fix(il2cpp): reject duplicate method tokens per image

Reject duplicate MethodDef row identities within one owning image before publishing native addresses or Ghidra seeds, while retaining cross-image reuse and folded code addresses.

Fixes #6610

src/il2cpp/Il2cppBinaryFile.ts

@@ -90,6 +90,25 @@ export function* linkIl2cppBinarySteps(
         methodImage[type.method_start + method] = index;
       }
     }
+  const methodByImageAndRow = metadata.images.map(
+    () => new Map<number, number>(),
+  );
+  for (let index = 0; index < methodImage.length; index++) {
+    if (index % LINK_BATCH === 0) yield;
+    const owner = methodImage[index]!;
+    if (owner === -1) continue;
+    const token = facts.methodTokens[index]!;
+    const row = token & 0xffffff;
+    if (token >>> 24 !== 0x06 || row === 0) continue;
+    const methodsByRow = methodByImageAndRow[owner]!;
+    const earlier = methodsByRow.get(row);
+    if (earlier !== undefined)
+      throw new Il2cppBinaryFormatFailure(
+        "invalid-method-token",
+        `methods ${earlier} and ${index} in image ${metadata.images[owner]!.name} share MethodDef token 0x${token.toString(16)}`,
+      );
+    methodsByRow.set(row, index);
+  }
   yield;
   const methodAddress = (index: number): Il2cppMethodCode => {
     const owner = methodImage[index]!;