fix(test): scope GSTACK_HOME to each file's execution window

Five files assigned process.env.GSTACK_HOME at module scope. Shard
processes evaluate sibling modules before running their tests, so the
assignment leaked into every other file in the shard — the damage was
already visible in defensive workarounds (relink.test.ts:28 'fresh
install test saw a neighbor's skill_prefix'; cdp-e2e's own comment
documents a sibling's temp dir baked into artifacts).

Pattern: save original, assign in beforeAll, restore in afterAll
(cdp-e2e already restored but still assigned at load — its window now
matches the others). GSTACK_TELEMETRY_OFF and GSTACK_PROJECT_SLUG get
the same treatment where they rode along. Victim files' defenses stay
in place (cheap insurance).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

browse/test/cdp-e2e.test.ts

@@ -24,14 +24,15 @@ const TMP_HOME = path.join(os.tmpdir(), `gstack-cdp-e2e-${process.pid}-${Date.no
 // which then got baked into artifacts that outlived it (dangling symlinks
 // into a deleted render dir). Save + restore in afterAll.
 const ORIGINAL_GSTACK_HOME = process.env.GSTACK_HOME;
-process.env.GSTACK_HOME = TMP_HOME;
+const ORIGINAL_TELEMETRY_OFF = process.env.GSTACK_TELEMETRY_OFF;
-process.env.GSTACK_TELEMETRY_OFF = '1'; // don't pollute analytics during tests
 
 let testServer: ReturnType<typeof startTestServer>;
 let bm: BrowserManager;
 let baseUrl: string;
 
 beforeAll(async () => {
+  process.env.GSTACK_HOME = TMP_HOME;
+  process.env.GSTACK_TELEMETRY_OFF = '1'; // don't pollute analytics during tests
   await fs.rm(TMP_HOME, { recursive: true, force: true });
   await fs.mkdir(TMP_HOME, { recursive: true });
   testServer = startTestServer(0);
@@ -44,6 +45,8 @@ beforeAll(async () => {
 afterAll(async () => {
   if (ORIGINAL_GSTACK_HOME === undefined) delete process.env.GSTACK_HOME;
   else process.env.GSTACK_HOME = ORIGINAL_GSTACK_HOME;
+  if (ORIGINAL_TELEMETRY_OFF === undefined) delete process.env.GSTACK_TELEMETRY_OFF;
+  else process.env.GSTACK_TELEMETRY_OFF = ORIGINAL_TELEMETRY_OFF;
   try { await bm.cleanup?.(); } catch {}
   try { testServer.server.stop(); } catch {}
   await fs.rm(TMP_HOME, { recursive: true, force: true });

browse/test/domain-skills-e2e.test.ts

@@ -17,8 +17,12 @@ import { startTestServer } from './test-server';
 import { BrowserManager } from '../src/browser-manager';
 
 const TMP_HOME = path.join(os.tmpdir(), `gstack-domain-e2e-${process.pid}-${Date.now()}`);
-process.env.GSTACK_HOME = TMP_HOME;
+
-process.env.GSTACK_PROJECT_SLUG = 'e2e-test-slug';
+// Scoped to this file's execution window — module-scope env assignment
+// leaks into sibling files in the shard process (see
+// test/gstack-home-module-scope.test.ts).
+const ORIGINAL_GSTACK_HOME = process.env.GSTACK_HOME;
+const ORIGINAL_PROJECT_SLUG = process.env.GSTACK_PROJECT_SLUG;
 
 let testServer: ReturnType<typeof startTestServer>;
 let bm: BrowserManager;
@@ -32,6 +36,8 @@ async function fakeBodyPipe(body: string): Promise<string> {
 }
 
 beforeAll(async () => {
+  process.env.GSTACK_HOME = TMP_HOME;
+  process.env.GSTACK_PROJECT_SLUG = 'e2e-test-slug';
   await fs.rm(TMP_HOME, { recursive: true, force: true });
   await fs.mkdir(path.join(TMP_HOME, 'projects', 'e2e-test-slug'), { recursive: true });
   testServer = startTestServer(0);
@@ -41,6 +47,10 @@ beforeAll(async () => {
 });
 
 afterAll(async () => {
+  if (ORIGINAL_GSTACK_HOME === undefined) delete process.env.GSTACK_HOME;
+  else process.env.GSTACK_HOME = ORIGINAL_GSTACK_HOME;
+  if (ORIGINAL_PROJECT_SLUG === undefined) delete process.env.GSTACK_PROJECT_SLUG;
+  else process.env.GSTACK_PROJECT_SLUG = ORIGINAL_PROJECT_SLUG;
   try { await bm.cleanup?.(); } catch {}
   try { testServer.server.stop(); } catch {}
   await fs.rm(TMP_HOME, { recursive: true, force: true });

