diff --git a/test/search/hybrid-reranker-integration.serial.test.ts b/test/search/hybrid-reranker-integration.serial.test.ts
index 3ba02c371..34344731e 100644
--- a/test/search/hybrid-reranker-integration.serial.test.ts
+++ b/test/search/hybrid-reranker-integration.serial.test.ts
@@ -31,9 +31,24 @@ import {
 } from '../../src/core/ai/gateway.ts';
 import type { PageInput, SearchOpts } from '../../src/core/types.ts';
 import type { RerankInput, RerankResult } from '../../src/core/ai/gateway.ts';
+import { mkdtempSync, rmSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
 
 let engine: PGLiteEngine;
 
+// These tests stub the gateway at 1536 dims (DIMS). Since v0.36.3.0 hybridSearch
+// resolves the embedding column via loadConfig(), whose precedence is
+// cfg.embedding_dimensions > gateway dims > default — so a contributor's real
+// ~/.gbrain/config.json (e.g. text-embedding-3-small at 1280) outranks the stub,
+// the 1536-d stub vector then fails the gateway dim check, search silently falls
+// back to keyword-only, and the reranker never runs (0 docs → 4 tests fail). CI
+// is green only because a fresh runner has no config file (#1527). Isolate
+// GBRAIN_HOME to an empty tmpdir so loadConfig() returns null and the stub's dims
+// win — same idiom as emptyHome() in test/ai/gateway-probe-chat-model.test.ts.
+let prevGbrainHome: string | undefined;
+let isolatedHome: string;
+
 const DIMS = 1536; // gateway default embedding dim
 const FAKE_EMB = Array.from({ length: DIMS }, (_, j) => (j === 0 ? 1 : 0.01));
 
@@ -44,6 +59,12 @@ function stubEmbeddings(): void {
 }
 
 beforeAll(async () => {
+  // Hermetic config home: ignore the machine's real ~/.gbrain so its
+  // embedding_dimensions can't outrank the 1536-d stub (see note above, #1527).
+  prevGbrainHome = process.env.GBRAIN_HOME;
+  isolatedHome = mkdtempSync(join(tmpdir(), 'gbrain-rerank-home-'));
+  process.env.GBRAIN_HOME = isolatedHome;
+
   engine = new PGLiteEngine();
   await engine.connect({});
   await engine.initSchema();
@@ -106,6 +127,9 @@ afterAll(async () => {
   __setEmbedTransportForTests(null);
   resetGateway();
   await engine.disconnect();
+  if (prevGbrainHome === undefined) delete process.env.GBRAIN_HOME;
+  else process.env.GBRAIN_HOME = prevGbrainHome;
+  rmSync(isolatedHome, { recursive: true, force: true });
 });
 
 describe('hybridSearch — reranker disabled (pass-through)', () => {