fix: read token usage from ACP response instead of DB

Tokens (inputTokens, outputTokens) now come from ACP PromptResponse.usage
which is populated synchronously from run_conversation() — no WAL race.
Turns still come from DB before/after snapshot.

Previously both were read from hermes state.db after ACP prompt returned,
but WAL write lag caused incomplete token data (e.g. 235 vs actual 26,080).

Refs #91

packages/agent-hermes/__tests__/usage-delta.test.ts

@@ -1,5 +1,6 @@
 import { describe, expect, test } from "vitest";
-import { computeUsageDelta, snapshotUsage } from "../src/hermes.js";
+import type { AcpUsage } from "../src/acp-client.js";
+import { buildUsage, snapshotTurns } from "../src/hermes.js";
 import type { HermesSessionJson } from "../src/types.js";
 
 function makeSession(overrides: Partial<HermesSessionJson> = {}): HermesSessionJson {
@@ -14,19 +15,19 @@ function makeSession(overrides: Partial<HermesSessionJson> = {}): HermesSessionJ
   };
 }
 
-describe("snapshotUsage", () => {
-  test("returns zero snapshot for null session", () => {
-    const result = snapshotUsage(null);
-    expect(result).toEqual({ turns: 0, inputTokens: 0, outputTokens: 0 });
+describe("snapshotTurns", () => {
+  test("returns zero for null session", () => {
+    const result = snapshotTurns(null);
+    expect(result).toEqual({ turns: 0 });
   });
 
-  test("returns zero snapshot for empty session", () => {
-    const result = snapshotUsage(makeSession());
-    expect(result).toEqual({ turns: 0, inputTokens: 0, outputTokens: 0 });
+  test("returns zero for empty session", () => {
+    const result = snapshotTurns(makeSession());
+    expect(result).toEqual({ turns: 0 });
   });
 
   test("counts assistant messages as turns", () => {
-    const result = snapshotUsage(
+    const result = snapshotTurns(
       makeSession({
         messages: [
           { role: "user", content: "hello", reasoning: null, tool_calls: null },
@@ -39,11 +40,11 @@ describe("snapshotUsage", () => {
         outputTokens: 500,
       }),
     );
-    expect(result).toEqual({ turns: 2, inputTokens: 1000, outputTokens: 500 });
+    expect(result).toEqual({ turns: 2 });
   });
 
   test("ignores non-assistant messages for turn count", () => {
-    const result = snapshotUsage(
+    const result = snapshotTurns(
       makeSession({
         messages: [
           { role: "user", content: "hello", reasoning: null, tool_calls: null },
@@ -55,11 +56,13 @@ describe("snapshotUsage", () => {
   });
 });
 
-describe("computeUsageDelta", () => {
-  test("first visit: before is zero, after has all values", () => {
-    const before = { turns: 0, inputTokens: 0, outputTokens: 0 };
-    const after = { turns: 3, inputTokens: 5000, outputTokens: 2000 };
-    const result = computeUsageDelta(before, after, 12.5);
+describe("buildUsage", () => {
+  const acpUsage: AcpUsage = { inputTokens: 5000, outputTokens: 2000, totalTokens: 7000 };
+
+  test("first visit: tokens from ACP, turns from DB delta", () => {
+    const beforeTurns = { turns: 0 };
+    const afterTurns = { turns: 3 };
+    const result = buildUsage(acpUsage, beforeTurns, afterTurns, 12.5);
     expect(result).toEqual({
       turns: 3,
       inputTokens: 5000,
@@ -68,43 +71,52 @@ describe("computeUsageDelta", () => {
     });
   });
 
-  test("re-entry: computes delta correctly", () => {
-    const before = { turns: 2, inputTokens: 3000, outputTokens: 1000 };
-    const after = { turns: 4, inputTokens: 8000, outputTokens: 3500 };
-    const result = computeUsageDelta(before, after, 7.3);
+  test("re-entry: turn delta computed correctly, tokens from ACP", () => {
+    const beforeTurns = { turns: 2 };
+    const afterTurns = { turns: 4 };
+    const acpDelta: AcpUsage = { inputTokens: 8000, outputTokens: 3500, totalTokens: 11500 };
+    const result = buildUsage(acpDelta, beforeTurns, afterTurns, 7.3);
     expect(result).toEqual({
       turns: 2,
-      inputTokens: 5000,
-      outputTokens: 2500,
+      inputTokens: 8000,
+      outputTokens: 3500,
       duration: 7,
     });
   });
 
