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Emit usage updates from Claude stream events #506

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e656cc4
Emit usage updates from Claude stream events
Mng-dev-ai Apr 5, 2026
993d8eb
Add stream-event usage update tests
Mng-dev-ai Apr 5, 2026
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81 changes: 76 additions & 5 deletions src/acp-agent.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -109,6 +109,20 @@ type AccumulatedUsage = {
cachedWriteTokens: number;
};

type UsageSnapshot = {
input_tokens: number;
output_tokens: number;
cache_read_input_tokens: number;
cache_creation_input_tokens: number;
};

const ZERO_USAGE: UsageSnapshot = {
input_tokens: 0,
output_tokens: 0,
cache_read_input_tokens: 0,
cache_creation_input_tokens: 0,
};

type Session = {
query: Query;
input: Pushable<SDKUserMessage>;
Expand Down Expand Up @@ -488,6 +502,7 @@ export class ClaudeAcpAgent implements Agent {
};

let lastAssistantTotalUsage: number | null = null;
let lastAssistantUsage: UsageSnapshot | null = null;
let lastAssistantModel: string | null = null;
let lastContextWindowSize: number = 200000;

Expand Down Expand Up @@ -704,6 +719,51 @@ export class ClaudeAcpAgent implements Agent {
break;
}
case "stream_event": {
if (message.parent_tool_use_id === null) {
if (message.event.type === "message_start") {
const usage = message.event.message.usage;
lastAssistantUsage = usage
? {
input_tokens: usage.input_tokens ?? 0,
output_tokens: usage.output_tokens ?? 0,
cache_read_input_tokens: usage.cache_read_input_tokens ?? 0,
cache_creation_input_tokens: usage.cache_creation_input_tokens ?? 0,
}
: null;
if (
message.event.message.model &&
message.event.message.model !== "<synthetic>"
) {
lastAssistantModel = message.event.message.model;
}
} else if (message.event.type === "message_delta") {
const usage = message.event.usage as Partial<UsageSnapshot> | undefined;
if (usage) {
const prev: UsageSnapshot = lastAssistantUsage ?? ZERO_USAGE;
lastAssistantUsage = {
input_tokens: usage.input_tokens ?? prev.input_tokens,
output_tokens: usage.output_tokens ?? prev.output_tokens,
cache_read_input_tokens:
usage.cache_read_input_tokens ?? prev.cache_read_input_tokens,
cache_creation_input_tokens:
usage.cache_creation_input_tokens ?? prev.cache_creation_input_tokens,
};
}
}

const nextUsage = lastAssistantUsage ? totalTokens(lastAssistantUsage) : null;
if (nextUsage !== null && nextUsage !== lastAssistantTotalUsage) {
lastAssistantTotalUsage = nextUsage;
await this.client.sessionUpdate({
sessionId: params.sessionId,
update: {
sessionUpdate: "usage_update",
used: nextUsage,
size: lastContextWindowSize,
},
});
}
}
for (const notification of streamEventToAcpNotifications(
message,
params.sessionId,
Expand Down Expand Up @@ -754,11 +814,13 @@ export class ClaudeAcpAgent implements Agent {
// all four fields is not double-counting.
if ((message.message as any).usage && message.parent_tool_use_id === null) {
const messageWithUsage = message.message as unknown as SDKResultMessage;
lastAssistantTotalUsage =
messageWithUsage.usage.input_tokens +
messageWithUsage.usage.output_tokens +
messageWithUsage.usage.cache_read_input_tokens +
messageWithUsage.usage.cache_creation_input_tokens;
lastAssistantUsage = {
input_tokens: messageWithUsage.usage.input_tokens,
output_tokens: messageWithUsage.usage.output_tokens,
cache_read_input_tokens: messageWithUsage.usage.cache_read_input_tokens,
cache_creation_input_tokens: messageWithUsage.usage.cache_creation_input_tokens,
};
lastAssistantTotalUsage = totalTokens(lastAssistantUsage);
}
// Track the current top-level model for context window size lookup
// (exclude subagent messages to stay in sync with lastAssistantTotalUsage)
Expand Down Expand Up @@ -1569,6 +1631,15 @@ function sessionUsage(session: Session) {
};
}

function totalTokens(usage: UsageSnapshot): number {
return (
usage.input_tokens +
usage.output_tokens +
usage.cache_read_input_tokens +
usage.cache_creation_input_tokens
);
}

function createEnvForGateway(gatewayMeta?: GatewayAuthMeta) {
if (!gatewayMeta) {
return {};
Expand Down
139 changes: 139 additions & 0 deletions src/tests/acp-agent.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1676,6 +1676,23 @@ describe("usage_update computation", () => {
};
}

