fix: complete extension usage accounting

closes #6509

packages/agent/CHANGELOG.md

@@ -6,6 +6,10 @@
 
 - Moved the `uuidv7` export to `@earendil-works/pi-ai`.
 
+### Added
+
+- Added usage metadata to tool results, compaction entries, and branch summaries in the agent harness ([#6671](https://github.com/earendil-works/pi/pull/6671) by [@davidbrai](https://github.com/davidbrai)).
+
 ## [0.80.10] - 2026-07-16
 
 ## [0.80.9] - 2026-07-16

packages/agent/src/harness/compaction/compaction.ts

@@ -499,6 +499,30 @@ export async function generateSummary(
 	customInstructions?: string,
 	previousSummary?: string,
 	thinkingLevel?: ThinkingLevel,
+): Promise<Result<string, CompactionError>> {
+	const result = await generateSummaryWithUsage(
+		currentMessages,
+		models,
+		model,
+		reserveTokens,
+		signal,
+		customInstructions,
+		previousSummary,
+		thinkingLevel,
+	);
+	return result.ok ? ok(result.value.text) : err(result.error);
+}
+
+/** Generate or update a conversation summary and return its provider usage. */
+export async function generateSummaryWithUsage(
+	currentMessages: AgentMessage[],
+	models: Models,
+	model: Model<any>,
+	reserveTokens: number,
+	signal?: AbortSignal,
+	customInstructions?: string,
+	previousSummary?: string,
+	thinkingLevel?: ThinkingLevel,
 ): Promise<Result<{ text: string; usage: Usage }, CompactionError>> {
 	const maxTokens = Math.min(
 		Math.floor(0.8 * reserveTokens),
@@ -687,7 +711,7 @@ export async function compact(
 		let historyText = "No prior history.";
 		let historyUsage: Usage | undefined;
 		if (messagesToSummarize.length > 0) {
-			const historyResult = await generateSummary(
+			const historyResult = await generateSummaryWithUsage(
 				messagesToSummarize,
 				models,
 				model,
@@ -715,7 +739,7 @@ export async function compact(
 			? combineUsage(historyUsage, turnPrefixResult.value.usage)
 			: turnPrefixResult.value.usage;
 	} else {
-		const summaryResult = await generateSummary(
+		const summaryResult = await generateSummaryWithUsage(
 			messagesToSummarize,
 			models,
 			model,

packages/agent/src/index.ts

@@ -20,6 +20,7 @@ export {
 	findCutPoint,
 	findTurnStartIndex,
 	generateSummary,
+	generateSummaryWithUsage,
 	getLastAssistantUsage,
 	prepareCompaction,
 	serializeConversation,

packages/agent/test/harness/compaction.test.ts

@@ -20,6 +20,7 @@ import {
 	findCutPoint,
 	findTurnStartIndex,
 	generateSummary,
+	generateSummaryWithUsage,
 	getLastAssistantUsage,
 	prepareCompaction,
 	serializeConversation,
@@ -510,7 +511,7 @@ describe("harness compaction", () => {
 		]);
 
 		const summary = getOrThrow(
-			await generateSummary(messages, models, model, 2000, undefined, "focus", "old summary"),
+			await generateSummaryWithUsage(messages, models, model, 2000, undefined, "focus", "old summary"),
 		);
 
 		expect(summary.text).toContain("Test summary");
@@ -523,6 +524,14 @@ describe("harness compaction", () => {
 		expect(promptText).toContain("Additional focus: focus");
 	});
 
+	it("preserves the string result from generateSummary", async () => {
+		const messages: AgentMessage[] = [createUserMessage("Summarize this.")];
+		const { faux, model } = createFauxModel(false);
+		faux.setResponses([fauxAssistantMessage("## Goal\nTest summary")]);
+
+		expect(getOrThrow(await generateSummary(messages, models, model, 2000))).toBe("## Goal\nTest summary");
+	});
+
 	it("returns error results for failed or aborted summary generations", async () => {
 		const messages: AgentMessage[] = [createUserMessage("Summarize this.")];
 		const { faux: errorFaux, model: errorModel } = createFauxModel(false);