feat(core): record title and compaction usage in session totals (#37441)

packages/client/src/promise/generated/types.ts

@@ -803,6 +803,16 @@ export type SessionRevertCommitted = {
   data: { sessionID: string; to: string }
 }
 
+export type SessionUsageRecorded = {
+  id: string
+  created: number
+  metadata?: { [x: string]: any }
+  type: "session.usage.recorded"
+  durable: { aggregateID: string; seq: number; version: 1 }
+  location?: LocationRef
+  data: { sessionID: string; source: "title" | "compaction"; cost: MoneyUSD; tokens: TokenUsageInfo }
+}
+
 export type ModelsDevRefreshed = {
   id: string
   created: number
@@ -2216,6 +2226,7 @@ export type SessionEventDurable =
   | SessionRevertStaged
   | SessionRevertCleared
   | SessionRevertCommitted
+  | SessionUsageRecorded
 
 export type SessionMessagesResponse = {
   data: Array<SessionMessageInfo>

packages/core/src/session.ts

@@ -210,12 +210,11 @@ export interface Interface {
    */
   readonly pending: (sessionID: SessionSchema.ID) => Effect.Effect<SessionPending.Info[], NotFoundError>
   /**
-   * Durable, ordered session log read. Replays public durable
-   * session events after the exclusive `after` cursor, emits a `Synced`
-   * marker at the captured replay watermark, then continues live when `follow`
-   * is set.
-   * The marker's seq may exceed the last emitted event because non-public
-   * durable events share the aggregate's sequence space.
+   * Durable, ordered session log read. Replays durable session events after
+   * the exclusive `after` cursor, emits a `Synced` marker at the captured
+   * replay watermark, then continues live when `follow` is set.
+   * The marker's seq may exceed the last emitted event because other durable
+   * events share the aggregate's sequence space.
    */
   readonly log: (input: {
     sessionID: SessionSchema.ID

packages/core/src/session/compaction.ts

@@ -14,6 +14,8 @@ import { SessionRunnerModel } from "./runner/model"
 import { SessionSchema } from "./schema"
 import { toSessionError } from "./to-session-error"
 import { Token } from "../util/token"
+import type { ModelV2 } from "../model"
+import { SessionUsage } from "./usage"
 
 const DEFAULT_BUFFER = 20_000
 const DEFAULT_KEEP_TOKENS = 8_000
@@ -70,6 +72,7 @@ export type AutoInput = {
   readonly session: SessionSchema.Info
   readonly messages: readonly SessionMessage.Info[]
   readonly model: Model
+  readonly cost: ModelV2.Info["cost"]
 }
 
 export type ManualInput = {
@@ -81,6 +84,7 @@ export type ManualInput = {
 type Plan = {
   readonly session: SessionSchema.Info
   readonly model: Model
+  readonly cost: ModelV2.Info["cost"]
   readonly reason: SessionMessage.Compaction["reason"]
   readonly prompt: string
   readonly recent: string
@@ -240,6 +244,16 @@ const make = (dependencies: Dependencies) => {
 
