fix(mcp): match language model by provider+model, fall back when displayName absent

The MCP tool schema for ask_codebase omits displayName from the request
shape (@sourcebot/mcp uses .omit({ displayName: true })). When an LLM
agent selects a model it can only pass {provider, model}, so the previous
getLanguageModelKey-based match (which includes displayName) always
produced a key like 'anthropic-claude-opus-4-7-undefined' vs the
configured 'anthropic-claude-opus-4-7-Claude Opus 4.7', causing a 400
for any explicit model selection.

New logic: match on provider + model always; honour displayName only when
the caller actually provides it, preserving disambiguation between two
models that share the same provider/model but differ in displayName
(e.g. two opus-4-7 entries with different reasoningEffort).

Fixes #1137

Author: a.dmitriev

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

@@ -1,7 +1,7 @@
 import { sew } from "@/middleware/sew";
 import { getConfiguredLanguageModels, getAISDKLanguageModelAndOptions, generateChatNameFromMessage, updateChatMessages } from "@/features/chat/utils.server";
 import { LanguageModelInfo, SBChatMessage, SearchScope } from "@/features/chat/types";
-import { convertLLMOutputToPortableMarkdown, getAnswerPartFromAssistantMessage, getLanguageModelKey } from "@/features/chat/utils";
+import { convertLLMOutputToPortableMarkdown, getAnswerPartFromAssistantMessage } from "@/features/chat/utils";
 import { ErrorCode } from "@/lib/errorCodes";
 import { ServiceError, ServiceErrorException } from "@/lib/serviceError";
 import { withOptionalAuth } from "@/middleware/withAuth";
@@ -58,7 +58,10 @@ export const askCodebase = (params: AskCodebaseParams): Promise<AskCodebaseResul
             let languageModelConfig = configuredModels[0];
             if (requestedLanguageModel) {
                 const matchingModel = configuredModels.find(
-                    (m) => getLanguageModelKey(m) === getLanguageModelKey(requestedLanguageModel)
+                    (m) => m.provider === requestedLanguageModel.provider &&
+                           m.model === requestedLanguageModel.model &&
+                           (requestedLanguageModel.displayName === undefined ||
+                            m.displayName === requestedLanguageModel.displayName)
                 );
                 if (!matchingModel) {
                     return {