fix: only swallow client-level Collection Exists for shared-table/metadata paths

The code-0 "Collection Exists" from the Mongo client was being
converted to DuplicateException in processException, which the local
catch in createCollection silently returned true for — bypassing
Database::createCollection()'s orphan reconciliation in non-shared
mode. Move the handling into createCollection itself where context
is available: return true for shared-tables/metadata, throw
DuplicateException otherwise so the caller can reconcile.

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

Author: abnegate

src/Database/Adapter/Mongo.php

@@ -430,6 +430,16 @@ public function createCollection(string $name, array $attributes = [], array $in
             if ($e instanceof DuplicateException) {
                 return true;
             }
+            // Client throws code-0 "Collection Exists" when its pre-check
+            // finds the collection. In shared-tables/metadata context this
+            // is a no-op; otherwise re-throw as DuplicateException so
+            // Database::createCollection() can run orphan reconciliation.
+            if ($e->getCode() === 0 && stripos($e->getMessage(), 'Collection Exists') !== false) {
+                if ($this->getSharedTables() || $name === Database::METADATA) {
+                    return true;
+                }
+                throw new DuplicateException('Collection already exists', $e->getCode(), $e);
+            }
             throw $e;
         }
 
@@ -3520,8 +3530,8 @@ protected function processException(\Throwable $e): \Throwable
             return new DuplicateException('Document already exists', $e->getCode(), $e);
         }
 
-        // Collection already exists (code 48 from MongoDB, code 0 from client pre-check)
-        if ($e->getCode() === 48 || ($e->getCode() === 0 && stripos($e->getMessage(), 'Collection Exists') !== false)) {
+        // Collection already exists
+        if ($e->getCode() === 48) {
             return new DuplicateException('Collection already exists', $e->getCode(), $e);
         }