     const chunks: string[] = []
     let failure: SessionError.Error | undefined
+    let usage: SessionUsage.Recorded | undefined
+    const recordUsage = Effect.suspend(() =>
+      usage
+        ? dependencies.events.publish(SessionEvent.UsageRecorded, {
+            sessionID: plan.session.id,
+            source: "compaction",
+            ...usage,
+          })
+        : Effect.void,
+    )
     yield* dependencies.llm
       .stream(
         LLM.request({
@@ -263,6 +277,10 @@ const make = (dependencies: Dependencies) => {
               text: event.text,
             })
           }
+          if (LLMEvent.is.stepFinish(event)) {
+            const step = SessionUsage.record(event.usage, plan.cost)
+            usage = usage ? SessionUsage.add(usage, step) : step
+          }
           return Effect.void
         }),
         Effect.catchTag("LLM.Error", (error) =>
@@ -271,16 +289,21 @@ const make = (dependencies: Dependencies) => {
           }),
         ),
         Effect.onInterrupt(() =>
-          plan.reason === "auto"
-            ? failed({
-                sessionID: plan.session.id,
-                reason: plan.reason,
-                error: { type: "compaction.interrupted", message: "Compaction was interrupted" },
-                inputID: plan.inputID,
-              }).pipe(Effect.asVoid)
-            : Effect.void,
+          recordUsage.pipe(
+            Effect.andThen(
+              plan.reason === "auto"
+                ? failed({
+                    sessionID: plan.session.id,
+                    reason: plan.reason,
+                    error: { type: "compaction.interrupted", message: "Compaction was interrupted" },
+                    inputID: plan.inputID,
+                  }).pipe(Effect.asVoid)
+                : Effect.void,
+            ),
+          ),
         ),
       )
+    yield* recordUsage
     const summary = chunks.join("")
     if (failure || !summary.trim()) {
       const error = failure ?? { type: "compaction.failed" as const, message: "Compaction produced no summary" }
@@ -305,6 +328,7 @@ const make = (dependencies: Dependencies) => {
       return yield* execute({
         session: input.session,
         model: input.model,
+        cost: input.cost,
         reason: "auto",
         ...content,
       })
@@ -353,6 +377,7 @@ const make = (dependencies: Dependencies) => {
     return yield* execute({
       session: input.session,
       model: resolved.model,
+      cost: resolved.cost,
       reason: "manual",
       inputID: input.inputID,
       ...content,

packages/core/src/session/message-updater.ts

@@ -142,6 +142,7 @@ export function update(adapter: Adapter, event: SessionEvent.Event) {
   return Effect.gen(function* () {
     yield* SessionEvent.All.match(event, {
       "session.usage.updated": () => Effect.void,
+      "session.usage.recorded": () => Effect.void,
       "session.agent.selected": (event) => {
         return adapter.appendMessage(
           SessionMessage.AgentSelected.make({

packages/core/src/session/projector.ts

@@ -609,6 +609,7 @@ const layer = Layer.effectDiscard(
         .run()
         .pipe(Effect.orDie),
     )
+    yield* events.project(SessionEvent.UsageRecorded, (event) => applyUsage(db, event.data.sessionID, event.data))
     yield* events.project(SessionEvent.Forked, (event) => projectFork(db, event))
     yield* events.project(SessionEvent.InputPromoted, (event) =>
       Effect.gen(function* () {
@@ -781,7 +782,7 @@ const layer = Layer.effectDiscard(
         yield* InstructionState.reset(db, event.data.sessionID)
       }),
     )
-    yield* events.subscribe([SessionEvent.Step.Ended, SessionEvent.Step.Failed]).pipe(
+    yield* events.subscribe([SessionEvent.Step.Ended, SessionEvent.Step.Failed, SessionEvent.UsageRecorded]).pipe(
       Stream.runForEach((event) => {
         if (
           event.type === SessionEvent.Step.Failed.type &&

packages/core/src/session/runner/llm.ts

@@ -2,11 +2,9 @@ export * as SessionRunnerLLM from "./llm"
 
 import { LLMClient, LLMError, LLMEvent, isContextOverflowFailure, type ProviderErrorEvent } from "@opencode-ai/ai"
 import { SessionError } from "@opencode-ai/schema/session-error"
-import { Money } from "@opencode-ai/schema/money"
 import { Cause, Effect, Exit, Fiber, FiberSet, Layer, Option, Semaphore, Stream } from "effect"
 import { Database } from "../../database/database"
 import { EventV2 } from "../../event"
-import { ModelV2 } from "../../model"
 import { PermissionV2 } from "../../permission"
 import { QuestionTool } from "../../tool/question"
 import { ToolOutputStore } from "../../tool-output-store"
@@ -28,30 +26,7 @@ import { llmClient } from "../../effect/app-node-platform"
 import { StepFailedError } from "../error"
 import { toSessionError } from "../to-session-error"
 import { SessionRunnerRetry } from "./retry"
-
-type StepTokens = {
-  readonly input: number
-  readonly output: number
-  readonly reasoning: number
-  readonly cache: { readonly read: number; readonly write: number }
-}
-
-// TODO(#35765): Use Copilot's reported billed amount once billing has a dedicated typed runtime contract.
-export function calculateCost(costs: ModelV2.Info["cost"], tokens: StepTokens) {
-  const context = tokens.input + tokens.cache.read + tokens.cache.write
-  const tier = costs
-    .filter((cost) => cost.tier?.type === "context" && context > cost.tier.size)
-    .toSorted((a, b) => (b.tier?.size ?? 0) - (a.tier?.size ?? 0))[0]
-  const cost = tier ?? costs.find((cost) => cost.tier === undefined)
-  if (!cost) return Money.USD.zero
-  return Money.USD.make(
-    (tokens.input * cost.input +
-      (tokens.output + tokens.reasoning) * cost.output +
-      tokens.cache.read * cost.cache.read +
-      tokens.cache.write * cost.cache.write) /
-      1_000_000,
-  )
-}
+import { SessionUsage } from "../usage"
 
