diff --git a/web/src/app/pattern-lab/HardwareModal.test.tsx b/web/src/app/pattern-lab/HardwareModal.test.tsx
index 15e5a536a..87f2d192d 100644
--- a/web/src/app/pattern-lab/HardwareModal.test.tsx
+++ b/web/src/app/pattern-lab/HardwareModal.test.tsx
@@ -155,6 +155,70 @@ describe("HardwareModal", () => {
     }
   });
 
+  // A chat answer copied whole carries the model's words and the ``` fence
+  // around the code. The box used to pass it as a header, because the check
+  // found #pragma once on any line, and the words went into the .h whole.
+  it("keeps only the header when a whole chat answer is pasted", async () => {
+    const header = [
+      "// SPDX-License-Identifier: CC-BY-SA-4.0",
+      "// Pattern: Wave",
+      "#pragma once",
+      "namespace LabWave {",
+      '  const char* NAME = "Wave";',
+      "  void draw() {}",
+      "} // namespace LabWave",
+    ].join("\n");
+    const reply = `Here is the converted header:\n\n\`\`\`cpp\n${header}\n\`\`\`\n\nLet me know if you want the colours warmer.`;
+    const writeText = vi.fn<(text: string) => Promise<void>>(() => Promise.resolve());
+    Object.defineProperty(navigator, "clipboard", { configurable: true, value: { writeText } });
+    try {
+      render(<Lab />);
+      fireEvent.change(screen.getByPlaceholderText(/Paste the \.h the model gives you/), {
+        target: { value: reply },
+      });
+      expect(screen.getByText(/Looks like a header ✓/)).toHaveTextContent("The words around it stay out of the .h.");
+
+      fireEvent.click(screen.getByText("Copy .h"));
+      expect(await screen.findByText("Copied ✓")).toBeTruthy();
+      const name = useLabStore.getState().layers[0].name;
+      expect(writeText).toHaveBeenCalledWith(header.replace('"Wave"', `"${name}"`));
+    } finally {
+      delete (navigator as { clipboard?: unknown }).clipboard;
+    }
+  });
+
+  it("finds no header in an answer whose #pragma once is in a sentence", () => {
+    render(<Lab />);
+    fireEvent.change(screen.getByPlaceholderText(/Paste the \.h the model gives you/), {
+      target: { value: "Sure. The header starts with #pragma once and ends with the namespace." },
+    });
+    expect(screen.getByText("A Patternflow header starts with #pragma once")).toBeTruthy();
+    expect(screen.getByText("Copy .h")).toBeDisabled();
+    expect(screen.getByText("Next →")).toBeDisabled();
+  });
+
+  // Copy .h used to be the one button open on an empty box. It put nothing
+  // on the clipboard and said Copied ✓.
+  it("keeps Copy .h shut until a header is pasted", () => {
+    const writeText = vi.fn<(text: string) => Promise<void>>(() => Promise.resolve());
+    Object.defineProperty(navigator, "clipboard", { configurable: true, value: { writeText } });
+    try {
+      render(<Lab />);
+      expect(screen.getByText("Copy .h")).toBeDisabled();
+      fireEvent.click(screen.getByText("Copy .h"));
+      expect(writeText).not.toHaveBeenCalled();
+      expect(screen.queryByText("Copied ✓")).toBeNull();
+
+      fireEvent.change(screen.getByPlaceholderText(/Paste the \.h the model gives you/), {
+        target: { value: HEADER },
+      });
+      expect(screen.getByText("Looks like a header ✓")).toBeTruthy();
+      expect(screen.getByText("Copy .h")).toBeEnabled();
+    } finally {
+      delete (navigator as { clipboard?: unknown }).clipboard;
+    }
+  });
+
   // Text and pixel layers are in the scaffold as pixels, so with no code
   // layer the header is whole. The window used to count "0 layers to
   // translate — 0 done" and send the person to a model anyway.
diff --git a/web/src/app/pattern-lab/HardwareModal.tsx b/web/src/app/pattern-lab/HardwareModal.tsx
index 9f0542ece..bb080ff5b 100644
--- a/web/src/app/pattern-lab/HardwareModal.tsx
+++ b/web/src/app/pattern-lab/HardwareModal.tsx
@@ -4,7 +4,13 @@ import { useEffect, useMemo, useState, type MouseEvent } from "react";
 import { PublishModal, SendModuleModal, buildsConfigured, communityConfigured } from "./community";
 import { useDialog } from "@/lib/hooks/useDialog";
 import { useResettingState } from "@/lib/hooks/useResettingState";
-import { assembleH, buildHExport, cleanPastedUnit, enforcePatternName } from "@/lib/lab/hExport";
+import {
+  assembleH,
+  buildHExport,
+  cleanPastedHeader,
+  cleanPastedUnit,
+  enforcePatternName,
+} from "@/lib/lab/hExport";
 import { buildCppPrompt } from "@/lib/lab/cppPrompt";
 import { currentPerformanceJson } from "@/lib/lab/director/publish";
 import { needsFlatten } from "@/lib/lab/flatten";
@@ -85,14 +91,21 @@ export default function HardwareModal({
     });
   }, [layers, activeLayerId, codeLayers, matrix, knobs, ranges, knobLabels, name]);
 
