diff --git a/packages/app/src/components/session-context-usage.tsx b/packages/app/src/components/session-context-usage.tsx
index c6e60d3edebd..7d84d9798f2b 100644
--- a/packages/app/src/components/session-context-usage.tsx
+++ b/packages/app/src/components/session-context-usage.tsx
@@ -1,4 +1,4 @@
-import { Match, Show, Switch, createMemo } from "solid-js"
+import { Match, Show, Switch, createMemo, createEffect } from "solid-js"
 import { Tooltip } from "@opencode-ai/ui/tooltip"
 import { ProgressCircle } from "@opencode-ai/ui/progress-circle"
 import { Button } from "@opencode-ai/ui/button"
@@ -44,7 +44,15 @@ export function SessionContextUsage(props: SessionContextUsageProps) {
       }),
   )
 
-  const metrics = createMemo(() => getSessionContextMetrics(messages(), sync.data.provider.all))
+  const metrics = createMemo(() => getSessionContextMetrics(messages(), sync.data.provider.all, sync.data))
+  createEffect(() => {
+    const missing = metrics().missing
+    if (missing.length > 0) {
+      for (const id of missing) {
+        sync.session.sync(id)
+      }
+    }
+  })
   const context = createMemo(() => metrics().context)
   const cost = createMemo(() => {
     return usd().format(metrics().totalCost)
@@ -92,16 +100,22 @@ export function SessionContextUsage(props: SessionContextUsageProps) {
     <Show when={params.id}>
       <Tooltip value={tooltipValue()} placement="top">
         <Switch>
-          <Match when={variant() === "indicator"}>{circle()}</Match>
+          <Match when={variant() === "indicator"}>
+            <div class="flex items-center gap-1.5">
+              {circle()}
+              <span class="text-12-regular text-text-weak">{cost()}</span>
+            </div>
+          </Match>
           <Match when={true}>
             <Button
               type="button"
               variant="ghost"
-              class="size-6"
+              class="h-6 px-1 flex items-center gap-1.5"
               onClick={openContext}
               aria-label={language.t("context.usage.view")}
             >
               {circle()}
+              <span class="text-12-regular text-text-weak">{cost()}</span>
             </Button>
           </Match>
         </Switch>
diff --git a/packages/app/src/components/session/session-context-metrics.test.ts b/packages/app/src/components/session/session-context-metrics.test.ts
index 0e109a71bdac..b980700795dc 100644
--- a/packages/app/src/components/session/session-context-metrics.test.ts
+++ b/packages/app/src/components/session/session-context-metrics.test.ts
@@ -8,9 +8,11 @@ const assistant = (
   cost: number,
   providerID = "openai",
   modelID = "gpt-4.1",
+  sessionID = "s1",
 ) => {
   return {
     id,
+    sessionID,
     role: "assistant",
     providerID,
     modelID,
@@ -28,9 +30,10 @@ const assistant = (
   } as unknown as Message
 }
 