 const layer = Layer.effect(
   Service,
@@ -127,7 +102,7 @@ const layer = Layer.effect(
       const agent = loaded.agent
       const resolved = loaded.model
       const model = resolved.model
-      const compactionInput = { session, messages: loaded.messages, model }
+      const compactionInput = { session, messages: loaded.messages, model, cost: resolved.cost }
       if (compaction.required(compactionInput) && !(yield* SessionPending.compaction(db, session.id))) {
         const compacted = yield* compaction.compact(compactionInput)
         if (compacted.status === "completed") return { _tag: "RestartAfterCompaction", step: currentStep } as const
@@ -216,7 +191,7 @@ const layer = Layer.effect(
       )
 
       const stepUsage = (settlement: NonNullable<ReturnType<typeof publisher.stepSettlement>>) => ({
-        cost: calculateCost(resolved.cost, settlement.tokens),
+        cost: SessionUsage.calculateCost(resolved.cost, settlement.tokens),
         tokens: settlement.tokens,
       })
 
@@ -258,7 +233,8 @@ const layer = Layer.effect(
             recoverOverflow &&
             !publisher.hasRetryEvidence() &&
             isContextOverflowFailure(overflowFailure ?? streamFailure) &&
-            (yield* restore(recoverOverflow({ session, messages: loaded.messages, model }))).status === "completed"
+            (yield* restore(recoverOverflow({ session, messages: loaded.messages, model, cost: resolved.cost })))
+              .status === "completed"
           )
             return { _tag: "RestartAfterOverflowCompaction", step: currentStep } as const
 

packages/core/src/session/runner/publish-llm-event.ts

@@ -1,4 +1,4 @@
-import { ToolOutput, type LLMEvent, type ProviderMetadata, type ToolResultValue, type Usage } from "@opencode-ai/ai"
+import { ToolOutput, type LLMEvent, type ProviderMetadata, type ToolResultValue } from "@opencode-ai/ai"
 import { Effect } from "effect"
 import { EventV2 } from "../../event"
 import { ModelV2 } from "../../model"
@@ -9,6 +9,7 @@ import { SessionError } from "@opencode-ai/schema/session-error"
 import { Money } from "@opencode-ai/schema/money"
 import { AgentV2 } from "../../agent"
 import { Snapshot } from "../../snapshot"
+import { SessionUsage } from "../usage"
 
 type Input = {
   readonly sessionID: SessionSchema.ID
@@ -19,20 +20,6 @@ type Input = {
   readonly assistantMessageID?: SessionMessage.ID
 }
 
-const safe = (value: number | undefined) => Math.max(0, Number.isFinite(value) ? (value ?? 0) : 0)
-
-const tokens = (usage: Usage | undefined) => {
-  const reasoning = safe(usage?.reasoningTokens)
-  const read = safe(usage?.cacheReadInputTokens)
-  const write = safe(usage?.cacheWriteInputTokens)
-  return {
-    input: safe(usage?.nonCachedInputTokens),
-    output: safe(usage?.visibleOutputTokens),
-    reasoning,
-    cache: { read, write },
-  }
-}
-
 const record = (value: unknown): Record<string, unknown> =>
   typeof value === "object" && value !== null && !Array.isArray(value) ? (value as Record<string, unknown>) : { value }
 
@@ -77,7 +64,7 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
   let stepSettlement:
     | {
         readonly finish: Extract<LLMEvent, { type: "step-finish" }>["reason"]
-        readonly tokens: ReturnType<typeof tokens>
+        readonly tokens: ReturnType<typeof SessionUsage.tokens>
       }
     | undefined
 
