diff --git a/actions/setup/js/trace_graders.cjs b/actions/setup/js/trace_graders.cjs
index 4e9c0462249..0a2b64f3242 100644
--- a/actions/setup/js/trace_graders.cjs
+++ b/actions/setup/js/trace_graders.cjs
@@ -460,10 +460,40 @@ function evaluateThreshold(value, direction, threshold) {
 function sanitizeSummaryText(value) {
   return String(value ?? "")
     .replace(/\r?\n/g, " ")
+    .replace(/\\/g, "\\\\")
+    .replace(/\|/g, "\\|")
     .replace(/[<>&]/g, ch => (ch === "<" ? "&lt;" : ch === ">" ? "&gt;" : "&amp;"))
     .trim();
 }
 
+/**
+ * @param {GraderResult} result
+ * @returns {result is GraderResult & {value: number}}
+ */
+function hasComputedValue(result) {
+  return typeof result.value === "number";
+}
+
+/**
+ * Build the Graders section body for the GitHub Actions step summary.
+ * @param {GraderResult[]} results
+ * @returns {string}
+ */
+function buildGradersSummaryBody(results) {
+  const computedResults = results.filter(hasComputedValue);
+  if (computedResults.length === 0) {
+    return "\n\nNo grader values available.\n\n";
+  }
+
+  const statusLabels = { pass: "Pass", fail: "Fail", error: "Error", unavailable: "Unavailable" };
+  const rows = computedResults.map(result => {
+    const value = String(Number(result.value.toFixed(4)));
+    return `| ${statusLabels[result.status] || "Unknown"} | ${sanitizeSummaryText(result.name)} | ${sanitizeSummaryText(result.source)} | ${value} | ${sanitizeSummaryText(result.unit || "—")} |`;
+  });
+
+  return ["", "", "| Status | Grader | Source | Value | Unit |", "| --- | --- | --- | --- | --- |", ...rows, "", ""].join("\n");
+}
+
 /**
  * Normalize a grader result from either built-in number or custom object return.
  * @param {string} id
@@ -806,25 +836,7 @@ async function main(manifestB64, execSpecB64) {
   }
 
   // Step summary
-  core.summary.addHeading("Graders", 3);
-  const tableResults = results.filter(r => r.status !== "unavailable");
-  if (tableResults.length > 0) {
-    const rows = tableResults.map(r => {
-      const statusIcon = r.status === "pass" ? "✅" : r.status === "fail" ? "❌" : "⚠️";
-      const val = r.value !== null ? String(Number(r.value.toFixed(4))) : "—";
-      return [statusIcon, sanitizeSummaryText(r.name), r.source, val, sanitizeSummaryText(r.unit || "—")];
-    });
-    core.summary.addTable([
-      [
-        { data: "", header: true },
-        { data: "Grader", header: true },
-        { data: "Source", header: true },
-        { data: "Value", header: true },
-        { data: "Unit", header: true },
-      ],
-      ...rows,
-    ]);
-  }
+  core.summary.addDetails("Graders", buildGradersSummaryBody(results));
   const errResults = results.filter(r => r.error);
   if (errResults.length > 0) {
     const errLines = errResults.map(r => `- **${sanitizeSummaryText(r.id)}**: runtime error (see step logs)`).join("\n");
@@ -850,6 +862,7 @@ module.exports = {
   runCustomGrader,
   runOperationalValueGrader,
   normalizeResult,
+  buildGradersSummaryBody,
   evaluateThreshold,
   BUILTIN_GRADERS,
   BUILTIN_META,
diff --git a/actions/setup/js/trace_graders.test.cjs b/actions/setup/js/trace_graders.test.cjs
index 7b4aa60e201..3c837464f11 100644
--- a/actions/setup/js/trace_graders.test.cjs
+++ b/actions/setup/js/trace_graders.test.cjs
@@ -20,6 +20,7 @@ const {
   runBuiltinGrader,
   runCustomGrader,
   normalizeResult,
+  buildGradersSummaryBody,
   evaluateThreshold,
   BUILTIN_GRADERS,
   BUILTIN_META,
@@ -68,6 +69,42 @@ function makeTrace(overrides = {}) {
 }
 
 describe("trace_graders", () => {
+  describe("buildGradersSummaryBody", () => {
+    it("renders all computed grader values without emojis", () => {
+      const summary = buildGradersSummaryBody([
+        { id: "tool-success-rate", name: "Tool success rate", value: 0.98765, unit: "ratio", status: "pass", source: "builtin" },
+        { id: "custom", name: "Custom", value: 2, unit: "count", status: "fail", source: "inline" },
+        { id: "unavailable", name: "Unavailable", value: null, unit: "", status: "unavailable", source: "builtin" },
+      ]);
+
+      expect(summary).toContain("| Pass | Tool success rate | builtin | 0.9877 | ratio |");
+      expect(summary).toContain("| Fail | Custom | inline | 2 | count |");
+      expect(summary).not.toContain("Unavailable");
+      expect(summary).not.toMatch(/[\u{1F300}-\u{1FAFF}]/u);
+    });
+
+    it("escapes untrusted table cells", () => {
+      const summary = buildGradersSummaryBody([{ id: "custom", name: "Custom | <grader>", value: 1, unit: "unit|&", status: "pass", source: "inline|source" }]);
+
+      expect(summary).toContain("Custom \\| &lt;grader&gt;");
+      expect(summary).toContain("inline\\|source");
+      expect(summary).toContain("unit\\|&amp;");
+    });
+
+    it("escapes backslashes before pipes", () => {
+      const summary = buildGradersSummaryBody([{ id: "custom", name: "A\\|B", value: 1, unit: "count", status: "pass", source: "inline" }]);
+
+      expect(summary).toContain("| Pass | A\\\\\\|B | inline | 1 | count |");
+    });
+
+    it("surrounds the table with blank lines for details rendering", () => {
+      const summary = buildGradersSummaryBody([{ id: "custom", name: "Custom", value: 1, unit: "count", status: "pass", source: "inline" }]);
+
+      expect(summary.startsWith("\n\n")).toBe(true);
+      expect(summary.endsWith("\n\n")).toBe(true);
+    });
+  });
+
   describe("archiveOperationalValueEvaluator", () => {
     it("writes only evaluator bytes matching the frozen digest", () => {
       const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "operational-value-evaluator-archive-"));