fix(auth): pin native auth storage operations

backend/test/auth-test-fixtures.ts

@@ -5,6 +5,7 @@ import type { FastifyInstance } from "fastify";
 import { stringify } from "yaml";
 import { buildApp, type BuildAppDeps } from "../src/app.js";
 import { loadConfig } from "../src/config.js";
+import { createFixturePosixAuthStorageBridge } from "./fixtures/posix-auth-storage-bridge.mjs";
 
 export const localPassword = "correct horse battery staple";
 export const localPasswordHash = "$argon2id$v=19$m=65536,t=3,p=1$AAECAwQFBgcICQoLDA0ODw$DRo8ZSPI8G5OCvnFFapbVEjP69aDjy1Sw9i2743cPC4";
@@ -47,6 +48,11 @@ export function prepareAuthStateRoot(root: string): void {
   }
 }
 
+/** Explicit test-only substitute for the production tht-backed POSIX storage bridge. */
+export function createFixtureAuthStorageBridge() {
+  return createFixturePosixAuthStorageBridge();
+}
+
 /** Creates a production-local app and authenticates through the real login/session boundary. */
 export async function createLocalAuthFixture(
   deps?: BuildAppDeps,
@@ -82,11 +88,17 @@ export async function createLocalAuthFixture(
 
   const authStateRoot = join(directory, "auth-state");
   prepareAuthStateRoot(authStateRoot);
-  const app = buildApp(loadConfig({
-    THT_AUTH_CONFIG_FILE: authConfigFile,
-    THT_AUTH_STATE_ROOT: authStateRoot,
-    THT_HARNESS_DIR: "/tmp/h",
-  }), deps);
+  const app = buildApp(
+    loadConfig({
+      THT_AUTH_CONFIG_FILE: authConfigFile,
+      THT_AUTH_STATE_ROOT: authStateRoot,
+      THT_HARNESS_DIR: "/tmp/h",
+    }),
+    {
+      ...deps,
+      authStorageBridgeForTest: deps?.authStorageBridgeForTest ?? createFixtureAuthStorageBridge(),
+    },
+  );
   let downstream = 0;
   app.addHook("preHandler", async () => { downstream += 1; });