fix(test): hermetically exercise auth workflows

backend/src/pi/enabled-models.ts

@@ -1,6 +1,6 @@
 import { readFileSync } from "node:fs";
 import { homedir } from "node:os";
-import { join } from "node:path";
+import { join, resolve } from "node:path";
 
 export interface PiEnabledModelsResult {
   ids: string[];
@@ -43,7 +43,8 @@ function isExactCompositeId(value: unknown): value is string {
 export function loadPiEnabledModels(opts: LoadOptions): PiEnabledModelsResult {
   const warnings: string[] = [];
   const read = opts.read ?? ((path: string) => readFileSync(path, "utf8"));
-  const agentDir = opts.agentDir ?? join(homedir(), ".pi", "agent");
+  const agentDir = opts.agentDir
+    ?? resolve(process.env.PI_CODING_AGENT_DIR ?? join(homedir(), ".pi", "agent"));
   const globalPath = join(agentDir, "settings.json");
   const projectPath = join(opts.harnessDir, ".pi", "settings.json");
   const globalSettings = readSettings(globalPath, false, read, warnings);