-  test("floors negative deltas at 0 (defensive)", () => {
-    const before = { turns: 5, inputTokens: 10000, outputTokens: 5000 };
-    const after = { turns: 3, inputTokens: 8000, outputTokens: 4000 };
-    const result = computeUsageDelta(before, after, 1.0);
+  test("floors negative turn deltas at 0, then defaults to 1", () => {
+    const beforeTurns = { turns: 5 };
+    const afterTurns = { turns: 3 };
+    const result = buildUsage(acpUsage, beforeTurns, afterTurns, 1.0);
     // turns would be negative (-2), floored to 0, then || 1 gives 1
     expect(result.turns).toBe(1);
-    expect(result.inputTokens).toBe(0);
-    expect(result.outputTokens).toBe(0);
   });
 
   test("zero turns delta defaults to 1 (at least one turn happened)", () => {
-    const before = { turns: 3, inputTokens: 1000, outputTokens: 500 };
-    const after = { turns: 3, inputTokens: 2000, outputTokens: 1000 };
-    const result = computeUsageDelta(before, after, 5.0);
+    const beforeTurns = { turns: 3 };
+    const afterTurns = { turns: 3 };
+    const result = buildUsage(acpUsage, beforeTurns, afterTurns, 5.0);
     // turns delta is 0, || 1 gives 1
     expect(result.turns).toBe(1);
-    expect(result.inputTokens).toBe(1000);
-    expect(result.outputTokens).toBe(500);
+  });
+
+  test("null ACP usage yields zero tokens", () => {
+    const beforeTurns = { turns: 0 };
+    const afterTurns = { turns: 2 };
+    const result = buildUsage(null, beforeTurns, afterTurns, 10.0);
+    expect(result).toEqual({
+      turns: 2,
+      inputTokens: 0,
+      outputTokens: 0,
+      duration: 10,
+    });
   });
 
   test("duration is rounded", () => {
-    const before = { turns: 0, inputTokens: 0, outputTokens: 0 };
-    const after = { turns: 1, inputTokens: 100, outputTokens: 50 };
-    expect(computeUsageDelta(before, after, 3.7).duration).toBe(4);
-    expect(computeUsageDelta(before, after, 3.2).duration).toBe(3);
-    expect(computeUsageDelta(before, after, 0.0).duration).toBe(0);
+    const beforeTurns = { turns: 0 };
+    const afterTurns = { turns: 1 };
+    expect(buildUsage(acpUsage, beforeTurns, afterTurns, 3.7).duration).toBe(4);
+    expect(buildUsage(acpUsage, beforeTurns, afterTurns, 3.2).duration).toBe(3);
+    expect(buildUsage(acpUsage, beforeTurns, afterTurns, 0.0).duration).toBe(0);
   });
 });

packages/agent-hermes/src/acp-client.ts

@@ -17,9 +17,17 @@ type PendingRequest = {
   reject: (reason: Error) => void;
 };
 
+/** Token usage returned by ACP PromptResponse. */
+export type AcpUsage = {
+  inputTokens: number;
+  outputTokens: number;
+  totalTokens: number;
+};
+
 export type AcpPromptResult = {
   text: string;
   sessionId: string;
+  usage: AcpUsage | null;
 };
 
 export class HermesAcpClient {
@@ -96,9 +104,25 @@ export class HermesAcpClient {
       );
     }
 
