perf(pi-ai): add cache_control breakpoints to tool definitions

Tool definitions are large and static across turns but had no cache
breakpoint. Add a 3rd breakpoint (system → tools → last user message)
for Anthropic direct, Bedrock, and OpenRouter Anthropic providers.

Closes gsd-build/gsd-2#3176

packages/pi-ai/src/providers/amazon-bedrock.ts

@@ -151,7 +151,7 @@ export const streamBedrock: StreamFunction<"bedrock-converse-stream", BedrockOpt
 				messages: convertMessages(context, model, cacheRetention),
 				system: buildSystemPrompt(context.systemPrompt, model, cacheRetention),
 				inferenceConfig: { maxTokens: options.maxTokens, temperature: options.temperature },
-				toolConfig: convertToolConfig(context.tools, options.toolChoice),
+				toolConfig: convertToolConfig(context.tools, options.toolChoice, model, cacheRetention),
 				additionalModelRequestFields: buildAdditionalModelRequestFields(model, options),
 			};
 			const nextCommandInput = await options?.onPayload?.(commandInput, model);
@@ -633,6 +633,8 @@ function convertMessages(
 function convertToolConfig(
 	tools: Tool[] | undefined,
 	toolChoice: BedrockOptions["toolChoice"],
+	model: Model<"bedrock-converse-stream">,
+	cacheRetention: CacheRetention,
 ): ToolConfiguration | undefined {
 	if (!tools?.length || toolChoice === "none") return undefined;
 
@@ -644,6 +646,16 @@ function convertToolConfig(
 		},
 	}));
 
+	// Add cachePoint after last tool for supported models
+	if (cacheRetention !== "none" && supportsPromptCaching(model)) {
+		bedrockTools.push({
+			cachePoint: {
+				type: CachePointType.DEFAULT,
+				...(cacheRetention === "long" ? { ttl: CacheTTL.ONE_HOUR } : {}),
+			},
+		} as any);
+	}
+
 	let bedrockToolChoice: ToolChoice | undefined;
 	switch (toolChoice) {
 		case "auto":

packages/pi-ai/src/providers/anthropic-shared.ts

@@ -393,10 +393,14 @@ export function convertMessages(
 	return params;
 }
 
-export function convertTools(tools: Tool[], isOAuthToken: boolean): Anthropic.Messages.Tool[] {
+export function convertTools(
+	tools: Tool[],
+	isOAuthToken: boolean,
+	cacheControl?: { type: "ephemeral"; ttl?: "1h" },
+): Anthropic.Messages.Tool[] {
 	if (!tools) return [];
 
-	return tools.map((tool) => {
+	const result = tools.map((tool) => {
 		const jsonSchema = tool.parameters as any;
 
 		return {
@@ -409,6 +413,13 @@ export function convertTools(tools: Tool[], isOAuthToken: boolean): Anthropic.Me
 			},
 		};
 	});
+
+	// Add cache breakpoint to last tool — covers entire tool block
+	if (cacheControl && result.length > 0) {
+		(result[result.length - 1] as any).cache_control = cacheControl;
+	}
+
+	return result;
 }
 
 export function buildParams(
@@ -456,7 +467,7 @@ export function buildParams(
 	}
 
 	if (context.tools) {
-		params.tools = convertTools(context.tools, isOAuthToken);
+		params.tools = convertTools(context.tools, isOAuthToken, cacheControl);
 	}
 
 	if (options?.thinkingEnabled && model.reasoning) {

packages/pi-ai/src/providers/openai-completions.ts

@@ -343,6 +343,7 @@ function buildParams(model: Model<"openai-completions">, context: Context, optio
 
 	if (context.tools) {
 		params.tools = convertTools(context.tools, compat);
+		maybeAddOpenRouterAnthropicToolCacheControl(model, params.tools);
 	} else if (hasToolHistory(context.messages)) {
 		// Anthropic (via LiteLLM/proxy) requires tools param when conversation has tool_calls/tool_results
 		params.tools = [];
@@ -379,6 +380,19 @@ function buildParams(model: Model<"openai-completions">, context: Context, optio
 	return params;
 }
 
+function maybeAddOpenRouterAnthropicToolCacheControl(
+	model: Model<"openai-completions">,
+	tools: OpenAI.Chat.Completions.ChatCompletionTool[] | undefined,
+): void {
+	if (model.provider !== "openrouter" || !model.id.startsWith("anthropic/")) return;
+	if (!tools?.length) return;
+
+	const lastTool = tools[tools.length - 1];
+	if ("function" in lastTool) {
+		Object.assign(lastTool.function, { cache_control: { type: "ephemeral" } });
+	}
+}
+
 function mapReasoningEffort(
 	effort: NonNullable<OpenAICompletionsOptions["reasoningEffort"]>,
 	reasoningEffortMap: Partial<Record<NonNullable<OpenAICompletionsOptions["reasoningEffort"]>, string>>,