fix(ai): ignore stale usage after compaction

closes #6464
2026-07-09 21:44:01 +02:00
parent 8432c6f285
commit 8973ae28ab
3 changed files with 109 additions and 9 deletions
@@ -0,0 +1,81 @@
+import { describe, expect, it } from "vitest";
+import { buildBaseOptions } from "../src/api/simple-options.ts";
+import type { AssistantMessage, Context, Model, Usage } from "../src/types.ts";
+import { estimateContextTokens } from "../src/utils/estimate.ts";
+
+function createUsage(totalTokens: number): Usage {
+	return {
+		input: totalTokens,
+		output: 0,
+		cacheRead: 0,
+		cacheWrite: 0,
+		totalTokens,
+		cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+	};
+}
+
+function createAssistant(timestamp: number, totalTokens: number): AssistantMessage {
+	return {
+		role: "assistant",
+		content: [{ type: "text", text: "kept" }],
+		api: "openai-responses",
+		provider: "openai",
+		model: "test-model",
+		usage: createUsage(totalTokens),
+		stopReason: "stop",
+		timestamp,
+	};
+}
+
+const model: Model<"openai-responses"> = {
+	id: "test-model",
+	name: "Test Model",
+	api: "openai-responses",
+	provider: "openai",
+	baseUrl: "https://api.openai.com/v1",
+	reasoning: false,
+	input: ["text"],
+	cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+	contextWindow: 10_000,
+	maxTokens: 8_000,
+};
+
+describe("context token estimation", () => {
+	it("ignores stale assistant usage after a newer message is inserted before it", () => {
+		const context: Context = {
+			systemPrompt: "system",
+			messages: [
+				{ role: "user", content: "summary", timestamp: 200 },
+				createAssistant(100, 9_500),
+				{ role: "user", content: "x".repeat(4_000), timestamp: 300 },
+			],
+		};
+
+		expect(estimateContextTokens(context)).toEqual({
+			tokens: 1_005,
+			usageTokens: 0,
+			trailingTokens: 1_005,
+			lastUsageIndex: null,
+		});
+		expect(buildBaseOptions(model, context).maxTokens).toBe(4_899);
+	});
+
+	it("uses assistant usage again after a response to the inserted context", () => {
+		const context: Context = {
+			messages: [
+				{ role: "user", content: "summary", timestamp: 200 },
+				createAssistant(100, 9_500),
+				{ role: "user", content: "new prompt", timestamp: 300 },
+				createAssistant(400, 2_000),
+				{ role: "user", content: "tail", timestamp: 500 },
+			],
+		};
+
+		expect(estimateContextTokens(context)).toEqual({
+			tokens: 2_001,
+			usageTokens: 2_000,
+			trailingTokens: 1,
+			lastUsageIndex: 3,
+		});
+	});
+});