+    // Extract token usage from ACP PromptResponse.result.usage (camelCase wire format)
+    const result = (response as { result?: Record<string, unknown> }).result;
+    const rawUsage = result?.usage as Record<string, unknown> | undefined;
+    const usage: AcpUsage | null =
+      rawUsage !== undefined &&
+      typeof rawUsage.inputTokens === "number" &&
+      typeof rawUsage.outputTokens === "number" &&
+      typeof rawUsage.totalTokens === "number"
+        ? {
+            inputTokens: rawUsage.inputTokens,
+            outputTokens: rawUsage.outputTokens,
+            totalTokens: rawUsage.totalTokens,
+          }
+        : null;
+
     return {
       text: this.messageChunks.join(""),
       sessionId: this.sessionId,
+      usage,
     };
   }
 

packages/agent-hermes/src/hermes.ts

@@ -8,7 +8,7 @@ import {
   buildRolePrompt,
   createAgent,
 } from "@united-workforce/util-agent";
-
+import type { AcpUsage } from "./acp-client.js";
 import { HermesAcpClient } from "./acp-client.js";
 import { getCachedSessionId, setCachedSessionId } from "./session-cache.js";
 import { loadHermesSession, storeHermesSessionDetail } from "./session-detail.js";
@@ -17,36 +17,37 @@ import type { HermesSessionJson } from "./types.js";
 const log = createLogger({ sink: { kind: "stderr" } });
 
 /** Snapshot of session metrics taken before and after a prompt call. */
-type UsageSnapshot = {
+type TurnsSnapshot = {
   turns: number;
-  inputTokens: number;
-  outputTokens: number;
 };
 
-const ZERO_SNAPSHOT: UsageSnapshot = { turns: 0, inputTokens: 0, outputTokens: 0 };
+const ZERO_TURNS: TurnsSnapshot = { turns: 0 };
 
-/** Extract usage metrics from a session. Returns zeros for null sessions. */
-export function snapshotUsage(session: HermesSessionJson | null): UsageSnapshot {
+/** Extract assistant turn count from a session. Returns zero for null sessions. */
+export function snapshotTurns(session: HermesSessionJson | null): TurnsSnapshot {
   if (session === null) {
-    return ZERO_SNAPSHOT;
+    return ZERO_TURNS;
   }
   return {
     turns: session.messages.filter((m) => m.role === "assistant").length,
-    inputTokens: session.inputTokens,
-    outputTokens: session.outputTokens,
   };
 }
 
-/** Compute the delta between two snapshots (after minus before). Floors at 0. */
-export function computeUsageDelta(
-  before: UsageSnapshot,
-  after: UsageSnapshot,
+/**
+ * Build Usage from ACP token data + DB turn delta.
+ * Tokens come from ACP PromptResponse (synchronous, accurate).
+ * Turns come from DB before/after snapshots (may have WAL lag, but acceptable).
+ */
+export function buildUsage(
+  acpUsage: AcpUsage | null,
+  beforeTurns: TurnsSnapshot,
+  afterTurns: TurnsSnapshot,
   durationSec: number,
 ): Usage {
   return {
-    turns: Math.max(0, after.turns - before.turns) || 1,
-    inputTokens: Math.max(0, after.inputTokens - before.inputTokens),
-    outputTokens: Math.max(0, after.outputTokens - before.outputTokens),
+    turns: Math.max(0, afterTurns.turns - beforeTurns.turns) || 1,
+    inputTokens: acpUsage?.inputTokens ?? 0,
+    outputTokens: acpUsage?.outputTokens ?? 0,
     duration: Math.round(durationSec),
   };
 }
@@ -148,12 +149,12 @@ export function createHermesAgent(resumeDisabled: boolean): () => Promise<void>
   async function runPrompt(
     ctx: AgentContext,
     useContinuation: boolean,
-    beforeSnapshot: UsageSnapshot,
+    beforeTurns: TurnsSnapshot,
   ): Promise<AgentRunResult> {
     const effectiveCtx = useContinuation ? ctx : { ...ctx, isFirstVisit: true };
     const fullPrompt = buildHermesPrompt(effectiveCtx);
     const startMs = Date.now();
-    const { text, sessionId } = await client.prompt(fullPrompt);
+    const { text, sessionId, usage: acpUsage } = await client.prompt(fullPrompt);
     const durationSec = (Date.now() - startMs) / 1000;
     const { detailHash } = await storePromptResult(ctx.store, sessionId);
 
