fix(mcp): detect ambiguous model selection and return actionable 400

When displayName is absent and multiple configs share the same
provider+model, return a 400 that lists candidate displayNames instead
of silently picking the first match.

Matching logic:
- filter by provider+model to collect candidates
- if displayName provided: exact match on displayName within candidates
- if displayName absent and exactly one candidate: use it
- if displayName absent and multiple candidates: 400 with disambiguation hint

Author: a.dmitriev

packages/web/src/features/mcp/askCodebase.ts

@@ -57,17 +57,22 @@ export const askCodebase = (params: AskCodebaseParams): Promise<AskCodebaseResul
 
             let languageModelConfig = configuredModels[0];
             if (requestedLanguageModel) {
-                const matchingModel = configuredModels.find(
+                const candidates = configuredModels.filter(
                     (m) => m.provider === requestedLanguageModel.provider &&
-                           m.model === requestedLanguageModel.model &&
-                           (requestedLanguageModel.displayName === undefined ||
-                            m.displayName === requestedLanguageModel.displayName)
+                           m.model === requestedLanguageModel.model
                 );
+                const matchingModel = requestedLanguageModel.displayName
+                    ? candidates.find((m) => m.displayName === requestedLanguageModel.displayName)
+                    : candidates.length === 1 ? candidates[0] : undefined;
                 if (!matchingModel) {
+                    const ambiguous = !requestedLanguageModel.displayName && candidates.length > 1;
+                    const hint = ambiguous
+                        ? ` Multiple configurations found for this model. Provide a displayName to disambiguate: ${candidates.map((m) => m.displayName).join(', ')}.`
+                        : '';
                     return {
                         statusCode: StatusCodes.BAD_REQUEST,
                         errorCode: ErrorCode.INVALID_REQUEST_BODY,
-                        message: `Language model '${requestedLanguageModel.provider}/${requestedLanguageModel.model}' is not configured.`,
+                        message: `Language model '${requestedLanguageModel.provider}/${requestedLanguageModel.model}' is not configured.${hint}`,
                     } satisfies ServiceError;
                 }
                 languageModelConfig = matchingModel;