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>

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
 ```

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
 ```