@@ -251,7 +238,7 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
 
   const publishStepFailure = Effect.fnUntraced(function* (usage?: {
     readonly cost: Money.USD
-    readonly tokens: ReturnType<typeof tokens>
+    readonly tokens: ReturnType<typeof SessionUsage.tokens>
   }) {
     if (stepFailed || stepFailure === undefined) return
     const assistantMessageID = yield* startAssistant()
@@ -429,7 +416,7 @@ export const createLLMEventPublisher = (events: Pick<EventV2.Interface, "publish
       case "step-finish":
         yield* flush()
         if (stepSettlement) return yield* Effect.die(new Error("Duplicate step finish"))
-        stepSettlement = { finish: event.reason, tokens: tokens(event.usage) }
+        stepSettlement = { finish: event.reason, tokens: SessionUsage.tokens(event.usage) }
         if (event.reason === "content-filter") {
           providerFailed = true
           yield* failAssistant({ type: "provider.content-filter", message: "Provider blocked the response" }, true)

packages/core/src/session/title.ts

@@ -1,7 +1,7 @@
 export * as SessionTitle from "./title"
 
 import { LLM, LLMClient, LLMError, LLMEvent, Message, type LLMRequest } from "@opencode-ai/ai"
-import { Context, DateTime, Effect, Layer, Stream } from "effect"
+import { Context, Effect, Layer, Stream } from "effect"
 import { AgentV2 } from "../agent"
 import { Database } from "../database/database"
 import { EventV2 } from "../event"
@@ -12,6 +12,7 @@ import { SessionHistory } from "./history"
 import { SessionModelHeaders } from "./model-headers"
 import { SessionRunnerModel } from "./runner/model"
 import { SessionSchema } from "./schema"
+import { SessionUsage } from "./usage"
 
 const MAX_LENGTH = 100
 
@@ -51,6 +52,16 @@ const make = (dependencies: Dependencies) => {
     if (!resolved) return
     const chunks: string[] = []
     let failed = false
+    let usage: SessionUsage.Recorded | undefined
+    const recordUsage = Effect.suspend(() =>
+      usage
+        ? dependencies.events.publish(SessionEvent.UsageRecorded, {
+            sessionID: session.id,
+            source: "title",
+            ...usage,
+          })
+        : Effect.void,
+    )
     const streamed = yield* dependencies.llm
       .stream(
         LLM.request({
@@ -65,11 +76,17 @@ const make = (dependencies: Dependencies) => {
         Stream.runForEach((event) => {
           if (LLMEvent.is.providerError(event)) failed = true
           if (LLMEvent.is.textDelta(event)) chunks.push(event.text)
+          if (LLMEvent.is.stepFinish(event)) {
+            const step = SessionUsage.record(event.usage, resolved.cost)
+            usage = usage ? SessionUsage.add(usage, step) : step
+          }
           return Effect.void
         }),
         Effect.as(true),
         Effect.catchTag("LLM.Error", () => Effect.succeed(false)),
+        Effect.onInterrupt(() => recordUsage.pipe(Effect.asVoid)),
       )
+    yield* recordUsage
     if (!streamed || failed) return
     const title = chunks
       .join("")