-const user = (id: string) => {
+const user = (id: string, sessionID = "s1") => {
   return {
     id,
+    sessionID,
     role: "user",
     cost: 0,
     time: { created: 1 },
@@ -98,4 +101,44 @@ describe("getSessionContextMetrics", () => {
     expect(metrics.totalCost).toBe(0)
     expect(metrics.context).toBeUndefined()
   })
+
+  test("computes costs with store including sub-agents", () => {
+    const messages = [
+      assistant("a1", { input: 10, output: 10, reasoning: 0, read: 0, write: 0 }, 0.5, "openai", "gpt-4.1", "s1"),
+    ]
+    const store = {
+      message: {
+        s1: [{ id: "a1", role: "assistant", cost: 0.5 }],
+        s2: [{ id: "a2", role: "assistant", cost: 1.0 }],
+      },
+      part: {
+        a1: [{ type: "tool", tool: "task", state: { metadata: { sessionId: "s2" } } }],
+      },
+    }
+
+    const metrics = getSessionContextMetrics(messages, [], store)
+
+    expect(metrics.totalCost).toBe(1.5)
+    expect(metrics.ownCost).toBe(0.5)
+    expect(metrics.missing).toEqual([])
+  })
+
+  test("identifies missing child sessions in store", () => {
+    const messages = [
+      assistant("a1", { input: 10, output: 10, reasoning: 0, read: 0, write: 0 }, 0.5, "openai", "gpt-4.1", "s1"),
+    ]
+    const store = {
+      message: {
+        s1: [{ id: "a1", role: "assistant", cost: 0.5 }],
+      },
+      part: {
+        a1: [{ type: "tool", tool: "task", state: { metadata: { sessionId: "s2" } } }],
+      },
+    }
+
+    const metrics = getSessionContextMetrics(messages, [], store)
+
+    expect(metrics.totalCost).toBe(0.5)
+    expect(metrics.missing).toEqual(["s2"])
+  })
 })
diff --git a/packages/app/src/components/session/session-context-metrics.ts b/packages/app/src/components/session/session-context-metrics.ts
index 0789b05f1730..2846e5db6040 100644
--- a/packages/app/src/components/session/session-context-metrics.ts
+++ b/packages/app/src/components/session/session-context-metrics.ts
@@ -1,3 +1,4 @@
+import { costs, type CostStore } from "@opencode-ai/util/cost"
 import type { AssistantMessage, Message } from "@opencode-ai/sdk/v2/client"
 
 type Provider = {
@@ -31,6 +32,8 @@ type Context = {
 
 type Metrics = {
   totalCost: number
+  ownCost: number
+  missing: string[]
   context: Context | undefined
 }
 
@@ -42,15 +45,25 @@ const lastAssistantWithTokens = (messages: Message[]) => {
   for (let i = messages.length - 1; i >= 0; i--) {
     const msg = messages[i]
     if (msg.role !== "assistant") continue
-    if (tokenTotal(msg) <= 0) continue
-    return msg
+    if (tokenTotal(msg as AssistantMessage) <= 0) continue
+    return msg as AssistantMessage
   }
 }
 
-const build = (messages: Message[] = [], providers: Provider[] = []): Metrics => {
-  const totalCost = messages.reduce((sum, msg) => sum + (msg.role === "assistant" ? msg.cost : 0), 0)
+const build = (messages: Message[] = [], providers: Provider[] = [], store?: CostStore): Metrics => {
+  const id = messages[0]?.sessionID
+  const result = store && id ? costs(id, store) : undefined
+
   const message = lastAssistantWithTokens(messages)
-  if (!message) return { totalCost, context: undefined }
+  if (!message)
+    return {
+      totalCost: result
+        ? result.total
+        : messages.reduce((sum, msg) => sum + (msg.role === "assistant" ? msg.cost : 0), 0),
+      ownCost: result ? result.own : 0,
+      missing: result ? result.missing : [],
+      context: undefined,
+    }
 
   const provider = providers.find((item) => item.id === message.providerID)
   const model = provider?.models[message.modelID]
@@ -58,7 +71,11 @@ const build = (messages: Message[] = [], providers: Provider[] = []): Metrics =>
   const total = tokenTotal(message)
 
   return {
-    totalCost,
+    totalCost: result
+      ? result.total
+      : messages.reduce((sum, msg) => sum + (msg.role === "assistant" ? msg.cost : 0), 0),
+    ownCost: result ? result.own : 0,
+    missing: result ? result.missing : [],
     context: {
       message,
       provider,
@@ -77,6 +94,6 @@ const build = (messages: Message[] = [], providers: Provider[] = []): Metrics =>
   }
 }
 
