fix: detect PgBouncer transaction-mode pooler and set GBRAIN_PREPARE=true (#1435)

When gbrain connects through a PgBouncer transaction-mode pooler (port
6543), it auto-disables prepared statements. This breaks `gbrain search`
silently — the /sync-gbrain capability check fails and the GBrain Search
Guidance block never gets written to CLAUDE.md.

Three-layer fix:

1. **lib/gbrain-exec.ts** — `buildGbrainEnv()` now detects port 6543 in
   the effective DATABASE_URL and sets `GBRAIN_PREPARE=true` in the env
   passed to every gbrain spawn. This is the single chokepoint — all
   gstack gbrain invocations inherit the fix. Caller can opt out with
   `GBRAIN_PREPARE=false`.

2. **sync-gbrain/SKILL.md{,.tmpl}** — capability check now exports
   `GBRAIN_PREPARE=true` explicitly and retries search up to 3x with 1s
   delay for async index propagation under connection pooling.

3. **bin/gstack-gbrain-detect** — surfaces `gbrain_pooler_mode` field
   ("transaction" | "session" | null) in the preamble probe JSON so
   /setup-gbrain and /sync-gbrain can advise users about pooler state.

Closes #1435

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Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test/build-gbrain-env.test.ts

@@ -15,7 +15,7 @@ import { mkdtempSync, writeFileSync, mkdirSync, rmSync } from "fs";
 import { tmpdir } from "os";
 import { join } from "path";
 
-import { buildGbrainEnv } from "../lib/gbrain-exec";
+import { buildGbrainEnv, isTransactionModePooler } from "../lib/gbrain-exec";
 
 describe("buildGbrainEnv", () => {
   let home: string;
@@ -117,4 +117,74 @@ describe("buildGbrainEnv", () => {
     const result = buildGbrainEnv({ baseEnv });
     expect(result.DATABASE_URL).toBe("postgresql://gbrain/db");
   });
+
+  // --- GBRAIN_PREPARE auto-detection (#1435) ---
+
+  it("sets GBRAIN_PREPARE=true when DATABASE_URL targets port 6543 (transaction-mode pooler)", () => {
+    const poolerUrl = "postgresql://postgres.abc:pw@aws-0-us-east-1.pooler.supabase.com:6543/postgres";
+    writeFileSync(join(gbrainHome, "config.json"), JSON.stringify({ database_url: poolerUrl }));
+    const baseEnv = { HOME: home };
+    const result = buildGbrainEnv({ baseEnv });
+    expect(result.DATABASE_URL).toBe(poolerUrl);
+    expect(result.GBRAIN_PREPARE).toBe("true");
+  });
+
+  it("does not set GBRAIN_PREPARE when DATABASE_URL targets port 5432 (session-mode pooler)", () => {
+    const sessionUrl = "postgresql://postgres.abc:pw@aws-0-us-east-1.pooler.supabase.com:5432/postgres";
+    writeFileSync(join(gbrainHome, "config.json"), JSON.stringify({ database_url: sessionUrl }));
+    const baseEnv = { HOME: home };
+    const result = buildGbrainEnv({ baseEnv });
+    expect(result.GBRAIN_PREPARE).toBeUndefined();
+  });
+
+  it("does not set GBRAIN_PREPARE for pglite (no port in URL)", () => {
+    writeFileSync(join(gbrainHome, "config.json"), JSON.stringify({ database_url: "postgresql://gbrain/db" }));
+    const baseEnv = { HOME: home };
+    const result = buildGbrainEnv({ baseEnv });
+    expect(result.GBRAIN_PREPARE).toBeUndefined();
+  });
+
+  it("respects caller's explicit GBRAIN_PREPARE=false (opt-out)", () => {
+    const poolerUrl = "postgresql://postgres.abc:pw@aws-0-us-east-1.pooler.supabase.com:6543/postgres";
+    writeFileSync(join(gbrainHome, "config.json"), JSON.stringify({ database_url: poolerUrl }));
+    const baseEnv = { HOME: home, GBRAIN_PREPARE: "false" };
+    const result = buildGbrainEnv({ baseEnv });
+    expect(result.GBRAIN_PREPARE).toBe("false");
+  });
+
+  it("sets GBRAIN_PREPARE even when caller DATABASE_URL already matches config on port 6543", () => {
+    const poolerUrl = "postgresql://postgres.abc:pw@aws-0-us-east-1.pooler.supabase.com:6543/postgres";
+    writeFileSync(join(gbrainHome, "config.json"), JSON.stringify({ database_url: poolerUrl }));
+    const baseEnv = { HOME: home, DATABASE_URL: poolerUrl };
+    const result = buildGbrainEnv({ baseEnv });
+    expect(result.GBRAIN_PREPARE).toBe("true");
+  });
+});
+
+describe("isTransactionModePooler", () => {
+  it("returns true for Supabase transaction-mode pooler URL (port 6543)", () => {
+    expect(isTransactionModePooler(
+      "postgresql://postgres.abc:pw@aws-0-us-east-1.pooler.supabase.com:6543/postgres"
+    )).toBe(true);
+  });
+
+  it("returns false for session-mode pooler URL (port 5432)", () => {
+    expect(isTransactionModePooler(
+      "postgresql://postgres.abc:pw@aws-0-us-east-1.pooler.supabase.com:5432/postgres"
+    )).toBe(false);
+  });
+
+  it("returns false for pglite-style URL (no port)", () => {
+    expect(isTransactionModePooler("postgresql://gbrain/db")).toBe(false);
+  });
+
+  it("returns false for unparseable URL", () => {
+    expect(isTransactionModePooler("not-a-url")).toBe(false);
+  });
+
+  it("handles postgres:// scheme (without 'ql')", () => {
+    expect(isTransactionModePooler(
+      "postgres://postgres.abc:pw@host:6543/postgres"
+    )).toBe(true);
+  });
 });