diff --git a/extensions/copilot/src/extension/byok/common/geminiFunctionDeclarationConverter.ts b/extensions/copilot/src/extension/byok/common/geminiFunctionDeclarationConverter.ts
index f25e50d3ee5..990537ed9a0 100644
--- a/extensions/copilot/src/extension/byok/common/geminiFunctionDeclarationConverter.ts
+++ b/extensions/copilot/src/extension/byok/common/geminiFunctionDeclarationConverter.ts
@@ -11,7 +11,7 @@ export type ToolJsonSchema = {
 	properties?: Record<string, ToolJsonSchema>;
 	items?: ToolJsonSchema;
 	required?: string[];
-	enum?: string[];
+	enum?: unknown[];
 
 	// Add support for JSON Schema composition keywords
 	anyOf?: ToolJsonSchema[];
@@ -104,8 +104,11 @@ function transformConcrete(schema: ToolJsonSchema): Schema {
 		transformed.description = schema.description;
 	}
 
-	if (schema.enum) {
-		transformed.enum = schema.enum;
+	if (type === 'string' && schema.enum) {
+		const values = schema.enum.filter((value): value is string => typeof value === 'string');
+		if (values.length > 0) {
+			transformed.enum = values;
+		}
 	}
 
 	if (type === 'object' && schema.properties) {
diff --git a/extensions/copilot/src/extension/byok/common/geminiMessageConverter.ts b/extensions/copilot/src/extension/byok/common/geminiMessageConverter.ts
index 2a8179c1a95..56b0db40d46 100644
--- a/extensions/copilot/src/extension/byok/common/geminiMessageConverter.ts
+++ b/extensions/copilot/src/extension/byok/common/geminiMessageConverter.ts
@@ -4,7 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 import type { Content, FunctionCall, FunctionResponse, Part } from '@google/genai';
 import { Raw } from '@vscode/prompt-tsx';
-import type { LanguageModelChatMessage } from 'vscode';
+import type { LanguageModelChatMessage, LanguageModelChatMessage2 } from 'vscode';
 import { CustomDataPartMimeTypes } from '../../../platform/endpoint/common/endpointTypes';
 import { LanguageModelChatMessageRole, LanguageModelDataPart, LanguageModelTextPart, LanguageModelThinkingPart, LanguageModelToolCallPart, LanguageModelToolResultPart, LanguageModelToolResultPart2 } from '../../../vscodeTypes';
 
@@ -120,7 +120,7 @@ function apiContentToGeminiContent(content: (LanguageModelTextPart | LanguageMod
 	return convertedContent;
 }
 
-export function apiMessageToGeminiMessage(messages: LanguageModelChatMessage[]): { contents: Content[]; systemInstruction?: Content } {
+export function apiMessageToGeminiMessage(messages: Array<LanguageModelChatMessage | LanguageModelChatMessage2>): { contents: Content[]; systemInstruction?: Content } {
 	const contents: Content[] = [];
 	let systemInstruction: Content | undefined;
 
@@ -131,8 +131,7 @@ export function apiMessageToGeminiMessage(messages: LanguageModelChatMessage[]):
 		if (message.role === LanguageModelChatMessageRole.System) {
 			// Gemini uses system instruction separately
 			const systemText = message.content
-				.filter((p): p is LanguageModelTextPart => p instanceof LanguageModelTextPart)
-				.map(p => p.value)
+				.map(part => part instanceof LanguageModelTextPart ? part.value : '')
 				.join('');
 
 			if (systemText.trim()) {
diff --git a/extensions/copilot/src/extension/byok/common/test/geminiFunctionDeclarationConverter.spec.ts b/extensions/copilot/src/extension/byok/common/test/geminiFunctionDeclarationConverter.spec.ts
index 986c6a51749..80b64f6d4d2 100644
--- a/extensions/copilot/src/extension/byok/common/test/geminiFunctionDeclarationConverter.spec.ts
+++ b/extensions/copilot/src/extension/byok/common/test/geminiFunctionDeclarationConverter.spec.ts
@@ -179,6 +179,41 @@ describe('GeminiFunctionDeclarationConverter', () => {
 			});
 		});
 
