diff --git a/bin/gstack-gbrain-detect b/bin/gstack-gbrain-detect
index 66503905e4..897bec2431 100755
--- a/bin/gstack-gbrain-detect
+++ b/bin/gstack-gbrain-detect
@@ -18,7 +18,8 @@
  *     "gstack_brain_sync_mode": "off"|"artifacts-only"|"full",
  *     "gstack_brain_git": true|false,
  *     "gstack_artifacts_remote": "https://..." | "",
- *     "gbrain_local_status": "ok"|"no-cli"|"missing-config"|"broken-config"|"broken-db"
+ *     "gbrain_local_status": "ok"|"no-cli"|"missing-config"|"broken-config"|"broken-db",
+ *     "gbrain_pooler_mode": "transaction"|"session"|null
  *   }
  *
  * Backward compatibility (per plan codex #5): the 9 pre-existing fields stay
@@ -42,6 +43,7 @@ import {
   resolveGbrainBin,
   readGbrainVersion,
 } from "../lib/gbrain-local-status";
+import { isTransactionModePooler } from "../lib/gbrain-exec";
 
 const STATE_DIR = process.env.GSTACK_HOME || join(userHome(), ".gstack");
 const SCRIPT_DIR = __dirname;
@@ -98,6 +100,17 @@ function detectConfig(): { exists: boolean; engine: "pglite" | "postgres" | null
   return { exists: true, engine: null };
 }
 
+// --- pooler mode detection (#1435) ---
+//
+// Reads DATABASE_URL from ~/.gbrain/config.json and checks whether it targets
+// a PgBouncer transaction-mode pooler (port 6543). Surfaced so /sync-gbrain
+// and /setup-gbrain can advise users when search may require GBRAIN_PREPARE.
+function detectPoolerMode(): "transaction" | "session" | "unknown" | null {
+  const parsed = tryReadJSON(GBRAIN_CONFIG) as { database_url?: string } | null;
+  if (!parsed?.database_url) return null;
+  return isTransactionModePooler(parsed.database_url) ? "transaction" : "session";
+}
+
 // --- gbrain doctor health (any nonzero exit or non-"ok"/"warnings" status → false) ---
 //
 // Uses --fast to avoid hanging on a dead DB. Per the local-status classifier
@@ -215,6 +228,7 @@ function main(): void {
     gstack_brain_git: detectBrainGit(),
     gstack_artifacts_remote: detectArtifactsRemote(),
     gbrain_local_status: localEngineStatus({ noCache }),
+    gbrain_pooler_mode: detectPoolerMode(),
   };
 
   process.stdout.write(JSON.stringify(out, null, 2) + "\n");
diff --git a/lib/gbrain-exec.ts b/lib/gbrain-exec.ts
index 5b768749f8..4568ef41ae 100644
--- a/lib/gbrain-exec.ts
+++ b/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;
 }
 
diff --git a/sync-gbrain/SKILL.md b/sync-gbrain/SKILL.md
index f7b9b52305..8525b55f54 100644
--- a/sync-gbrain/SKILL.md
+++ b/sync-gbrain/SKILL.md
@@ -905,13 +905,25 @@ Capability check (per /plan-eng-review §6):
 
 ```bash
 SLUG="_capability_check_$$"
+CAPABILITY_OK=0
 if [ -f ~/.gbrain/config.json ] && \
-   gbrain --version 2>/dev/null | grep -q '^gbrain ' && \
-   echo "ping" | gbrain put "$SLUG" >/dev/null 2>&1 && \
-   gbrain search "ping" 2>/dev/null | grep -q "$SLUG"; then
-  CAPABILITY_OK=1
-else
-  CAPABILITY_OK=0
+   gbrain --version 2>/dev/null | grep -q '^gbrain '; then
+  # GBRAIN_PREPARE=true ensures prepared statements stay enabled when
+  # connecting through a PgBouncer transaction-mode pooler (port 6543).
+  # Without it, search silently returns no results (#1435).
+  export GBRAIN_PREPARE=true
+  if echo "ping" | gbrain put "$SLUG" >/dev/null 2>&1; then
+    # Retry search up to 3 times with 1s delay — under transaction-mode
+    # pooling the search index may not be visible on the next connection
+    # immediately after the put.
+    for _attempt in 1 2 3; do
+      if gbrain search "ping" 2>/dev/null | grep -q "$SLUG"; then
+        CAPABILITY_OK=1
+        break
+      fi
+      sleep 1
+    done
+  fi
 fi
 gbrain delete "$SLUG" 2>/dev/null || true
 ```
diff --git a/sync-gbrain/SKILL.md.tmpl b/sync-gbrain/SKILL.md.tmpl
index b05c390664..73809d6dd2 100644
--- a/sync-gbrain/SKILL.md.tmpl
+++ b/sync-gbrain/SKILL.md.tmpl
@@ -185,13 +185,25 @@ Capability check (per /plan-eng-review §6):
 
 ```bash
 SLUG="_capability_check_$$"
+CAPABILITY_OK=0
 if [ -f ~/.gbrain/config.json ] && \
-   gbrain --version 2>/dev/null | grep -q '^gbrain ' && \
-   echo "ping" | gbrain put "$SLUG" >/dev/null 2>&1 && \
-   gbrain search "ping" 2>/dev/null | grep -q "$SLUG"; then
-  CAPABILITY_OK=1
-else
-  CAPABILITY_OK=0
+   gbrain --version 2>/dev/null | grep -q '^gbrain '; then
+  # GBRAIN_PREPARE=true ensures prepared statements stay enabled when
+  # connecting through a PgBouncer transaction-mode pooler (port 6543).
+  # Without it, search silently returns no results (#1435).
+  export GBRAIN_PREPARE=true
+  if echo "ping" | gbrain put "$SLUG" >/dev/null 2>&1; then
+    # Retry search up to 3 times with 1s delay — under transaction-mode
+    # pooling the search index may not be visible on the next connection
+    # immediately after the put.
+    for _attempt in 1 2 3; do
+      if gbrain search "ping" 2>/dev/null | grep -q "$SLUG"; then
+        CAPABILITY_OK=1
+        break
+      fi
+      sleep 1
+    done
+  fi
 fi
 gbrain delete "$SLUG" 2>/dev/null || true
 ```
diff --git a/test/build-gbrain-env.test.ts b/test/build-gbrain-env.test.ts
index 4066126d04..be7b8f54d8 100644
--- a/test/build-gbrain-env.test.ts
+++ b/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);
+  });
 });