browse/test/domain-skills-storage.test.ts

@@ -1,10 +1,22 @@
-import { describe, it, expect, beforeEach } from 'bun:test';
+import { describe, it, expect, beforeAll, beforeEach, afterAll } from 'bun:test';
 import { promises as fs } from 'fs';
 import * as path from 'path';
 import * as os from 'os';
 
 const TMP_HOME = path.join(os.tmpdir(), `gstack-test-${process.pid}-${Date.now()}`);
-process.env.GSTACK_HOME = TMP_HOME;
+
+// Scoped to this file's execution window — module-scope env assignment
+// leaks into sibling files in the shard process (see
+// test/gstack-home-module-scope.test.ts). freshImport() below runs inside
+// tests, so the beforeAll value is what ../src/domain-skills reads.
+const ORIGINAL_GSTACK_HOME = process.env.GSTACK_HOME;
+beforeAll(() => {
+  process.env.GSTACK_HOME = TMP_HOME;
+});
+afterAll(() => {
+  if (ORIGINAL_GSTACK_HOME === undefined) delete process.env.GSTACK_HOME;
+  else process.env.GSTACK_HOME = ORIGINAL_GSTACK_HOME;
+});
 
 // Re-import after env var set so module reads updated GSTACK_HOME
 async function freshImport() {

browse/test/telemetry.test.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect, beforeEach, afterAll } from 'bun:test';
+import { describe, it, expect, beforeAll, beforeEach, afterAll } from 'bun:test';
 import { promises as fs } from 'fs';
 import * as path from 'path';
 import * as os from 'os';
@@ -8,8 +8,21 @@ const TELEMETRY_FILE = path.join(TMP_HOME, 'analytics', 'browse-telemetry.jsonl'
 
 // Use GSTACK_HOME env to redirect telemetry writes (read each call,
 // not cached at module-load).
-process.env.GSTACK_HOME = TMP_HOME;
+// Scoped to this file's execution window — module-scope env assignment
-process.env.GSTACK_TELEMETRY_OFF = '0';
+// leaks into sibling files in the shard process (see
+// test/gstack-home-module-scope.test.ts).
+const ORIGINAL_GSTACK_HOME = process.env.GSTACK_HOME;
+const ORIGINAL_TELEMETRY_OFF = process.env.GSTACK_TELEMETRY_OFF;
+beforeAll(() => {
+  process.env.GSTACK_HOME = TMP_HOME;
+  process.env.GSTACK_TELEMETRY_OFF = '0';
+});
+afterAll(() => {
+  if (ORIGINAL_GSTACK_HOME === undefined) delete process.env.GSTACK_HOME;
+  else process.env.GSTACK_HOME = ORIGINAL_GSTACK_HOME;
+  if (ORIGINAL_TELEMETRY_OFF === undefined) delete process.env.GSTACK_TELEMETRY_OFF;
+  else process.env.GSTACK_TELEMETRY_OFF = ORIGINAL_TELEMETRY_OFF;
+});
 
 beforeEach(async () => {
   await fs.rm(TMP_HOME, { recursive: true, force: true });

test/helpers/budget-override.test.ts

@@ -8,16 +8,28 @@
  * timestamp + scope + reason + CI provenance.
  */
 
-import { describe, test, expect, beforeEach } from 'bun:test';
+import { describe, test, expect, beforeAll, beforeEach, afterAll } from 'bun:test';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as os from 'os';
 import { logBudgetOverride } from './budget-override';
 
 const TMP_HOME = fs.mkdtempSync(path.join(os.tmpdir(), 'budget-override-test-'));
-process.env.GSTACK_HOME = TMP_HOME;
 const AUDIT_PATH = path.join(TMP_HOME, 'analytics', 'spend-overrides.jsonl');
 
+// GSTACK_HOME is scoped to this file's execution window (beforeAll/afterAll),
+// never set at module load: bun evaluates sibling modules before running
+// their tests, so a module-scope assignment leaks into every other file in
+// the shard process (pinned by test/gstack-home-module-scope.test.ts).
+const ORIGINAL_GSTACK_HOME = process.env.GSTACK_HOME;
+beforeAll(() => {
+  process.env.GSTACK_HOME = TMP_HOME;
+});
+afterAll(() => {
+  if (ORIGINAL_GSTACK_HOME === undefined) delete process.env.GSTACK_HOME;
+  else process.env.GSTACK_HOME = ORIGINAL_GSTACK_HOME;
+});
+
 describe('logBudgetOverride', () => {
   beforeEach(() => {
     // Start each test with a clean audit file