+		it('should omit non-string enums from nested schemas', () => {
+			const result = toGeminiFunction('nestedEnumFunction', 'Function with nested non-string enums', {
+				type: 'object',
+				properties: {
+					values: {
+						type: 'array',
+						items: {
+							type: 'object',
+							properties: {
+								enabled: {
+									type: 'boolean',
+									enum: [true]
+								},
+								count: {
+									type: 'integer',
+									enum: [1, 2]
+								}
+							}
+						}
+					}
+				}
+			});
+
+			expect(result.parameters!.properties!['values']).toEqual({
+				type: Type.ARRAY,
+				items: {
+					type: Type.OBJECT,
+					properties: {
+						enabled: { type: Type.BOOLEAN },
+						count: { type: Type.INTEGER }
+					}
+				}
+			});
+		});
+
 		it('should handle nullable anyOf schemas', () => {
 			const result = toGeminiFunction('nullableAnyOfFunction', 'Function with nullable anyOf', {
 				type: 'object',
diff --git a/extensions/copilot/src/extension/byok/common/test/geminiMessageConverter.spec.ts b/extensions/copilot/src/extension/byok/common/test/geminiMessageConverter.spec.ts
index 68e36160eb4..1d02c638f2e 100644
--- a/extensions/copilot/src/extension/byok/common/test/geminiMessageConverter.spec.ts
+++ b/extensions/copilot/src/extension/byok/common/test/geminiMessageConverter.spec.ts
@@ -5,9 +5,9 @@
 
 import { Raw } from '@vscode/prompt-tsx';
 import { describe, expect, it } from 'vitest';
-import type { LanguageModelChatMessage } from 'vscode';
+import type { LanguageModelChatMessage, LanguageModelChatMessage2 } from 'vscode';
 import { CustomDataPartMimeTypes } from '../../../../platform/endpoint/common/endpointTypes';
-import { LanguageModelChatMessageRole, LanguageModelDataPart, LanguageModelTextPart, LanguageModelToolResultPart, LanguageModelTextPart as LMText } from '../../../../vscodeTypes';
+import { LanguageModelChatMessageRole, LanguageModelDataPart, LanguageModelTextPart, LanguageModelThinkingPart, LanguageModelToolCallPart, LanguageModelToolResultPart, LanguageModelTextPart as LMText } from '../../../../vscodeTypes';
 import { apiMessageToGeminiMessage } from '../geminiMessageConverter';
 
 describe('GeminiMessageConverter', () => {
@@ -80,6 +80,27 @@ describe('GeminiMessageConverter', () => {
 		expect(result.contents[0].parts![1].text).toBe('Hello!');
 	});
 
+	it('should attach a thought signature to the following function call', () => {
+		const messages: Array<LanguageModelChatMessage | LanguageModelChatMessage2> = [{
+			role: LanguageModelChatMessageRole.Assistant,
+			content: [
+				new LanguageModelThinkingPart('', undefined, { signature: 'thought-signature' }),
+				new LanguageModelToolCallPart('call-1', 'default_api:view', { path: 'README.md' }),
+			],
+			name: undefined,
+		}];
+
+		const result = apiMessageToGeminiMessage(messages);
+
+		expect(result.contents[0].parts).toEqual([{
+			functionCall: {
+				name: 'default_api:view',
+				args: { path: 'README.md' },
+			},
+			thoughtSignature: 'thought-signature',
+		}]);
+	});
+
 	it('should extract functionResponse parts from model message into subsequent user message and prune empty model', () => {
 		// Simulate a model message that (incorrectly) contains only a tool result part
 		const toolResult = new LanguageModelToolResultPart('myTool_12345', [new LanguageModelTextPart('{"foo":"bar"}')]);