-export function getSessionContextMetrics(messages: Message[] = [], providers: Provider[] = []) {
-  return build(messages, providers)
+export function getSessionContextMetrics(messages: Message[] = [], providers: Provider[] = [], store?: CostStore) {
+  return build(messages, providers, store)
 }
diff --git a/packages/app/src/components/session/session-context-tab.tsx b/packages/app/src/components/session/session-context-tab.tsx
index 81220b3adb2f..99e77415368b 100644
--- a/packages/app/src/components/session/session-context-tab.tsx
+++ b/packages/app/src/components/session/session-context-tab.tsx
@@ -104,7 +104,15 @@ export function SessionContextTab(props: SessionContextTabProps) {
       }),
   )
 
-  const metrics = createMemo(() => getSessionContextMetrics(props.messages(), sync.data.provider.all))
+  const metrics = createMemo(() => getSessionContextMetrics(props.messages(), sync.data.provider.all, sync.data))
+  createEffect(() => {
+    const missing = metrics().missing
+    if (missing.length > 0) {
+      for (const id of missing) {
+        sync.session.sync(id)
+      }
+    }
+  })
   const ctx = createMemo(() => metrics().context)
   const formatter = createMemo(() => createSessionContextFormatter(language.locale()))
 
diff --git a/packages/app/src/custom-elements.d.ts b/packages/app/src/custom-elements.d.ts
index e4ea0d6cebda..86cb284693e6 120000
--- a/packages/app/src/custom-elements.d.ts
+++ b/packages/app/src/custom-elements.d.ts
@@ -1 +1 @@
-../../ui/src/custom-elements.d.ts
\ No newline at end of file
+/// <reference path="../../ui/src/custom-elements.d.ts" />
diff --git a/packages/enterprise/src/custom-elements.d.ts b/packages/enterprise/src/custom-elements.d.ts
index e4ea0d6cebda..86cb284693e6 120000
--- a/packages/enterprise/src/custom-elements.d.ts
+++ b/packages/enterprise/src/custom-elements.d.ts
@@ -1 +1 @@
-../../ui/src/custom-elements.d.ts
\ No newline at end of file
+/// <reference path="../../ui/src/custom-elements.d.ts" />
diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/header.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/header.tsx
index 0c5ea9a85723..e605c5b98673 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/header.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/header.tsx
@@ -1,6 +1,7 @@
 import { type Accessor, createMemo, createSignal, Match, Show, Switch } from "solid-js"
 import { useRouteData } from "@tui/context/route"
 import { useSync } from "@tui/context/sync"
+import { costs } from "@opencode-ai/util/cost"
 import { pipe, sumBy } from "remeda"
 import { useTheme } from "@tui/context/theme"
 import { SplitBorder } from "@tui/component/border"
@@ -36,14 +37,11 @@ export function Header() {
   const messages = createMemo(() => sync.data.message[route.sessionID] ?? [])
 
   const cost = createMemo(() => {
-    const total = pipe(
-      messages(),
-      sumBy((x) => (x.role === "assistant" ? x.cost : 0)),
-    )
+    const result = costs(route.sessionID, sync.data)
     return new Intl.NumberFormat("en-US", {
       style: "currency",
       currency: "USD",
-    }).format(total)
+    }).format(result.total)
   })
 
   const context = createMemo(() => {
diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
index e83b9abe98ae..06b9d40d4151 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
@@ -15,6 +15,7 @@ import { Dynamic } from "solid-js/web"
 import path from "path"
 import { useRoute, useRouteData } from "@tui/context/route"
 import { useSync } from "@tui/context/sync"
+import { costs } from "@opencode-ai/util/cost"
 import { SplitBorder } from "@tui/component/border"
 import { Spinner } from "@tui/component/spinner"
 import { selectedForeground, useTheme } from "@tui/context/theme"
@@ -191,6 +192,15 @@ export function Session() {
       })
   })
 
+  createEffect(() => {
+    const result = costs(route.sessionID, sync.data)
+    if (result.missing.length > 0) {
+      for (const id of result.missing) {
+        sync.session.sync(id)
+      }
+    }
+  })
+
   const toast = useToast()
   const sdk = useSDK()
 
