diff --git a/actions/setup/js/awf_reflect_summary.cjs b/actions/setup/js/awf_reflect_summary.cjs
index 37af29e18a9..8277dfbd6d1 100644
--- a/actions/setup/js/awf_reflect_summary.cjs
+++ b/actions/setup/js/awf_reflect_summary.cjs
@@ -1,6 +1,8 @@
 // @ts-check
 /// <reference types="@actions/github-script" />
 
+require("./shim.cjs");
+
 const fs = require("fs");
 
 const AWF_CONFIG_PATH = "/tmp/gh-aw/awf-config.json";
@@ -260,6 +262,8 @@ async function main() {
   }
 
   const markdown = buildReflectSummary(reflectData, { awfConfigData, runtimeModelsData });
+  // shim.cjs ensures core.summary.addRaw()/write() are available in environments
+  // without native GitHub Actions step-summary support.
   await core.summary.addRaw(markdown).write();
   core.info("AWF reflect summary written to step summary");
 }
diff --git a/actions/setup/js/awf_reflect_summary.test.cjs b/actions/setup/js/awf_reflect_summary.test.cjs
index 4eaf9ce4e8a..6437ac675bd 100644
--- a/actions/setup/js/awf_reflect_summary.test.cjs
+++ b/actions/setup/js/awf_reflect_summary.test.cjs
@@ -1,5 +1,8 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import fs from "fs";
+import { createRequire } from "module";
+
+const require = createRequire(import.meta.url);
 
 const mockCore = {
   info: vi.fn(),
@@ -380,5 +383,32 @@ describe("awf_reflect_summary.cjs", () => {
       expect(mockCore.summary.write).toHaveBeenCalledTimes(1);
       expect(mockCore.info).toHaveBeenCalledWith(expect.stringContaining("AWF reflect summary written"));
     });
+
+    it("uses shimmed summary methods when step summary API is missing", async () => {
+      const originalSummary = global.core.summary;
+      try {
+        global.core.summary = undefined;
+        const shimPath = require.resolve("./shim.cjs");
+        delete require.cache[shimPath];
+        require("./shim.cjs");
+        const addRawSpy = vi.spyOn(global.core.summary, "addRaw");
+        const writeSpy = vi.spyOn(global.core.summary, "write");
+        fs.writeFileSync(REFLECT_PATH, JSON.stringify(SAMPLE_REFLECT), "utf8");
+
+        await module.main();
+
+        expect(addRawSpy).toHaveBeenCalledTimes(1);
+        expect(writeSpy).toHaveBeenCalledTimes(1);
+        const summary = addRawSpy.mock.calls[0][0];
+        expect(summary).toContain("AWF API proxy");
+        expect(summary).toContain("openai");
+        expect(mockCore.info).toHaveBeenCalledWith(expect.stringContaining("AWF reflect summary written"));
+      } finally {
+        global.core.summary = originalSummary;
+        const shimPath = require.resolve("./shim.cjs");
+        delete require.cache[shimPath];
+        require("./shim.cjs");
+      }
+    });
   });
 });
diff --git a/actions/setup/js/pick_experiment.cjs b/actions/setup/js/pick_experiment.cjs
index 7fd9c61fe46..858c70f661b 100644
--- a/actions/setup/js/pick_experiment.cjs
+++ b/actions/setup/js/pick_experiment.cjs
@@ -234,7 +234,7 @@ async function writeSummary(assignments, configs, state, core) {
     lines.push(`| \`${name}\` | **${selected}** | ${thisCount} / ${totalCount} |`);
 
     const cfg = configs[name] || {};
-    const minSamples = Number.isInteger(cfg.min_samples) && cfg.min_samples > 0 ? cfg.min_samples : null;
+    const minSamples = typeof cfg.min_samples === "number" && Number.isInteger(cfg.min_samples) && cfg.min_samples > 0 ? cfg.min_samples : null;
     const analysisType = cfg.analysis_type || "n/a";
     const tags = Array.isArray(cfg.tags) ? cfg.tags.filter(t => typeof t === "string" && t.length > 0) : [];
     const notifyTargets = [];
diff --git a/actions/setup/js/shim.cjs b/actions/setup/js/shim.cjs
index c3f628f0013..f051446bed6 100644
--- a/actions/setup/js/shim.cjs
+++ b/actions/setup/js/shim.cjs
@@ -33,6 +33,16 @@ if (!global.core) {
   };
 }
 
+const coreSummary = global.core.summary && typeof global.core.summary === "object" ? global.core.summary : (global.core.summary = {});
+
+if (typeof coreSummary.addRaw !== "function") {
+  coreSummary.addRaw = () => coreSummary;
+}
+
+if (typeof coreSummary.write !== "function") {
+  coreSummary.write = async () => {};
+}
+
 if (!global.context) {
   // Build a context object from GitHub Actions environment variables,
   // mirroring the shape of @actions/github's Context class.