fix: clear stale tenant model ids (#18210)

### Summary

Clear the paired tenant model ID when a model selection is explicitly
cleared in a whitelisted API request.

Replaces #18205.

Co-authored-by: Jin Hai <haijin.chn@gmail.com>

web/src/utils/llm-util.ts

@@ -201,17 +201,26 @@ export function addTenantParams(data: any, url?: string): any {
     return data;
   }
 
-  const llmList = getCachedLlmList();
-  if (!llmList) return data;
-
   // Handle arrays
   if (Array.isArray(data)) {
     return data.map((item) => addTenantParams(item, url));
   }
 
   const newData = { ...data };
+  const llmList = getCachedLlmList();
+
+  // Clear the paired tenant ID when a model selection is explicitly cleared.
+  for (const [paramName, tenantParamName] of Object.entries(modelParamMap)) {
+    if (
+      Object.hasOwn(newData, paramName) &&
+      (newData[paramName] === '' || newData[paramName] == null)
+    ) {
+      newData[tenantParamName] = null;
+    }
+  }
+
+  if (!llmList) return newData;
 
-  // Iterate through model parameters and add corresponding tenant parameters
   for (const [paramName, tenantParamName] of Object.entries(modelParamMap)) {
     if (newData[paramName]) {
       try {

web/src/utils/tests/llm-util.test.ts

@@ -1,4 +1,5 @@
 import {
+  addTenantParams,
   buildModelValue,
   getEmbeddingBaseName,
   parseModelUuid,
@@ -160,3 +161,29 @@ describe('getEmbeddingBaseName — dataset co-selection grouping', () => {
     expect(getEmbeddingBaseName(undefined)).toBe('');
   });
 });
+
+describe('addTenantParams — clearing model selections', () => {
+  test('clears a stale tenant rerank model id when rerank is explicitly cleared', () => {
+    expect(
+      addTenantParams(
+        {
+          rerank_id: '',
+          tenant_rerank_id: 'stale-tenant-model-id',
+        },
+        '/api/v1/chats/chat-id',
+      ),
+    ).toEqual({
+      rerank_id: '',
+      tenant_rerank_id: null,
+    });
+  });
+
+  test('preserves the tenant rerank model id when rerank is not part of the request', () => {
+    expect(
+      addTenantParams(
+        { tenant_rerank_id: 'existing-tenant-model-id' },
+        '/api/v1/chats/chat-id',
+      ),
+    ).toEqual({ tenant_rerank_id: 'existing-tenant-model-id' });
+  });
+});