+  // A chat answer pasted whole used to go into the .h with the model's words
+  // and the ``` fence, and the header test below passed it.
+  const singleHeader = useMemo(() => cleanPastedHeader(single), [single]);
+  const wordsLeftOut = singleHeader !== null && singleHeader !== single.trim();
+
   // Single path: the model writes NAME itself, so stamp the lab's name back
   // on (the scaffold path already carries it — buildHExport bakes it in).
   const assembled = useMemo(
     () =>
       stacked
         ? assembleH(exportData.scaffold, pastes)
-        : enforcePatternName(single.trim(), name),
-    [stacked, exportData.scaffold, pastes, single, name],
+        : singleHeader === null
+          ? ""
+          : enforcePatternName(singleHeader, name),
+    [stacked, exportData.scaffold, pastes, singleHeader, name],
   );
 
   // Text and pixel layers go into the scaffold as the pixels they show, so
@@ -287,13 +300,18 @@ export default function HardwareModal({
                       {headerLooksReal
                         ? "Looks like a header ✓"
                         : "A Patternflow header starts with #pragma once"}
+                      {wordsLeftOut ? " The words around it stay out of the .h." : null}
                     </p>
                   )}
                 </>
               )}
 
               <div className={styles.variantActions} style={{ marginTop: 10, flexWrap: "wrap" }}>
-                <button type="button" onClick={() => void copyText("h", assembled)}>
+                <button
+                  type="button"
+                  onClick={() => void copyText("h", assembled)}
+                  disabled={!headerLooksReal}
+                >
                   {copyLabel("h", "Copy .h")}
                 </button>
                 <button type="button" onClick={downloadH} disabled={!headerLooksReal}>
diff --git a/web/src/lib/lab/hExport.ts b/web/src/lib/lab/hExport.ts
index f5d85ec9a..a962b02d8 100644
--- a/web/src/lib/lab/hExport.ts
+++ b/web/src/lib/lab/hExport.ts
@@ -725,6 +725,26 @@ export function cleanPastedUnit(pasted: string, index: number): string | null {
   return text;
 }
 
+/**
+ * Cut a pasted one-layer answer down to the header. A chat answer copied whole
+ * brings the model's words and the ``` fence along. The header starts at the
+ * line #pragma once, or at the comment lines just above it (presets open with
+ * their SPDX line), and ends where a fence closes. null when no line starts
+ * with #pragma once.
+ */
+export function cleanPastedHeader(pasted: string): string | null {
+  const lines = pasted.split("\n");
+  const pragma = lines.findIndex((line) => /^\s*#pragma\s+once\b/.test(line));
+  if (pragma < 0) return null;
+  let start = pragma;
+  while (start > 0 && /^\s*(\/\/|\/\*|\*|$)/.test(lines[start - 1])) start -= 1;
+  const fence = lines.findIndex((line, i) => i > pragma && /^\s*```/.test(line));
+  return lines
+    .slice(start, fence < 0 ? lines.length : fence)
+    .join("\n")
+    .trim();
+}
+
 /** Swap pasted layer units into their marked slots. Missing units keep stubs. */
 export function assembleH(scaffold: string, units: Record<number, string>): string {
   let out = scaffold;