diff --git a/server-tools/lake-lamp-authz/architecture-provision-broker.js b/server-tools/lake-lamp-authz/architecture-provision-broker.js
index 660d93a..fae77f0 100644
--- a/server-tools/lake-lamp-authz/architecture-provision-broker.js
+++ b/server-tools/lake-lamp-authz/architecture-provision-broker.js
@@ -259,8 +259,14 @@ function backupFile(source, backup, records) {
   const stat = fs.lstatSync(source);
   if (!stat.isFile() || stat.isSymbolicLink()) throw new Error("backup_source_not_regular_file");
   fs.mkdirSync(path.dirname(backup), { recursive: true, mode: 0o700 });
-  fs.copyFileSync(source, backup, fs.constants.COPYFILE_EXCL);
-  fs.chmodSync(backup, stat.mode & 0o777);
+  if (fs.existsSync(backup)) {
+    const backupStat = fs.lstatSync(backup);
+    if (!backupStat.isFile() || backupStat.isSymbolicLink()) throw new Error("backup_conflict");
+    if (!fs.readFileSync(source).equals(fs.readFileSync(backup))) throw new Error("backup_conflict");
+  } else {
+    fs.copyFileSync(source, backup, fs.constants.COPYFILE_EXCL);
+    fs.chmodSync(backup, stat.mode & 0o777);
+  }
   records.push({ source, backup, existed: true, mode: stat.mode & 0o777 });
 }
 
diff --git a/server-tools/lake-lamp-authz/architecture-provision-broker.test.js b/server-tools/lake-lamp-authz/architecture-provision-broker.test.js
index 0ecd918..8feb29d 100644
--- a/server-tools/lake-lamp-authz/architecture-provision-broker.test.js
+++ b/server-tools/lake-lamp-authz/architecture-provision-broker.test.js
@@ -203,5 +203,15 @@ test("existing service update restores every changed file when acceptance fails"
     assert.equal(fs.readFileSync(path.join(installRoot, "server.js"), "utf8"), "old server\n");
     assert.equal(fs.existsSync(path.join(installRoot, "alias.json")), false);
     assert.equal(fs.readFileSync(path.join(unitDir, "guanghu-ai-discovery.service"), "utf8"), "old unit\n");
+    const retry = await provision({ target: "JD-FD-PRIMARY", action: "provision-approved-architecture", resource: `${updateRequestId}@${commit}` }, {
+      repoDir, releasesDir, unitDir, receiptsDir, installRootOverride: installRoot,
+      run: async (file, args) => ({ stdout: args.includes("rev-parse") ? `${commit}\n` : "" }),
+      getJson: async () => ({ ok: true }),
+      healthAttempts: 1,
+      healthDelayMs: 0,
+    });
+    assert.equal(retry.ok, true);
+    assert.equal(fs.readFileSync(path.join(installRoot, "server.js"), "utf8"), "new server\n");
+    assert.equal(fs.existsSync(path.join(installRoot, "alias.json")), true);
   } finally { fs.rmSync(root, { recursive: true, force: true }); }
 });