Merge branch 'master' into fix/backlog-c60

The four "reranker enabled (reorder)" cases stub the gateway at 1536 dims,
but hybridSearch resolves the embedding column via loadConfig(), whose
precedence puts cfg.embedding_dimensions above the gateway stub. On any
machine whose ~/.gbrain/config.json sets a different dimension (e.g. 1280),
the stub vector fails the dim check, search silently degrades to
keyword-only, and the reranker never fires — deterministic 4-test failure
for contributors, green in CI only because fresh runners have no config.

Fix (test-only): point GBRAIN_HOME at an empty tmpdir in beforeAll so
loadConfig() returns null and the stub's dims win; restore + clean up in
afterAll. Same idiom as emptyHome() in
test/ai/gateway-probe-chat-model.test.ts.

Verified with a planted 1280-dim config.json: 2 pass / 4 fail before,
6 pass / 0 fail after; still 6/6 with no config. typecheck clean.

Takeover of #2640.

Co-authored-by: Willisbest <Willisbest@users.noreply.github.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/search/hybrid-reranker-integration.serial.test.ts

@@ -27,9 +27,24 @@ 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));
 
@@ -40,6 +55,12 @@ 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();
@@ -85,6 +106,9 @@ 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)', () => {