo.js
new file mode 100644
index 00000000..1861f44c
--- /dev/null
+++ b/notebook-rerun-determinism-guard/demo.js
@@ -0,0 +1,13 @@
+const fs = require("fs");
+const path = require("path");
+const packets = require("./sample-data.json");
+const { evaluateNotebooks, renderMarkdownReport } = require("./index");
+
+const artifactsDir = path.join(__dirname, "artifacts");
+fs.mkdirSync(artifactsDir, { recursive: true });
+
+const results = evaluateNotebooks(packets);
+fs.writeFileSync(path.join(artifactsDir, "notebook-rerun-results.json"), JSON.stringify(results, null, 2));
+fs.writeFileSync(path.join(artifactsDir, "notebook-rerun-report.md"), renderMarkdownReport(results));
+
+console.log(renderMarkdownReport(results));
diff --git a/notebook-rerun-determinism-guard/index.js b/notebook-rerun-determinism-guard/index.js
new file mode 100644
index 00000000..4191e50e
--- /dev/null
+++ b/notebook-rerun-determinism-guard/index.js
@@ -0,0 +1,67 @@
+function evaluateNotebook(packet) {
+  const blockers = [];
+  const warnings = [];
+
+  if (!packet.environmentDigest) blockers.push("missing environment digest");
+  if (!packet.randomSeedPinned) blockers.push("random seed is not pinned");
+  if (!packet.rawDataDigest) blockers.push("missing raw data digest");
+  if (!packet.outputDigest) blockers.push("missing output digest");
+  if (packet.baselineOutputDigest && packet.outputDigest && packet.baselineOutputDigest !== packet.outputDigest) {
+    blockers.push("output digest changed from baseline");
+  }
+  if (packet.numericDrift > packet.allowedDrift) blockers.push("numeric drift exceeds allowed tolerance");
+  if (packet.missingFigures > 0) blockers.push("expected figures are missing");
+  if (packet.rerunMinutes > packet.maxRerunMinutes) warnings.push("rerun is slower than expected");
+  if (!packet.provenanceAttached) warnings.push("provenance bundle is missing");
+
+  let decision = "PUBLISH_REPRODUCIBLE";
+  if (blockers.length) {
+    decision = "HOLD_RELEASE";
+  } else if (warnings.length) {
+    decision = "REVIEW_BEFORE_RELEASE";
+  }
+
+  return {
+    notebookId: packet.id,
+    title: packet.title,
+    decision,
+    blockers,
+    warnings,
+    nextStep: nextStepFor(decision),
+  };
+}
+
+function nextStepFor(decision) {
+  if (decision === "PUBLISH_REPRODUCIBLE") return "publish the rerun badge and output manifest";
+  if (decision === "REVIEW_BEFORE_RELEASE") return "ask a reviewer to approve the reproducibility packet";
+  return "hold the notebook until the rerun packet matches the baseline";
+}
+
+function evaluateNotebooks(packets) {
+  return packets.map(evaluateNotebook);
+}
+
+function renderMarkdownReport(results) {
+  const lines = ["# Notebook rerun determinism report", ""];
+  for (const result of results) {
+    lines.push(`## ${result.notebookId}: ${result.title}`);
+    lines.push(`Decision: ${result.decision}`);
+    lines.push(`Next step: ${result.nextStep}`);
+    if (result.blockers.length) {
+      lines.push("Blockers:");
+      for (const blocker of result.blockers) lines.push(`- ${blocker}`);
+    }
+    if (result.warnings.length) {
+      lines.push("Warnings:");
+      for (const warning of result.warnings) lines.push(`- ${warning}`);
+    }
+    lines.push("");
+  }
+  return lines.join("\n");
+}
+
+module.exports = {
+  evaluateNotebook,
+  evaluateNotebooks,
+  renderMarkdownReport,
+};
diff --git a/notebook-rerun-determinism-guard/sample-data.json b/notebook-rerun-determinism-guard/sample-data.json
new file mode 100644
index 00000000..86068eb0
--- /dev/null
+++ b/notebook-rerun-determinism-guard/sample-data.json
@@ -0,0 +1,47 @@
+[
+  {
+    "id": "NB-100",
+    "title": "RNA velocity notebook",
+    "environmentDigest": "env-a12",
+    "randomSeedPinned": true,
+    "rawDataDigest": "raw-991",
+    "baselineOutputDigest": "out-441",
+    "outputDigest": "out-441",
+    "numericDrift": 0.002,
+    "allowedDrift": 0.01,
+    "missingFigures": 0,
+    "rerunMinutes": 12,
+    "maxRerunMinutes": 20,
+    "provenanceAttached": true
+  },
+  {
+    "id": "NB-210",
+    "title": "Climate downscaling notebook",
+    "environmentDigest": "env-b77",
+    "randomSeedPinned": true,
+    "rawDataDigest": "raw-103",
+    "baselineOutputDigest": "out-915",
+    "outputDigest": "out-915",
+    "numericDrift": 0.004,
+    "allowedDrift": 0.01,
+    "missingFigures": 0,
+    "rerunMinutes": 42,
+    "maxRerunMinutes": 30,
+    "provenanceAttached": false
+  },
+  {
+    "id": "NB-404",
+    "title": "Tumor segmentation notebook",
+    "environmentDigest": "",
+    "randomSeedPinned": false,
+    "rawDataDigest": "raw-700",
+    "baselineOutputDigest": "out-201",
+    "outputDigest": "out-999",
+    "numericDrift": 0.09,
+    "allowedDrift": 0.02,
+    "missingFigures": 2,
+    "rerunMinutes": 18,
+    "maxRerunMinutes": 25,
+    "provenanceAttached": true
+  }
+]
diff --git a/notebook-rerun-determinism-guard/test.js b/notebook-rerun-determinism-guard/test.js
new file mode 100644
index 00000000..adac2c7b
--- /dev/null
+++ b/notebook-rerun-determinism-guard/test.js
@@ -0,0 +1,15 @@
+const assert = require("assert");
+const packets = require("./sample-data.json");
+const { evaluateNotebooks } = require("./index");
+
+const results = evaluateNotebooks(packets);
+const byId = Object.fromEntries(results.map((result) => [result.notebookId, result]));
+
+assert.strictEqual(byId["NB-100"].decision, "PUBLISH_REPRODUCIBLE");
+assert.strictEqual(byId["NB-210"].decision, "REVIEW_BEFORE_RELEASE");
+assert.ok(byId["NB-210"].warnings.some((warning) => warning.includes("slower")));
+assert.strictEqual(byId["NB-404"].decision, "HOLD_RELEASE");
+assert.ok(byId["NB-404"].blockers.some((blocker) => blocker.includes("output digest")));
+assert.ok(byId["NB-404"].blockers.some((blocker) => blocker.includes("random seed")));
+
+console.log("notebook rerun determinism guard tests passed");