packages/core/src/session/usage.ts

@@ -0,0 +1,55 @@
+export * as SessionUsage from "./usage"
+
+import type { Usage } from "@opencode-ai/ai"
+import { Money } from "@opencode-ai/schema/money"
+import type { TokenUsage } from "@opencode-ai/schema/token-usage"
+import type { ModelV2 } from "../model"
+
+const safe = (value: number | undefined) => Math.max(0, Number.isFinite(value) ? (value ?? 0) : 0)
+
+export const tokens = (usage: Usage | undefined): TokenUsage.Info => ({
+  input: safe(usage?.nonCachedInputTokens),
+  output: safe(usage?.visibleOutputTokens),
+  reasoning: safe(usage?.reasoningTokens),
+  cache: {
+    read: safe(usage?.cacheReadInputTokens),
+    write: safe(usage?.cacheWriteInputTokens),
+  },
+})
+
+// TODO(#35765): Use Copilot's reported billed amount once billing has a dedicated typed runtime contract.
+export function calculateCost(costs: ModelV2.Info["cost"], usage: TokenUsage.Info) {
+  const context = usage.input + usage.cache.read + usage.cache.write
+  const tier = costs
+    .filter((cost) => cost.tier?.type === "context" && context > cost.tier.size)
+    .toSorted((a, b) => (b.tier?.size ?? 0) - (a.tier?.size ?? 0))[0]
+  const cost = tier ?? costs.find((cost) => cost.tier === undefined)
+  if (!cost) return Money.USD.zero
+  return Money.USD.make(
+    (usage.input * cost.input +
+      (usage.output + usage.reasoning) * cost.output +
+      usage.cache.read * cost.cache.read +
+      usage.cache.write * cost.cache.write) /
+      1_000_000,
+  )
+}
+
+export type Recorded = { readonly tokens: TokenUsage.Info; readonly cost: Money.USD }
+
+export const record = (usage: Usage | undefined, costs: ModelV2.Info["cost"]): Recorded => {
+  const normalized = tokens(usage)
+  return { tokens: normalized, cost: calculateCost(costs, normalized) }
+}
+
+export const add = (a: Recorded, b: Recorded): Recorded => ({
+  cost: Money.USD.make(a.cost + b.cost),
+  tokens: {
+    input: a.tokens.input + b.tokens.input,
+    output: a.tokens.output + b.tokens.output,
+    reasoning: a.tokens.reasoning + b.tokens.reasoning,
+    cache: {
+      read: a.tokens.cache.read + b.tokens.cache.read,
+      write: a.tokens.cache.write + b.tokens.cache.write,
+    },
+  },
+})

packages/core/test/session-compaction.test.ts

@@ -21,6 +21,7 @@ import { ProjectTable } from "@opencode-ai/core/project/sql"
 import { Flag } from "@opencode-ai/core/flag/flag"
 import { InstallationVersion } from "@opencode-ai/core/installation/version"
 import { AbsolutePath } from "@opencode-ai/core/schema"
+import { Money } from "@opencode-ai/schema/money"
 import { DateTime, Effect, Fiber, Layer, Stream } from "effect"
 import { asc, eq } from "drizzle-orm"
 import { testEffect } from "./lib/effect"
@@ -31,17 +32,44 @@ const model = Model.make({
   provider: "test",
   route: OpenAIChat.route.with({ limits: { context: 10_000, output: 1_000 } }),
 })
+const cost = [
+  {
+    input: Money.USDPerMillionTokens.make(1),
+    output: Money.USDPerMillionTokens.make(2),
+    cache: {
+      read: Money.USDPerMillionTokens.make(0.1),
+      write: Money.USDPerMillionTokens.make(0.5),
+    },
+  },
+]
 const client = Layer.mock(LLMClient.Service)({
   prepare: () => Effect.die("unused"),
   stream: (request: LLMRequest) => {
     requests.push(request)
-    return Stream.make(LLMEvent.textDelta({ id: "summary", text: "manual summary" }))
+    return Stream.make(
+      LLMEvent.textDelta({ id: "summary", text: "manual summary" }),
+      LLMEvent.stepFinish({
+        index: 0,
+        reason: "stop",
+        usage: {
+          inputTokens: 15,
+          outputTokens: 6,
+          nonCachedInputTokens: 10,
+          cacheReadInputTokens: 3,
+          cacheWriteInputTokens: 2,
+          reasoningTokens: 2,
+        },
+      }),
+      LLMEvent.finish({
+        reason: "stop",
+      }),
+    )
   },
   generate: () => Effect.die("unused"),
 })
 const config = Layer.mock(Config.Service)({ entries: () => Effect.succeed([]) })
 const models = Layer.mock(SessionRunnerModel.Service)({
-  resolve: () => Effect.succeed(SessionRunnerModel.resolved(model)),
+  resolve: () => Effect.succeed(SessionRunnerModel.resolved(model, undefined, cost)),
 })
 const it = testEffect(
   AppNodeBuilder.build(
@@ -169,6 +197,10 @@ it.effect("manual compaction summarizes short context instead of no-op", () =>
     expect(yield* store.context(sessionID)).toMatchObject([
       { type: "compaction", reason: "manual", summary: "manual summary", recent: "" },
     ])
+    expect(yield* store.get(sessionID)).toMatchObject({
+      cost: 0.0000233,
+      tokens: { input: 10, output: 4, reasoning: 2, cache: { read: 3, write: 2 } },
+    })
     expect(
       yield* db
         .select({ type: EventTable.type })
@@ -179,6 +211,7 @@ it.effect("manual compaction summarizes short context instead of no-op", () =>
         .pipe(Effect.orDie),
     ).toEqual([
       { type: EventV2.versionedType(SessionEvent.Compaction.Started.type, 1) },
+      { type: EventV2.versionedType(SessionEvent.UsageRecorded.type, 1) },
       { type: EventV2.versionedType(SessionEvent.Compaction.Ended.type, 1) },
     ])
   }),

