[Platform] Refactor model size variant logic into parseModelName

Move the size variant resolution logic from getModel() into parseModelName() for better separation of concerns. The parseModelName() method is now non-static and returns a catalogKey for lookups while preserving the full model name.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: OskarStark

src/platform/src/ModelCatalog/AbstractModelCatalog.php

@@ -32,38 +32,16 @@ public function getModel(string $modelName): Model
             throw new InvalidArgumentException('Model name cannot be empty.');
         }
 
-        $parsed = self::parseModelName($modelName);
+        $parsed = $this->parseModelName($modelName);
         $actualModelName = $parsed['name'];
+        $catalogKey = $parsed['catalogKey'];
         $options = $parsed['options'];
 
-        // Try to find the model directly first
-        if (!isset($this->models[$actualModelName])) {
-            // If not found and contains a colon (e.g., "model:23b"), try the base model name
-            if (str_contains($actualModelName, ':')) {
-                $baseModelName = explode(':', $actualModelName, 2)[0];
-
-                if (isset($this->models[$baseModelName])) {
-                    // Use the base model's config but keep the full model name
-                    $modelConfig = $this->models[$baseModelName];
-                    $modelClass = $modelConfig['class'];
-
-                    if (!class_exists($modelClass)) {
-                        throw new InvalidArgumentException(\sprintf('Model class "%s" does not exist.', $modelClass));
-                    }
-
-                    $model = new $modelClass($actualModelName, $modelConfig['capabilities'], $options);
-                    if (!$model instanceof Model) {
-                        throw new InvalidArgumentException(\sprintf('Model class "%s" must extend "%s".', $modelClass, Model::class));
-                    }
-
-                    return $model;
-                }
-            }
-
+        if (!isset($this->models[$catalogKey])) {
             throw new ModelNotFoundException(\sprintf('Model "%s" not found.', $actualModelName));
         }
 
-        $modelConfig = $this->models[$actualModelName];
+        $modelConfig = $this->models[$catalogKey];
         $modelClass = $modelConfig['class'];
 
         if (!class_exists($modelClass)) {
@@ -88,12 +66,13 @@ public function getModels(): array
 
     /**
      * Extracts model name and options from a model name string that may contain query parameters.
+     * Also resolves size variants (e.g., "model:23b") to their base model for catalog lookup.
      *
      * @param string $modelName The model name, potentially with query parameters (e.g., "model-name?param=value&other=123")
      *
-     * @return array{name: string, options: array<string, mixed>} An array containing the model name and parsed options
+     * @return array{name: string, catalogKey: string, options: array<string, mixed>} An array containing the model name, catalog lookup key, and parsed options
      */
-    protected static function parseModelName(string $modelName): array
+    protected function parseModelName(string $modelName): array
     {
         $options = [];
         $actualModelName = $modelName;
@@ -110,8 +89,18 @@ protected static function parseModelName(string $modelName): array
             $options = self::convertNumericStrings($options);
         }
 
+        // Determine catalog key: try exact match first, then fall back to base model
+        $catalogKey = $actualModelName;
+        if (!isset($this->models[$actualModelName]) && str_contains($actualModelName, ':')) {
+            $baseModelName = explode(':', $actualModelName, 2)[0];
+            if (isset($this->models[$baseModelName])) {
+                $catalogKey = $baseModelName;
+            }
+        }
+
         return [
             'name' => $actualModelName,
+            'catalogKey' => $catalogKey,
             'options' => $options,
         ];
     }