function createStreamEvent(
eventType: "message_start" | "message_delta",
payload: Record<string, unknown>,
parentToolUseId: string | null = null,
) {
return {
type: "stream_event" as const,
parent_tool_use_id: parentToolUseId,
uuid: randomUUID(),
session_id: "test-session",
event:
eventType === "message_start"
? { type: "message_start" as const, message: payload }
: { type: "message_delta" as const, ...payload },
};
}

function createMockAgentWithCapture() {
const updates: any[] = [];
const mockClient = {
Expand Down Expand Up @@ -1770,6 +1787,128 @@ describe("usage_update computation", () => {
expect(usageUpdate.update.used).toBe(1800);
});

it("stream_event message_start emits usage_update before result", async () => {
const { agent, updates } = createMockAgentWithCapture();
injectSession(agent, [
createStreamEvent("message_start", {
model: "claude-opus-4-20250514",
usage: {
input_tokens: 1000,
output_tokens: 500,
cache_read_input_tokens: 200,
cache_creation_input_tokens: 100,
},
}),
createResultMessageWithModel({
modelUsage: {
"claude-opus-4-20250514": {
inputTokens: 1000,
outputTokens: 500,
cacheReadInputTokens: 200,
cacheCreationInputTokens: 100,
webSearchRequests: 0,
costUSD: 0.01,
contextWindow: 1000000,
maxOutputTokens: 16384,
},
},
}),
{ type: "system", subtype: "session_state_changed", state: "idle" },
]);

await agent.prompt({ sessionId: "test-session", prompt: [{ type: "text", text: "test" }] });

const usageUpdates = updates.filter((u: any) => u.update?.sessionUpdate === "usage_update");
expect(usageUpdates).toHaveLength(2);
expect(usageUpdates[0].update.used).toBe(1800);
expect(usageUpdates[0].update.cost).toBeUndefined();
expect(usageUpdates[1].update.used).toBe(1800);
expect(usageUpdates[1].update.cost).toBeDefined();
});

it("stream_event message_delta patches previous snapshot", async () => {
const { agent, updates } = createMockAgentWithCapture();
injectSession(agent, [
createStreamEvent("message_start", {
model: "claude-opus-4-20250514",
usage: {
input_tokens: 1000,
output_tokens: 0,
cache_read_input_tokens: 200,
cache_creation_input_tokens: 100,
},
}),
createStreamEvent("message_delta", {
usage: { output_tokens: 500 },
}),
createResultMessageWithModel({
modelUsage: {
"claude-opus-4-20250514": {
inputTokens: 1000,
outputTokens: 500,
cacheReadInputTokens: 200,
cacheCreationInputTokens: 100,
webSearchRequests: 0,
costUSD: 0.01,
contextWindow: 1000000,
maxOutputTokens: 16384,
},
},
}),
{ type: "system", subtype: "session_state_changed", state: "idle" },
]);

await agent.prompt({ sessionId: "test-session", prompt: [{ type: "text", text: "test" }] });

const usageUpdates = updates.filter((u: any) => u.update?.sessionUpdate === "usage_update");
expect(usageUpdates).toHaveLength(3);
expect(usageUpdates[0].update.used).toBe(1300);
expect(usageUpdates[0].update.cost).toBeUndefined();
expect(usageUpdates[1].update.used).toBe(1800);
expect(usageUpdates[1].update.cost).toBeUndefined();
expect(usageUpdates[2].update.used).toBe(1800);
expect(usageUpdates[2].update.cost).toBeDefined();
});

it("subagent stream_event does not emit usage_update", async () => {
const { agent, updates } = createMockAgentWithCapture();
injectSession(agent, [
createStreamEvent(
"message_start",
{
model: "claude-haiku-4-5-20251001",
usage: {
input_tokens: 500,
output_tokens: 100,
cache_read_input_tokens: 0,
cache_creation_input_tokens: 0,
},
},
"tool_use_123",
),
createResultMessageWithModel({
modelUsage: {
"claude-haiku-4-5-20251001": {
inputTokens: 500,
outputTokens: 100,
cacheReadInputTokens: 0,
cacheCreationInputTokens: 0,
webSearchRequests: 0,
costUSD: 0.001,
contextWindow: 200000,
maxOutputTokens: 8192,
},
},
}),
{ type: "system", subtype: "session_state_changed", state: "idle" },
]);

await agent.prompt({ sessionId: "test-session", prompt: [{ type: "text", text: "test" }] });

const usageUpdates = updates.filter((u: any) => u.update?.sessionUpdate === "usage_update");
expect(usageUpdates).toHaveLength(0);
});

it("size reflects the current model's context window, not min across all", async () => {
const { agent, updates } = createMockAgentWithCapture();
injectSession(agent, [
Expand Down