@@ -1879,6 +1889,18 @@ function Task(props: ToolProps<typeof TaskTool>) {
             <text style={{ fg: theme.textMuted }}>
               {props.input.description} ({tools().length} toolcalls)
             </text>
+            <Show when={props.metadata.sessionId}>
+              {(sessionId) => {
+                const result = createMemo(() => costs(sessionId(), sync.data))
+                const total = createMemo(() =>
+                  new Intl.NumberFormat("en-US", {
+                    style: "currency",
+                    currency: "USD",
+                  }).format(result().total),
+                )
+                return <text style={{ fg: theme.textMuted }}>({total})</text>
+              }}
+            </Show>
             <Show when={current()}>
               {(item) => {
                 const title = item().state.status === "completed" ? (item().state as any).title : ""
diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/sidebar.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/sidebar.tsx
index 4ffe91558ed7..c005bfcf310c 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/sidebar.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/sidebar.tsx
@@ -1,4 +1,5 @@
 import { useSync } from "@tui/context/sync"
+import { costs } from "@opencode-ai/util/cost"
 import { createMemo, For, Show, Switch, Match } from "solid-js"
 import { createStore } from "solid-js/store"
 import { useTheme } from "../../context/theme"
@@ -41,11 +42,11 @@ export function Sidebar(props: { sessionID: string; overlay?: boolean }) {
   )
 
   const cost = createMemo(() => {
-    const total = messages().reduce((sum, x) => sum + (x.role === "assistant" ? x.cost : 0), 0)
+    const result = costs(props.sessionID, sync.data)
     return new Intl.NumberFormat("en-US", {
       style: "currency",
       currency: "USD",
-    }).format(total)
+    }).format(result.total)
   })
 
   const context = createMemo(() => {
diff --git a/packages/opencode/src/session/index.ts b/packages/opencode/src/session/index.ts
index 255f4dd46010..446408d11418 100644
--- a/packages/opencode/src/session/index.ts
+++ b/packages/opencode/src/session/index.ts
@@ -581,22 +581,30 @@ export namespace Session {
   export const updateMessage = fn(MessageV2.Info, async (msg) => {
     const time_created = msg.role === "user" ? msg.time.created : msg.time.created
     const { id, sessionID, ...data } = msg
-    Database.use((db) => {
-      db.insert(MessageTable)
-        .values({
-          id,
-          session_id: sessionID,
-          time_created,
-          data,
-        })
-        .onConflictDoUpdate({ target: MessageTable.id, set: { data } })
-        .run()
-      Database.effect(() =>
-        Bus.publish(MessageV2.Event.Updated, {
-          info: msg,
-        }),
-      )
-    })
+    try {
+      Database.use((db) => {
+        db.insert(MessageTable)
+          .values({
+            id,
+            session_id: sessionID,
+            time_created,
+            data,
+          })
+          .onConflictDoUpdate({ target: MessageTable.id, set: { data } })
+          .run()
+        Database.effect(() =>
+          Bus.publish(MessageV2.Event.Updated, {
+            info: msg,
+          }),
+        )
+      })
+    } catch (e) {
+      if (e instanceof Error && e.message.includes("FOREIGN KEY constraint failed")) {
+        log.warn("ignoring message update for missing session", { sessionID, messageID: id })
+        return msg
+      }
+      throw e
+    }
     return msg
   })
 
