diff --git a/actions/setup/js/messages_header.cjs b/actions/setup/js/messages_header.cjs
index 87fdcea0509..6a13fe17306 100644
--- a/actions/setup/js/messages_header.cjs
+++ b/actions/setup/js/messages_header.cjs
@@ -20,7 +20,14 @@ const { getMessages, getPromptPath, renderTemplate, renderTemplateFromFile, toSn
 const DEFAULT_DISCLOSURE_HEADER_TEMPLATE = "safe_outputs_disclosure_header.md";
 const DISCLOSURE_HEADER_DEFAULT_SENTINEL = "true";
 
-const DEFAULT_DISCLOSURE_HEADER = renderTemplateFromFile(getPromptPath(DEFAULT_DISCLOSURE_HEADER_TEMPLATE), {}).trimEnd();
+let defaultDisclosureHeader;
+
+function getDefaultDisclosureHeader() {
+  if (defaultDisclosureHeader === undefined) {
+    defaultDisclosureHeader = renderTemplateFromFile(getPromptPath(DEFAULT_DISCLOSURE_HEADER_TEMPLATE), {}).trimEnd();
+  }
+  return defaultDisclosureHeader;
+}
 
 /**
  * Get the body header text, using the custom template if configured.
@@ -55,7 +62,7 @@ function getDisclosureHeader(ctx) {
 
   let template = "";
   if (disclosureHeader === true || disclosureHeader === DISCLOSURE_HEADER_DEFAULT_SENTINEL) {
-    template = DEFAULT_DISCLOSURE_HEADER;
+    template = getDefaultDisclosureHeader();
   } else if (typeof disclosureHeader === "string") {
     template = disclosureHeader;
   } else {
@@ -69,6 +76,8 @@ function getDisclosureHeader(ctx) {
 module.exports = {
   getBodyHeader,
   getDisclosureHeader,
-  DEFAULT_DISCLOSURE_HEADER,
+  get DEFAULT_DISCLOSURE_HEADER() {
+    return getDefaultDisclosureHeader();
+  },
   DISCLOSURE_HEADER_DEFAULT_SENTINEL,
 };
diff --git a/actions/setup/js/messages_header.test.cjs b/actions/setup/js/messages_header.test.cjs
index 0a1b8ca56d2..148f3230684 100644
--- a/actions/setup/js/messages_header.test.cjs
+++ b/actions/setup/js/messages_header.test.cjs
@@ -24,6 +24,39 @@ let DISCLOSURE_HEADER_DEFAULT_SENTINEL;
 const WORKFLOW = "My Workflow";
 const RUN_URL = "https://github.com/owner/repo/actions/runs/99";
 
+describe("messages_header module loading", () => {
+  it("does not require prompt templates until default disclosure text is rendered", () => {
+    const originalPromptsDir = process.env.GH_AW_PROMPTS_DIR;
+    const originalRunnerTemp = process.env.RUNNER_TEMP;
+    const modulePath = require.resolve("./messages_header.cjs");
+
+    try {
+      delete process.env.GH_AW_PROMPTS_DIR;
+      delete process.env.RUNNER_TEMP;
+      delete require.cache[modulePath];
+
+      const headerModule = require("./messages_header.cjs");
+      expect(headerModule.getBodyHeader({ workflowName: WORKFLOW, runUrl: RUN_URL })).toBe("");
+
+      process.env.GH_AW_SAFE_OUTPUT_MESSAGES = JSON.stringify({ disclosureHeader: true });
+      expect(() => headerModule.getDisclosureHeader({ workflowName: WORKFLOW, runUrl: RUN_URL })).toThrow(/Cannot resolve prompt path/);
+    } finally {
+      delete process.env.GH_AW_SAFE_OUTPUT_MESSAGES;
+      if (originalPromptsDir === undefined) {
+        delete process.env.GH_AW_PROMPTS_DIR;
+      } else {
+        process.env.GH_AW_PROMPTS_DIR = originalPromptsDir;
+      }
+      if (originalRunnerTemp === undefined) {
+        delete process.env.RUNNER_TEMP;
+      } else {
+        process.env.RUNNER_TEMP = originalRunnerTemp;
+      }
+      delete require.cache[modulePath];
+    }
+  });
+});
+
 describe("messages_header", () => {
   beforeAll(() => {
     originalPromptsDir = process.env.GH_AW_PROMPTS_DIR;