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>

lib/gbrain-exec.ts

@@ -54,6 +54,26 @@ export interface BuildGbrainEnvOptions {
   announce?: boolean;
 }
 
+/**
+ * Detect whether a DATABASE_URL targets a PgBouncer transaction-mode pooler.
+ *
+ * Supabase transaction-mode poolers conventionally run on port 6543 at
+ * `*.pooler.supabase.com`. When gbrain connects through one of these, it
+ * auto-disables prepared statements — but search requires them (#1435).
+ * Returns `true` when the URL looks like a transaction-mode pooler so the
+ * caller can set `GBRAIN_PREPARE=true` to re-enable prepared statements.
+ */
+export function isTransactionModePooler(url: string): boolean {
+  try {
+    // DATABASE_URLs use postgresql:// scheme which URL() doesn't natively
+    // parse host/port from, so swap to http:// for reliable parsing.
+    const parsed = new URL(url.replace(/^postgres(ql)?:\/\//, "http://"));
+    return parsed.port === "6543";
+  } catch {
+    return false;
+  }
+}
+
 /**
  * Build an env dict with DATABASE_URL seeded from
  * `${GBRAIN_HOME:-$HOME/.gbrain}/config.json`. Returns the base env
@@ -63,6 +83,11 @@ export interface BuildGbrainEnvOptions {
  *   - the config has no `database_url`,
  *   - the caller already set DATABASE_URL to the same value.
  *
+ * When the effective DATABASE_URL targets a PgBouncer transaction-mode
+ * pooler (port 6543), sets `GBRAIN_PREPARE=true` so gbrain re-enables
+ * prepared statements needed for search (#1435). Caller can override
+ * with `GBRAIN_PREPARE=false` in the base env.
+ *
  * Always returns a fresh object — mutating the returned env never
  * affects the caller's env. Tests assert on effective values, not
  * object identity.
@@ -84,14 +109,31 @@ export function buildGbrainEnv(opts: BuildGbrainEnvOptions = {}): NodeJS.Process
     return out;
   }
   if (!cfg.database_url) return out;
-  if (baseEnv.DATABASE_URL === cfg.database_url) return out;
 
   const hadCaller = baseEnv.DATABASE_URL !== undefined;
-  out.DATABASE_URL = cfg.database_url;
-  if (opts.announce) {
-    const note = hadCaller ? " (overrode value from caller env / .env.local)" : "";
-    process.stderr.write(`[gbrain-exec] seeded DATABASE_URL from ${configPath}${note}\n`);
+  const alreadyMatch = baseEnv.DATABASE_URL === cfg.database_url;
+  if (!alreadyMatch) {
+    out.DATABASE_URL = cfg.database_url;
+    if (opts.announce) {
+      const note = hadCaller ? " (overrode value from caller env / .env.local)" : "";
+      process.stderr.write(`[gbrain-exec] seeded DATABASE_URL from ${configPath}${note}\n`);
+    }
   }
+
+  // PgBouncer transaction-mode pooler detection (#1435): when the effective
+  // DATABASE_URL targets port 6543 (Supabase transaction-mode convention),
+  // gbrain auto-disables prepared statements — but search needs them.
+  // Set GBRAIN_PREPARE=true unless the caller explicitly opted out.
+  const effectiveUrl = out.DATABASE_URL || cfg.database_url;
+  if (effectiveUrl && !out.GBRAIN_PREPARE && isTransactionModePooler(effectiveUrl)) {
+    out.GBRAIN_PREPARE = "true";
+    if (opts.announce) {
+      process.stderr.write(
+        `[gbrain-exec] set GBRAIN_PREPARE=true (port 6543 transaction-mode pooler detected)\n`,
+      );
+    }
+  }
+
   return out;
 }