feat(auth): integrate authentication with installation lifecycle

backend/src/startup-error.ts

@@ -4,9 +4,15 @@ const STARTUP_CAUSES = new Set([
   "workspace_registry_invalid",
 ]);
 
+const EXACT_CAUSES = new Map([
+  ["authentication configuration is invalid", "auth_config_invalid"],
+  ["authentication session state is invalid", "auth_session_store_invalid"],
+  ["workspace registry configuration is invalid", "workspace_registry_invalid"],
+]);
+
 /** Return one bounded machine cause; never include the original error text or stack. */
 export function formatStartupFailure(error: unknown): string {
   const message = error instanceof Error ? error.message : "";
-  const cause = STARTUP_CAUSES.has(message) ? message : "startup_unknown";
+  const cause = STARTUP_CAUSES.has(message) ? message : EXACT_CAUSES.get(message) ?? "startup_unknown";
   return `backend startup failed: ${cause}`;
 }