test(isolation): fix shard-order flakes exposed by #1972's new test files

Adding 3 new test files reshuffled the hash-based shards, exposing two
pre-existing test-isolation bugs:

- cycle-consolidate.test.ts assumed the global legacy-embedding preload's
  1536-d gateway config still held at initSchema, but a co-sharded test that
  calls resetGateway() in teardown nulls it, so initSchema fell back to the
  1280-d default and built a halfvec(1280) facts column its 1536-d fixtures
  can't fill. Re-pin the legacy OpenAI/1536 config in beforeAll (the pattern
  legacy-embedding-preload.ts documents for 1536-d fixture tests).
- db-lock-heartbeat-takeover.test.ts (merged from master's #1794) mutated
  process.env.GBRAIN_LOCK_STEAL_GRACE_SECONDS raw, tripping check:test-isolation
  rule R1. Convert to withEnv().

test/cycle-consolidate.test.ts

@@ -10,6 +10,7 @@
 
 import { describe, test, expect, beforeAll, afterAll, beforeEach } from 'bun:test';
 import { PGLiteEngine } from '../src/core/pglite-engine.ts';
+import { configureGateway } from '../src/core/ai/gateway.ts';
 import { runPhaseConsolidate } from '../src/core/cycle/phases/consolidate.ts';
 
 let engine: PGLiteEngine;
@@ -17,6 +18,20 @@ let engine: PGLiteEngine;
 beforeAll(async () => {
   engine = new PGLiteEngine();
   await engine.connect({});
+  // initSchema() bakes the facts.embedding dim from the gateway's configured
+  // embedding model; the default is now 1280-d (ZE). This file's fixtures are
+  // 1536-d, so pin the legacy 1536-d OpenAI config (matching
+  // test/helpers/legacy-embedding-preload.ts) right before initSchema. The
+  // global preload sets this, but a co-sharded test that calls resetGateway()
+  // in its teardown nulls it, leaving initSchema to fall back to the 1280-d
+  // default and build a halfvec(1280) column the 1536-d inserts can't fill.
+  // Re-pinning here makes the schema deterministic regardless of shard
+  // neighbors (surfaced when #1972's new test files reshuffled the shards).
+  configureGateway({
+    embedding_model: 'openai:text-embedding-3-large',
+    embedding_dimensions: 1536,
+    env: { ...process.env },
+  });
   await engine.initSchema();
 });
 

test/db-lock-heartbeat-takeover.test.ts

@@ -16,6 +16,7 @@
 import { describe, test, expect, beforeAll, afterAll, beforeEach } from 'bun:test';
 import { hostname } from 'os';
 import { PGLiteEngine } from '../src/core/pglite-engine.ts';
+import { withEnv } from './helpers/with-env.ts';
 import {
   tryAcquireDbLock,
   resolveStealGraceSeconds,
@@ -81,22 +82,16 @@ describe('resolveStealGraceSeconds', () => {
     expect(resolveStealGraceSeconds(1)).toBe(60);
   });
 
-  test('env override wins', () => {
-    process.env.GBRAIN_LOCK_STEAL_GRACE_SECONDS = '123';
-    try {
+  test('env override wins', async () => {
+    await withEnv({ GBRAIN_LOCK_STEAL_GRACE_SECONDS: '123' }, async () => {
       expect(resolveStealGraceSeconds(30)).toBe(123);
-    } finally {
-      delete process.env.GBRAIN_LOCK_STEAL_GRACE_SECONDS;
-    }
+    });
   });
 
-  test('bad env override falls back to derived', () => {
-    process.env.GBRAIN_LOCK_STEAL_GRACE_SECONDS = 'nope';
-    try {
+  test('bad env override falls back to derived', async () => {
+    await withEnv({ GBRAIN_LOCK_STEAL_GRACE_SECONDS: 'nope' }, async () => {
       expect(resolveStealGraceSeconds(30)).toBe(600);
-    } finally {
-      delete process.env.GBRAIN_LOCK_STEAL_GRACE_SECONDS;
-    }
+    });
   });
 });