🏷️ fix: Clear ModelSpec Display Fields When Navigating via Agent Share Link (#12274)

- Extract `specDisplayFieldReset` constant and `mergeQuerySettingsWithSpec`
  utility to `client/src/utils/endpoints.ts` as a single source of truth
  for spec display fields that must be cleared on non-spec transitions.
- Clear `spec`, `iconURL`, `modelLabel`, and `greeting` from the merged
  preset in `ChatRoute.getNewConvoPreset()` when URL query parameters
  override the conversation without explicitly setting a spec.
- Also clear `greeting` in the parallel cleanup in `useQueryParams.newQueryConvo`
  using the shared `specDisplayFieldReset` constant.
- Guard the field reset on `specPreset != null` so null values aren't
  injected when no spec is configured.
- Add comprehensive test coverage for the merge-and-clear logic.

client/src/utils/__tests__/mergeQuerySettingsWithSpec.test.ts

@@ -0,0 +1,152 @@
+import { EModelEndpoint } from 'librechat-data-provider';
+import type { TPreset } from 'librechat-data-provider';
+import { mergeQuerySettingsWithSpec, specDisplayFieldReset } from '../endpoints';
+
+describe('mergeQuerySettingsWithSpec', () => {
+  const specPreset: TPreset = {
+    endpoint: EModelEndpoint.openAI,
+    model: 'gpt-4',
+    spec: 'my-spec',
+    iconURL: 'https://example.com/icon.png',
+    modelLabel: 'My Custom GPT',
+    greeting: 'Hello from the spec!',
+    temperature: 0.7,
+  };
+
+  describe('when specPreset is active and query has no spec', () => {
+    it('clears all spec display fields for agent share links', () => {
+      const querySettings: TPreset = {
+        agent_id: 'agent_123',
+        endpoint: EModelEndpoint.agents,
+      };
+
+      const result = mergeQuerySettingsWithSpec(specPreset, querySettings);
+
+      expect(result.agent_id).toBe('agent_123');
+      expect(result.endpoint).toBe(EModelEndpoint.agents);
+      expect(result.spec).toBeNull();
+      expect(result.iconURL).toBeNull();
+      expect(result.modelLabel).toBeNull();
+      expect(result.greeting).toBeUndefined();
+    });
+
+    it('preserves non-display settings from the spec base', () => {
+      const querySettings: TPreset = {
+        agent_id: 'agent_123',
+        endpoint: EModelEndpoint.agents,
+      };
+
+      const result = mergeQuerySettingsWithSpec(specPreset, querySettings);
+
+      expect(result.temperature).toBe(0.7);
+    });
+
+    it('clears spec display fields for assistant share links', () => {
+      const querySettings: TPreset = {
+        assistant_id: 'asst_abc',
+        endpoint: EModelEndpoint.assistants,
+      };
+
+      const result = mergeQuerySettingsWithSpec(specPreset, querySettings);
+
+      expect(result.assistant_id).toBe('asst_abc');
+      expect(result.endpoint).toBe(EModelEndpoint.assistants);
+      expect(result.spec).toBeNull();
+      expect(result.iconURL).toBeNull();
+      expect(result.modelLabel).toBeNull();
+      expect(result.greeting).toBeUndefined();
+    });
+
+    it('clears spec display fields for model override links', () => {
+      const querySettings: TPreset = {
+        model: 'claude-sonnet-4-20250514',
+        endpoint: EModelEndpoint.anthropic,
+      };
+
+      const result = mergeQuerySettingsWithSpec(specPreset, querySettings);
+
+      expect(result.model).toBe('claude-sonnet-4-20250514');
+      expect(result.endpoint).toBe(EModelEndpoint.anthropic);
+      expect(result.spec).toBeNull();
+      expect(result.iconURL).toBeNull();
+      expect(result.modelLabel).toBeNull();
+      expect(result.greeting).toBeUndefined();
+    });
+  });
+
+  describe('when query explicitly sets a spec', () => {
+    it('preserves spec display fields from the base', () => {
+      const querySettings = { spec: 'other-spec' } as TPreset;
+
+      const result = mergeQuerySettingsWithSpec(specPreset, querySettings);
+
+      expect(result.spec).toBe('other-spec');
+      expect(result.iconURL).toBe('https://example.com/icon.png');
+      expect(result.modelLabel).toBe('My Custom GPT');
+      expect(result.greeting).toBe('Hello from the spec!');
+    });
+  });
+
+  describe('when specPreset is undefined (no spec configured)', () => {
+    it('returns querySettings without injecting null display fields', () => {
+      const querySettings: TPreset = {
+        agent_id: 'agent_123',
+        endpoint: EModelEndpoint.agents,
+      };
+
+      const result = mergeQuerySettingsWithSpec(undefined, querySettings);
+
+      expect(result.agent_id).toBe('agent_123');
+      expect(result.endpoint).toBe(EModelEndpoint.agents);
+      expect(result).not.toHaveProperty('spec');
+      expect(result).not.toHaveProperty('iconURL');
+      expect(result).not.toHaveProperty('modelLabel');
+      expect(result).not.toHaveProperty('greeting');
+    });
+  });
+
+  describe('when querySettings is empty', () => {
+    it('still clears spec display fields (no query params is not an explicit spec)', () => {
+      const result = mergeQuerySettingsWithSpec(specPreset, {} as TPreset);
+
+      expect(result.spec).toBeNull();
+      expect(result.iconURL).toBeNull();
+      expect(result.modelLabel).toBeNull();
+      expect(result.greeting).toBeUndefined();
+      expect(result.endpoint).toBe(EModelEndpoint.openAI);
+      expect(result.model).toBe('gpt-4');
+      expect(result.temperature).toBe(0.7);
+    });
+  });
+
+  describe('query settings override spec values', () => {
+    it('overrides endpoint and model from spec', () => {
+      const querySettings: TPreset = {
+        endpoint: EModelEndpoint.anthropic,
+        model: 'claude-sonnet-4-20250514',
+      };
+
+      const result = mergeQuerySettingsWithSpec(specPreset, querySettings);
+
+      expect(result.endpoint).toBe(EModelEndpoint.anthropic);
+      expect(result.model).toBe('claude-sonnet-4-20250514');
+      expect(result.temperature).toBe(0.7);
+      expect(result.spec).toBeNull();
+    });
+  });
+});
+
+describe('specDisplayFieldReset', () => {
+  it('contains all spec display fields that need clearing', () => {
+    expect(specDisplayFieldReset).toEqual({
+      spec: null,
+      iconURL: null,
+      modelLabel: null,
+      greeting: undefined,
+    });
+  });
+
+  it('has exactly 4 fields', () => {
+    expect(Object.keys(specDisplayFieldReset)).toHaveLength(4);
+  });
+});