fix(ai): require OpenAI Responses terminal events

packages/coding-agent/test/agent-session-stats.test.ts

@@ -140,4 +140,28 @@ describe("AgentSession.getSessionStats", () => {
 			session.dispose();
 		}
 	});
+
+	it("ignores zero-usage messages when checking for post-compaction context usage", () => {
+		const { session, sessionManager } = createSession();
+
+		try {
+			sessionManager.appendMessage(createUserMessage("first", 1));
+			sessionManager.appendMessage(createAssistantMessage("response1", 180_000, 2));
+			const keptUserId = sessionManager.appendMessage(createUserMessage("second", 3));
+			sessionManager.appendMessage(createAssistantMessage("response2", 195_000, 4));
+			sessionManager.appendCompaction("summary", keptUserId, 195_000);
+			sessionManager.appendMessage(createUserMessage("third", 5));
+			sessionManager.appendMessage(createAssistantMessage("response3", 25_000, 6));
+			sessionManager.appendMessage(createUserMessage("continue", 7));
+			sessionManager.appendMessage(createAssistantMessage("partial", 0, 8));
+			syncAgentMessages(session, sessionManager);
+
+			const stats = session.getSessionStats();
+			expect(stats.contextUsage).toBeDefined();
+			expect(stats.contextUsage?.tokens).not.toBeNull();
+			expect(stats.contextUsage?.tokens ?? 0).toBeGreaterThan(25_000);
+		} finally {
+			session.dispose();
+		}
+	});
 });

packages/coding-agent/test/compaction.test.ts

@@ -9,6 +9,7 @@ import {
 	calculateContextTokens,
 	compact,
 	DEFAULT_COMPACTION_SETTINGS,
+	estimateContextTokens,
 	findCutPoint,
 	getLastAssistantUsage,
 	prepareCompaction,
@@ -217,12 +218,43 @@ describe("getLastAssistantUsage", () => {
 		expect(usage!.input).toBe(100);
 	});
 
+	it("should skip all-zero assistant usage", () => {
+		const entries: SessionEntry[] = [
+			createMessageEntry(createUserMessage("Hello")),
+			createMessageEntry(createAssistantMessage("Hi", createMockUsage(100, 50))),
+			createMessageEntry(createUserMessage("continue")),
+			createMessageEntry(createAssistantMessage("Partial", createMockUsage(0, 0))),
+		];
+
+		const usage = getLastAssistantUsage(entries);
+		expect(usage).not.toBeNull();
+		expect(usage!.input).toBe(100);
+	});
+
 	it("should return undefined if no assistant messages", () => {
 		const entries: SessionEntry[] = [createMessageEntry(createUserMessage("Hello"))];
 		expect(getLastAssistantUsage(entries)).toBeUndefined();
 	});
 });
 
+describe("estimateContextTokens", () => {
+	it("uses the last non-zero assistant usage as the context anchor", () => {
+		const messages: AgentMessage[] = [
+			createUserMessage("Hello"),
+			createAssistantMessage("Hi", createMockUsage(100, 50)),
+			createUserMessage("continue"),
+			createAssistantMessage("Partial thinking", createMockUsage(0, 0)),
+		];
+
+		const estimate = estimateContextTokens(messages);
+
+		expect(estimate.usageTokens).toBe(150);
+		expect(estimate.lastUsageIndex).toBe(1);
+		expect(estimate.trailingTokens).toBeGreaterThan(0);
+		expect(estimate.tokens).toBe(150 + estimate.trailingTokens);
+	});
+});
+
 describe("shouldCompact", () => {
 	it("should return true when context exceeds threshold", () => {
 		const settings: CompactionSettings = {