Budget basic compaction projections

sdk/packages/core/src/extensions/context/basic-compaction.ts

@@ -3,6 +3,7 @@ import type {
 	CoreCompactionContext,
 	CoreCompactionResult,
 } from "../../types/config";
+import { buildBudgetProjection } from "./budget-projection";
 import {
 	type EstimateMessageTokens,
 	findFirstUserMessageIndex,
@@ -390,7 +391,23 @@ export function runBasicCompaction(options: {
 		...candidates.map((candidate) => candidate.message),
 		...protectedTail,
 	];
-	if (!haveMessagesChanged(options.context.messages, nextMessages)) {
+	const budgeted = buildBudgetProjection({
+		messages: nextMessages,
+		targetTokens,
+		policyIntent: "basic_compaction_projection",
+		estimateMessageTokens: options.estimateMessageTokens,
+	});
+	if (budgeted.status === "failed") {
+		options.logger?.debug("Basic compaction returned best-effort projection", {
+			budgetWarnings: budgeted.warnings.map((warning) => warning.code),
+			projectedTokens: budgeted.estimatedTokens,
+			targetTokens,
+			maxInputTokens: options.context.maxInputTokens,
+		});
+	}
+	const resultMessages = budgeted.messages;
+
+	if (!haveMessagesChanged(options.context.messages, resultMessages)) {
 		return undefined;
 	}
 
@@ -402,18 +419,20 @@ export function runBasicCompaction(options: {
 		options.estimateMessageTokens,
 	);
 	const afterTokens = getTotalTokens(
-		nextMessages,
+		resultMessages,
 		options.estimateMessageTokens,
 	);
 	options.logger?.debug("Performed basic compaction", {
 		messagesBefore: options.context.messages.length,
-		messagesAfter: nextMessages.length,
-		messagesRemoved: options.context.messages.length - nextMessages.length,
+		messagesAfter: resultMessages.length,
+		messagesRemoved: options.context.messages.length - resultMessages.length,
 		tokensBefore: beforeTokens,
 		tokensAfter: afterTokens,
+		budgetActions: budgeted.actions.length,
+		budgetWarnings: budgeted.warnings.map((warning) => warning.code),
 		targetTokens,
 		maxInputTokens: options.context.maxInputTokens,
 	});
 
-	return { messages: nextMessages };
+	return { messages: resultMessages };
 }

sdk/packages/core/src/extensions/context/compaction.test.ts

@@ -365,13 +365,28 @@ describe("createContextCompactionPrepareTurn", () => {
 		const compacted = runForcedBasicCompaction(messages, 1);
 
 		expect(compacted).toEqual([
-			{ role: "user", content: "Old request" },
 			{ role: "user", content: "Read the latest file" },
 			assistantToolUseMessage("tool-a"),
 			toolResultMessage("tool-a", "latest result"),
 		]);
 	});
 
+	it("budgets the complete basic compaction output including the latest turn", () => {
+		const messages: LlmsProviders.Message[] = [
+			{ role: "user", content: "original task" },
+			{ role: "assistant", content: "old assistant " + "x".repeat(10_000) },
+			{ role: "user", content: "latest typed prompt" },
+			assistantToolUseMessage("tool-live"),
+			toolResultMessage("tool-live", "live result " + "y".repeat(10_000)),
+		];
+
+		const compacted = runForcedBasicCompaction(messages, 700);
+
+		expect(totalJsonTokens(compacted)).toBeLessThanOrEqual(700);
+		expect(JSON.stringify(compacted)).toContain("latest typed prompt");
+		expectNoOrphanedToolPairs(compacted);
+	});
+
 	it("does not compact a single typed user message", () => {
 		const messages: LlmsProviders.Message[] = [
 			{ role: "user", content: "Only current request" },