fix: omit temperature for claude fable 5 (#9540)

frontend/src/lib/components/copilot/lib.test.ts

@@ -21,6 +21,13 @@ type AssistantMessageWithReasoning = ChatCompletionMessageParam & {
 }
 
 describe('modelConfig', () => {
+	it('flags Fable 5 model IDs via includes matching', () => {
+		expect(modelDisallowsSamplingParams('claude-fable-5')).toBe(true)
+		expect(modelDisallowsSamplingParams('claude-fable-5@20260611')).toBe(true)
+		expect(modelDisallowsSamplingParams('claude-fable-5/thinking')).toBe(true)
+		expect(modelDisallowsSamplingParams('anthropic/claude-fable-5')).toBe(true)
+	})
+
 	it('flags Opus 4.7 model IDs via includes matching', () => {
 		expect(modelDisallowsSamplingParams('claude-opus-4-7')).toBe(true)
 		expect(modelDisallowsSamplingParams('claude-opus-4-7@20260416')).toBe(true)
@@ -41,6 +48,12 @@ describe('modelConfig', () => {
 		).toBeUndefined()
 	})
 
+	it('omits deterministic temperature for Anthropic Fable 5 chat requests', () => {
+		expect(
+			getDefaultChatTemperature({ provider: 'anthropic', model: 'claude-fable-5' })
+		).toBeUndefined()
+	})
+
 	it('omits deterministic temperature for non-anthropic providers carrying Opus 4.7 models', () => {
 		expect(
 			getDefaultChatTemperature({ provider: 'openrouter', model: 'anthropic/claude-opus-4-7' })

frontend/src/lib/components/copilot/modelConfig.ts

@@ -11,6 +11,7 @@ export function modelDisallowsSamplingParams(model: string) {
 	// The o-series match requires a digit after the "o" (o1/o3/o4-mini) so it
 	// does not catch unrelated ids like Mistral's "open-mistral-*" or "optimus-*".
 	return (
+		normalizedModel.includes('claude-fable-5') ||
 		normalizedModel.includes('claude-opus-4-7') ||
 		normalizedModel.includes('claude-opus-4-8') ||
 		baseModel.startsWith('gpt-5') ||