diff --git a/packages/local-config-updater/src/index.test.ts b/packages/local-config-updater/src/index.test.ts
index 370495618..f23888270 100644
--- a/packages/local-config-updater/src/index.test.ts
+++ b/packages/local-config-updater/src/index.test.ts
@@ -57,9 +57,30 @@ afterEach(() => {
   }
 });
 
+// Config with an import triggers the agent path (tryParseHexclaveConfigFileContent returns null)
+const CUSTOM_CONFIG = `import emailHtml from "./emails/welcome.html" with { type: "text" };
+export const config = { auth: { allowSignUp: true }, emails: { welcomeHtml: emailHtml } };
+`;
+
+describe("local config updater fast path", () => {
+  it("uses the fast path for plain static configs (no agent invoked)", async () => {
+    const configPath = writeTempConfig("export const config = { auth: { allowSignUp: true } };\n");
+    mockScriptedWrites = [{ tool_name: "Write", file_path: path.join(getTempDir(), "x.ts") }];
+
+    const { updateConfigObject } = await import("./index");
+
+    await expect(updateConfigObject(configPath, { "auth.allowSignUp": false })).resolves.toBeUndefined();
+
+    // Agent was never called, so no hook decisions were recorded
+    expect(mockHookDecisions).toEqual([]);
+    // The config file was updated deterministically
+    expect(readFileSync(configPath, "utf-8")).toContain('"allowSignUp": false');
+  });
+});
+
 describe("local config updater agent write boundary", () => {
   it("allows writes inside the config directory and captures them for rollback", async () => {
-    const configPath = writeTempConfig("export const config = { auth: { allowSignUp: true } };\n");
+    const configPath = writeTempConfig(CUSTOM_CONFIG);
     const inside = path.join(getTempDir(), "emails", "welcome-email.tsx");
     mockScriptedWrites = [{ tool_name: "Write", file_path: inside }];
     mockAfterWrites = () => {
@@ -74,7 +95,7 @@ describe("local config updater agent write boundary", () => {
   });
 
   it("denies a `../` escape and fails the run", async () => {
-    const configPath = writeTempConfig("export const config = { auth: { allowSignUp: true } };\n");
+    const configPath = writeTempConfig(CUSTOM_CONFIG);
     const outside = path.resolve(getTempDir(), "../../.env");
     mockScriptedWrites = [{ tool_name: "Write", file_path: outside }];
 
@@ -87,11 +108,11 @@ describe("local config updater agent write boundary", () => {
     expect(mockHookDecisions[0]).toMatchObject({
       hookSpecificOutput: { hookEventName: "PreToolUse", permissionDecision: "deny" },
     });
-    expect(readFileSync(configPath, "utf-8")).toBe("export const config = { auth: { allowSignUp: true } };\n");
+    expect(readFileSync(configPath, "utf-8")).toBe(CUSTOM_CONFIG);
   });
 
   it("denies an absolute path outside the config directory", async () => {
-    const configPath = writeTempConfig("export const config = { auth: { allowSignUp: true } };\n");
+    const configPath = writeTempConfig(CUSTOM_CONFIG);
     mockScriptedWrites = [{ tool_name: "Edit", file_path: "/etc/passwd" }];
 
     const { updateConfigObject } = await import("./index");
diff --git a/packages/local-config-updater/src/index.ts b/packages/local-config-updater/src/index.ts
index 05138ca7f..dda8846cc 100644
--- a/packages/local-config-updater/src/index.ts
+++ b/packages/local-config-updater/src/index.ts
@@ -2,7 +2,7 @@ import { showOnboardingHexclaveConfigValue } from "@hexclave/shared/dist/config-
 import { detectImportPackageFromDir, renderConfigFileContent } from "@hexclave/shared/dist/config-rendering";
 import type { Config, ConfigValue, NormalizedConfig } from "@hexclave/shared/dist/config/format";
 import { isValidConfig, normalize, override } from "@hexclave/shared/dist/config/format";
-import { getRelativeImportSpecifiers, hexclaveConfigFileExportsConfig } from "@hexclave/shared/dist/hexclave-config-file";
+import { getRelativeImportSpecifiers, hexclaveConfigFileExportsConfig, tryParseHexclaveConfigFileContent } from "@hexclave/shared/dist/hexclave-config-file";
 import { createHash } from "crypto";
 import { existsSync, mkdirSync, readFileSync, renameSync, rmSync, writeFileSync } from "fs";
 import { createJiti } from "jiti";
@@ -111,6 +111,21 @@ export async function updateConfigObject(configFilePath: string, configUpdate: C
   if (flattenConfigUpdate(configUpdate).length === 0) return;
 
   const content = readFileSync(configFilePath, "utf-8");
+
+  // Fast path: if the config is a plain static literal (no imports, no helpers),
+  // apply the update deterministically without invoking the AI agent.
+  const staticConfig = tryParseHexclaveConfigFileContent(content, configFilePath);
+  if (staticConfig != null && typeof staticConfig === "object" && isValidConfig(staticConfig)) {
+    const merged = override(staticConfig, configUpdate);
+    if (!isValidConfig(merged)) {
+      throw new Error(`${LOG_PREFIX} Merged config is invalid after applying update to ${configFilePath}`);
+    }
+    renderConfigObjectToFile(configFilePath, merged);
+    return;
+  }
+
+  // Agent path: config has custom structure (imports, helpers, external files)
+  // that must be preserved — delegate to the AI agent.
   const baselineConfig = await tryReadConfigForValidation(configFilePath);
   const snapshots = snapshotConfigFiles(configFilePath, content);
   try {