add usage info to branch summary, compaction and tool result entries (#6671)

* add usage info to branch summary entries

* add usage to compaction entries

* allow custom tools to report llm usage in tool results

* allow observing and patching usage in tool_result hooks

* agent-harness: save usage in entries

for compaction, branch summaries and tool results

packages/agent/test/agent-loop.test.ts

@@ -239,6 +239,23 @@ describe("agentLoop with AgentMessage", () => {
 	it("should handle tool calls and results", async () => {
 		const toolSchema = Type.Object({ value: Type.String() });
 		const executed: string[] = [];
+		const toolUsage = {
+			input: 1,
+			output: 2,
+			cacheRead: 3,
+			cacheWrite: 4,
+			totalTokens: 10,
+			cost: { input: 0.1, output: 0.2, cacheRead: 0.3, cacheWrite: 0.4, total: 1 },
+		};
+		const patchedToolUsage = {
+			input: 5,
+			output: 6,
+			cacheRead: 7,
+			cacheWrite: 8,
+			totalTokens: 26,
+			cost: { input: 0.5, output: 0.6, cacheRead: 0.7, cacheWrite: 0.8, total: 2.6 },
+		};
+		let observedToolUsage: typeof toolUsage | undefined;
 		const tool: AgentTool<typeof toolSchema, { value: string }> = {
 			name: "echo",
 			label: "Echo",
@@ -249,6 +266,7 @@ describe("agentLoop with AgentMessage", () => {
 				return {
 					content: [{ type: "text", text: `echoed: ${params.value}` }],
 					details: { value: params.value },
+					usage: toolUsage,
 				};
 			},
 		};
@@ -264,6 +282,10 @@ describe("agentLoop with AgentMessage", () => {
 		const config: AgentLoopConfig = {
 			model: createModel(),
 			convertToLlm: identityConverter,
+			afterToolCall: async ({ result }) => {
+				observedToolUsage = result.usage;
+				return { usage: patchedToolUsage };
+			},
 		};
 
 		let callIndex = 0;
@@ -305,6 +327,10 @@ describe("agentLoop with AgentMessage", () => {
 		if (toolEnd?.type === "tool_execution_end") {
 			expect(toolEnd.isError).toBe(false);
 		}
+		expect(observedToolUsage).toEqual(toolUsage);
+		const messages = await stream.result();
+		const toolResult = messages.find((message) => message.role === "toolResult");
+		expect(toolResult?.role === "toolResult" ? toolResult.usage : undefined).toEqual(patchedToolUsage);
 	});
 
 	it("should not execute tool calls from a length-truncated assistant message", async () => {