@@ -161,9 +162,10 @@ export function createHermesAgent(resumeDisabled: boolean): () => Promise<void>
       await setCachedSessionId(ctx.threadId, ctx.role, sessionId, ctx.storageRoot);
     }
 
+    // Turns from DB (may lag slightly due to WAL, but acceptable)
     const afterSession = await loadHermesSession(sessionId);
-    const afterSnapshot = snapshotUsage(afterSession);
-    const usage = computeUsageDelta(beforeSnapshot, afterSnapshot, durationSec);
+    const afterTurns = snapshotTurns(afterSession);
+    const usage = buildUsage(acpUsage, beforeTurns, afterTurns, durationSec);
 
     return { output: text, detailHash, sessionId, assembledPrompt: fullPrompt, usage };
   }
@@ -173,16 +175,16 @@ export function createHermesAgent(resumeDisabled: boolean): () => Promise<void>
     const attempt = await prepareSession(client, ctx, cwd, resumeDisabled);
 
     // Snapshot before prompt: for resumed sessions, captures cumulative state
-    // so we can compute the delta. For new sessions, this is ZERO_SNAPSHOT.
+    // so we can compute the turn delta. For new sessions, this is ZERO_TURNS.
     const currentSessionId = client.getSessionId();
     const beforeSession =
       attempt.resumed && currentSessionId !== null
         ? await loadHermesSession(currentSessionId)
         : null;
-    const beforeSnapshot = snapshotUsage(beforeSession);
+    const beforeTurns = snapshotTurns(beforeSession);
 
     try {
-      return await runPrompt(ctx, attempt.useContinuation, beforeSnapshot);
+      return await runPrompt(ctx, attempt.useContinuation, beforeTurns);
     } catch (error) {
       if (!attempt.resumed) {
         throw error;
@@ -193,7 +195,7 @@ export function createHermesAgent(resumeDisabled: boolean): () => Promise<void>
       await client.close();
       await client.connect(cwd);
       // Fresh session after retry — reset snapshot to zero
-      return runPrompt(ctx, false, ZERO_SNAPSHOT);
+      return runPrompt(ctx, false, ZERO_TURNS);
     }
   }
 
@@ -204,20 +206,20 @@ export function createHermesAgent(resumeDisabled: boolean): () => Promise<void>
   ): Promise<AgentRunResult> {
     // Client is already connected from runHermes — same ACP session,
     // so the agent sees the full conversation history (crucial for retries).
-    // Snapshot before the continuation prompt for delta computation.
+    // Snapshot turns before the continuation prompt for delta computation.
     const currentSessionId = client.getSessionId();
     const beforeSession =
       currentSessionId !== null ? await loadHermesSession(currentSessionId) : null;
-    const beforeSnapshot = snapshotUsage(beforeSession);
+    const beforeTurns = snapshotTurns(beforeSession);
 
     const startMs = Date.now();
-    const { text, sessionId } = await client.prompt(message);
+    const { text, sessionId, usage: acpUsage } = await client.prompt(message);
     const durationSec = (Date.now() - startMs) / 1000;
     const { detailHash } = await storePromptResult(store, sessionId);
 
     const afterSession = await loadHermesSession(sessionId);
-    const afterSnapshot = snapshotUsage(afterSession);
-    const usage = computeUsageDelta(beforeSnapshot, afterSnapshot, durationSec);
+    const afterTurns = snapshotTurns(afterSession);
+    const usage = buildUsage(acpUsage, beforeTurns, afterTurns, durationSec);
 
     return { output: text, detailHash, sessionId, assembledPrompt: "", usage };
   }

packages/agent-hermes/src/index.ts

@@ -1,7 +1,8 @@
+export type { AcpUsage } from "./acp-client.js";
 export { HermesAcpClient } from "./acp-client.js";
 export {
   buildHermesPrompt,
-  computeUsageDelta,
+  buildUsage,
   createHermesAgent,
-  snapshotUsage,
+  snapshotTurns,
 } from "./hermes.js";