fix: Differentiate duplicate ID vs unique index exceptions, fix Pool transaction pinning

- Mongo, Postgres, SQLite adapters now return distinct messages for duplicate document ID
  ("Document already exists") vs unique index violations ("Document with the requested
  unique attributes already exists"), matching MariaDB behavior
- Pool adapter now pins a single connection for the entire withTransaction lifecycle,
  ensuring all delegate calls within a transaction use the same underlying connection

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: abnegate

src/Database/Adapter/Mongo.php

@@ -3483,12 +3483,11 @@ protected function processException(\Throwable $e): \Throwable
         }
 
         // Duplicate key error
-        if ($e->getCode() === 11000) {
-            return new DuplicateException('Document already exists', $e->getCode(), $e);
-        }
-
-        // Duplicate key error for unique index
-        if ($e->getCode() === 11001) {
+        if ($e->getCode() === 11000 || $e->getCode() === 11001) {
+            $message = $e->getMessage();
+            if (!\str_contains($message, '_uid')) {
+                return new DuplicateException('Document with the requested unique attributes already exists', $e->getCode(), $e);
+            }
             return new DuplicateException('Document already exists', $e->getCode(), $e);
         }
 

src/Database/Adapter/Pool.php

@@ -16,6 +16,12 @@ class Pool extends Adapter
      */
     protected UtopiaPool $pool;
 
+    /**
+     * When a transaction is active, all delegate calls are routed through
+     * this pinned adapter to ensure they run on the same connection.
+     */
+    protected ?Adapter $pinnedAdapter = null;
+
     /**
      * @param UtopiaPool<covariant Adapter> $pool The pool to use for connections. Must contain instances of Adapter.
      */
@@ -36,6 +42,10 @@ public function __construct(UtopiaPool $pool)
      */
     public function delegate(string $method, array $args): mixed
     {
+        if ($this->pinnedAdapter !== null) {
+            return $this->pinnedAdapter->{$method}(...$args);
+        }
+
         return $this->pool->use(function (Adapter $adapter) use ($method, $args) {
             // Run setters in case config changed since this connection was last used
             $adapter->setDatabase($this->getDatabase());
@@ -123,7 +133,12 @@ public function withTransaction(callable $callback): mixed
                 $adapter->setMetadata($key, $value);
             }
 
-            return $adapter->withTransaction($callback);
+            $this->pinnedAdapter = $adapter;
+            try {
+                return $adapter->withTransaction($callback);
+            } finally {
+                $this->pinnedAdapter = null;
+            }
         });
     }
 

src/Database/Adapter/Postgres.php

@@ -2189,6 +2189,10 @@ protected function processException(PDOException $e): \Exception
 
         // Duplicate row
         if ($e->getCode() === '23505' && isset($e->errorInfo[1]) && $e->errorInfo[1] === 7) {
+            $message = $e->getMessage();
+            if (!\str_contains($message, '_uid')) {
+                return new DuplicateException('Document with the requested unique attributes already exists', $e->getCode(), $e);
+            }
             return new DuplicateException('Document already exists', $e->getCode(), $e);
         }
 

src/Database/Adapter/SQLite.php

@@ -1328,6 +1328,9 @@ protected function processException(PDOException $e): \Exception
                 stripos($message, 'unique') !== false ||
                 stripos($message, 'duplicate') !== false
             ) {
+                if (!\str_contains($message, '_uid')) {
+                    return new DuplicateException('Document with the requested unique attributes already exists', $e->getCode(), $e);
+                }
                 return new DuplicateException('Document already exists', $e->getCode(), $e);
             }
         }