fix: handle missing exception transforms in Mongo and Postgres adapters

- Mongo: extend createCollection pre-check to all collections in
  shared-tables mode, not just _metadata
- Postgres: add 42P01 (Undefined table) → NotFoundException in
  processException
- Postgres: wrap deleteCollection in try-catch with processException
  to match MariaDB behavior

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

Author: abnegate

src/Database/Adapter/Mongo.php

@@ -414,8 +414,10 @@ public function createCollection(string $name, array $attributes = [], array $in
     {
         $id = $this->getNamespace() . '_' . $this->filter($name);
 
-        // For metadata collections outside transactions, check if exists first
-        if (!$this->inTransaction && $name === Database::METADATA && $this->exists($this->getNamespace(), $name)) {
+        // In shared-tables mode or for metadata, the physical collection may
+        // already exist for another tenant. Return early to avoid a
+        // "Collection Exists" exception from the client.
+        if (!$this->inTransaction && ($this->getSharedTables() || $name === Database::METADATA) && $this->exists($this->getNamespace(), $name)) {
             return true;
         }
 

src/Database/Adapter/Postgres.php

@@ -439,7 +439,11 @@ public function deleteCollection(string $id): bool
         $sql = "DROP TABLE {$this->getSQLTable($id)}, {$this->getSQLTable($id . '_perms')}";
         $sql = $this->trigger(Database::EVENT_COLLECTION_DELETE, $sql);
 
-        return $this->getPDO()->prepare($sql)->execute();
+        try {
+            return $this->getPDO()->prepare($sql)->execute();
+        } catch (PDOException $e) {
+            throw $this->processException($e);
+        }
     }
 
     /**
@@ -2229,6 +2233,11 @@ protected function processException(PDOException $e): \Exception
             return new LimitException('Datetime field overflow', $e->getCode(), $e);
         }
 
+        // Unknown table
+        if ($e->getCode() === '42P01' && isset($e->errorInfo[1]) && $e->errorInfo[1] === 7) {
+            return new NotFoundException('Collection not found', $e->getCode(), $e);
+        }
+
         // Unknown column
         if ($e->getCode() === "42703" && isset($e->errorInfo[1]) && $e->errorInfo[1] === 7) {
             return new NotFoundException('Attribute not found', $e->getCode(), $e);

tests/e2e/Adapter/Scopes/CollectionTests.php

@@ -1393,14 +1393,13 @@ public function testSharedTablesMultiTenantCreateCollection(): void
         $col1Again = $database->getCollection($colName);
         $this->assertFalse($col1Again->isEmpty());
 
-        // Cleanup: delete per-tenant metadata docs
-        $database->setTenant($tenant1);
-        $database->deleteCollection($colName);
-        $database->setTenant($tenant2);
-        $database->deleteCollection($colName);
-
         if ($createdDb) {
             $database->delete();
+        } else {
+            $database->setTenant($tenant1);
+            $database->deleteCollection($colName);
+            $database->setTenant($tenant2);
+            $database->deleteCollection($colName);
         }
 
         $database