packages/core/test/session-runner.test.ts

@@ -42,6 +42,7 @@ import { SessionRunCoordinator } from "@opencode-ai/core/session/run-coordinator
 import { SessionRunner } from "@opencode-ai/core/session/runner"
 import * as SessionRunnerLLM from "@opencode-ai/core/session/runner/llm"
 import { SessionRunnerModel } from "@opencode-ai/core/session/runner/model"
+import { SessionUsage } from "@opencode-ai/core/session/usage"
 import { ToolRegistry } from "@opencode-ai/core/tool/registry"
 import { PluginSupervisor } from "@opencode-ai/core/plugin/supervisor"
 import { PluginHooks } from "@opencode-ai/core/plugin/hooks"
@@ -165,7 +166,7 @@ const recoveryModel = Model.make({
 
 test("calculates step cost using the matching context tier", () => {
   expect(
-    SessionRunnerLLM.calculateCost(
+    SessionUsage.calculateCost(
       [
         {
           input: Money.USDPerMillionTokens.make(1),
@@ -192,7 +193,7 @@ test("calculates step cost using the matching context tier", () => {
 
 test("does not apply an ineligible tier without base pricing", () => {
   expect(
-    SessionRunnerLLM.calculateCost(
+    SessionUsage.calculateCost(
       [
         {
           tier: { type: "context", size: 100 },

packages/core/test/session-title.test.ts

@@ -20,7 +20,8 @@ import { ProjectTable } from "@opencode-ai/core/project/sql"
 import { Flag } from "@opencode-ai/core/flag/flag"
 import { InstallationVersion } from "@opencode-ai/core/installation/version"
 import { AbsolutePath } from "@opencode-ai/core/schema"
-import { DateTime, Effect, Layer, Stream } from "effect"
+import { Money } from "@opencode-ai/schema/money"
+import { Effect, Layer, Stream } from "effect"
 import { testEffect } from "./lib/effect"
 
 let requests: LLMRequest[] = []
@@ -29,16 +30,43 @@ const model = Model.make({
   provider: "test",
   route: OpenAIChat.route.with({ limits: { context: 10_000, output: 1_000 } }),
 })
+const cost = [
+  {
+    input: Money.USDPerMillionTokens.make(1),
+    output: Money.USDPerMillionTokens.make(2),
+    cache: {
+      read: Money.USDPerMillionTokens.make(0.1),
+      write: Money.USDPerMillionTokens.make(0.5),
+    },
+  },
+]
 const client = Layer.mock(LLMClient.Service)({
   prepare: () => Effect.die("unused"),
   stream: (request: LLMRequest) => {
     requests.push(request)
-    return Stream.make(LLMEvent.textDelta({ id: "title", text: "Generated Title\n" }))
+    return Stream.make(
+      LLMEvent.textDelta({ id: "title", text: "Generated Title\n" }),
+      LLMEvent.stepFinish({
+        index: 0,
+        reason: "stop",
+        usage: {
+          inputTokens: 15,
+          outputTokens: 6,
+          nonCachedInputTokens: 10,
+          cacheReadInputTokens: 3,
+          cacheWriteInputTokens: 2,
+          reasoningTokens: 2,
+        },
+      }),
+      LLMEvent.finish({
+        reason: "stop",
+      }),
+    )
   },
   generate: () => Effect.die("unused"),
 })
 const models = Layer.mock(SessionRunnerModel.Service)({
-  resolve: () => Effect.succeed(SessionRunnerModel.resolved(model)),
+  resolve: () => Effect.succeed(SessionRunnerModel.resolved(model, undefined, cost)),
 })
 const it = testEffect(
   AppNodeBuilder.build(
@@ -130,6 +158,8 @@ it.effect("generates a title from the sole user message and renames the session"
     expect(JSON.stringify(requests[0]?.messages)).toContain("Help me debug the failing build")
     const renamed = yield* store.get(sessionID)
     expect(renamed?.title).toBe("Generated Title")
+    expect(renamed?.tokens).toEqual({ input: 10, output: 4, reasoning: 2, cache: { read: 3, write: 2 } })
+    expect(renamed?.cost).toBeCloseTo(0.0000233)
   }),
 )
 

