feat: quota-aware subagent model fallback chain (#374)

src/codex/paths.ts

@@ -29,6 +29,11 @@ export const CODEX_PROFILE_PATH = join(CODEX_HOME, "opencodex.config.toml");
 export const DEFAULT_CATALOG_PATH = join(CODEX_HOME, "opencodex-catalog.json");
 export const CODEX_MODELS_CACHE_PATH = join(CODEX_HOME, "models_cache.json");
 
+/** Runtime CODEX_HOME lookup (honors CODEX_HOME env changes after import). */
+export function getCodexHome(): string {
+  return resolveCodexHome();
+}
+
 export function tomlString(value: string): string {
   return JSON.stringify(value);
 }

src/codex/routing.ts

@@ -391,7 +391,7 @@ function getEligiblePoolAccounts(config: OcxConfig, excludeId?: string, now = Da
   return ids;
 }
 
-function getPoolAccountPlan(config: OcxConfig, accountId: string): string | undefined {
+export function getPoolAccountPlan(config: OcxConfig, accountId: string): string | undefined {
   if (accountId === MAIN_CODEX_ACCOUNT_ID) return getMainAccountPlan();
   return (config.codexAccounts ?? []).find(account => !account.isMain && account.id === accountId)?.plan;
 }