packages/schema/src/session-event.ts

@@ -86,6 +86,18 @@ export const Renamed = Event.durable({
 })
 export type Renamed = typeof Renamed.Type
 
+export const UsageRecorded = Event.durable({
+  type: "session.usage.recorded",
+  ...options,
+  schema: {
+    ...Base,
+    source: Schema.Literals(["title", "compaction"]),
+    cost: Money.USD,
+    tokens: TokenUsage.Info,
+  },
+})
+export type UsageRecorded = typeof UsageRecorded.Type
+
 export const UsageUpdated = Event.ephemeral({
   type: "session.usage.updated",
   schema: {
@@ -569,8 +581,10 @@ export const Definitions = Event.inventory(
   RevertEvent.Committed,
 )
 
+// UsageRecorded is durable but internal: excluded from Definitions so it never reaches the public manifest.
 export const DurableDefinitions = Event.inventory(
   ...Definitions.filter((definition) => definition.durability === "durable"),
+  UsageRecorded,
 )
 
 export const Durable = Schema.Union(DurableDefinitions, { mode: "oneOf" })
@@ -578,6 +592,8 @@ export const Durable = Schema.Union(DurableDefinitions, { mode: "oneOf" })
   .annotate({ identifier: "Session.Event.Durable" })
 export type DurableEvent = typeof Durable.Type
 
-export const All = Schema.Union(Definitions, { mode: "oneOf" }).pipe(Schema.toTaggedUnion("type"))
+export const All = Schema.Union(Event.inventory(...Definitions, UsageRecorded), { mode: "oneOf" }).pipe(
+  Schema.toTaggedUnion("type"),
+)
 export type Event = typeof All.Type
 export type Type = Event["type"]

packages/schema/test/event-manifest.test.ts

@@ -104,6 +104,7 @@ describe("public event manifest", () => {
         "session.model.selected.1",
         "session.moved.1",
         "session.renamed.1",
+        "session.usage.recorded.1",
         "session.forked.2",
         "session.input.promoted.1",
         "session.input.admitted.1",
@@ -139,9 +140,16 @@ describe("public event manifest", () => {
         "session.revert.committed.1",
       ].toSorted(),
     )
-    expect(SessionEvent.DurableDefinitions).toEqual(
-      SessionEvent.Definitions.filter((definition) => definition.durability === "durable"),
-    )
+    expect(SessionEvent.DurableDefinitions).toEqual([
+      ...SessionEvent.Definitions.filter((definition) => definition.durability === "durable"),
+      SessionEvent.UsageRecorded,
+    ])
+    expect(SessionEvent.UsageRecorded.durability).toBe("durable")
+    expect(EventManifest.Durable.get("session.usage.recorded.1")).toBe(SessionEvent.UsageRecorded)
+    expect(SessionEvent.Definitions).not.toContain(SessionEvent.UsageRecorded)
+    expect(EventManifest.Definitions).not.toContain(SessionEvent.UsageRecorded)
+    expect(EventManifest.ServerDefinitions).not.toContain(SessionEvent.UsageRecorded)
+    expect(EventManifest.Latest.has("session.usage.recorded")).toBe(false)
     expect(SessionEvent.UsageUpdated.durability).toBe("ephemeral")
     expect(SessionEvent.Compaction.Delta.durability).toBe("ephemeral")
     expect(EventManifest.Durable.has("session.compaction.delta.1")).toBe(false)