@@ -646,23 +654,31 @@ export namespace Session {
   export const updatePart = fn(UpdatePartInput, async (part) => {
     const { id, messageID, sessionID, ...data } = part
     const time = Date.now()
-    Database.use((db) => {
-      db.insert(PartTable)
-        .values({
-          id,
-          message_id: messageID,
-          session_id: sessionID,
-          time_created: time,
-          data,
-        })
-        .onConflictDoUpdate({ target: PartTable.id, set: { data } })
-        .run()
-      Database.effect(() =>
-        Bus.publish(MessageV2.Event.PartUpdated, {
-          part,
-        }),
-      )
-    })
+    try {
+      Database.use((db) => {
+        db.insert(PartTable)
+          .values({
+            id,
+            message_id: messageID,
+            session_id: sessionID,
+            time_created: time,
+            data,
+          })
+          .onConflictDoUpdate({ target: PartTable.id, set: { data } })
+          .run()
+        Database.effect(() =>
+          Bus.publish(MessageV2.Event.PartUpdated, {
+            part,
+          }),
+        )
+      })
+    } catch (e) {
+      if (e instanceof Error && e.message.includes("FOREIGN KEY constraint failed")) {
+        log.warn("ignoring part update for missing message/session", { sessionID, messageID, partID: id })
+        return part
+      }
+      throw e
+    }
     return part
   })
 
diff --git a/packages/ui/src/components/message-part.tsx b/packages/ui/src/components/message-part.tsx
index 3f61b3186d30..f4862b48accb 100644
--- a/packages/ui/src/components/message-part.tsx
+++ b/packages/ui/src/components/message-part.tsx
@@ -45,6 +45,7 @@ import { ImagePreview } from "./image-preview"
 import { findLast } from "@opencode-ai/util/array"
 import { getDirectory as _getDirectory, getFilename } from "@opencode-ai/util/path"
 import { checksum } from "@opencode-ai/util/encode"
+import { costs } from "@opencode-ai/util/cost"
 import { Tooltip } from "./tooltip"
 import { IconButton } from "./icon-button"
 import { createAutoScroll } from "../hooks"
@@ -921,6 +922,52 @@ ToolRegistry.register({
       }, 50)
     }
 
+    const stats = createMemo(() => {
+      const sid = childSessionId()
+      if (!sid) return undefined
+      const messages = data.store.message[sid]
+      if (!messages || messages.length === 0) return undefined
+
+      const last = findLast(
+        messages,
+        (m) =>
+          m.role === "assistant" &&
+          (m as AssistantMessage).tokens.input +
+            (m as AssistantMessage).tokens.output +
+            (m as AssistantMessage).tokens.reasoning >
+            0,
+      ) as AssistantMessage | undefined
+      if (!last) return undefined
+
+      const tokens =
+        last.tokens.input +
+        last.tokens.output +
+        last.tokens.reasoning +
+        last.tokens.cache.read +
+        last.tokens.cache.write
+      const limit = (data.store as any).provider?.all
+        ? (() => {
+            const providers = (data.store as any).provider.all as {
+              id: string
+              models: Record<string, { limit: { context: number } } | undefined>
+            }[]
+            const p = providers.find((item) => item.id === last.providerID)
+            return p?.models[last.modelID]?.limit.context
+          })()
+        : undefined
+      const usage = limit ? Math.round((tokens / limit) * 100) : undefined
+      const result = costs(sid, data.store)
+      return { tokens, usage, total: result.total, missing: result.missing }
+    })
+    createEffect(() => {
+      const missing = stats()?.missing
+      if (missing && missing.length > 0) {
+        for (const id of missing) {
+          data.syncSession?.(id)
+        }
+      }
+    })
+
     const trigger = () => (
       <div data-slot="basic-tool-tool-info-structured">
         <div data-slot="basic-tool-tool-info-main">
@@ -941,6 +988,15 @@ ToolRegistry.register({
               </Match>
             </Switch>
           </Show>
+          <Show when={stats()}>
+            {(s) => (
+              <span data-slot="basic-tool-tool-subtitle">
+                {s().tokens.toLocaleString() + " tokens"}
+                {s().usage !== undefined ? ` (${s().usage}%)` : ""}
+                {` ($${s().total.toFixed(2)})`}
+              </span>
+            )}
+          </Show>
         </div>
       </div>
     )
diff --git a/packages/util/src/cost.test.ts b/packages/util/src/cost.test.ts
new file mode 100644
index 000000000000..79b426864512
--- /dev/null
+++ b/packages/util/src/cost.test.ts
@@ -0,0 +1,111 @@
+import { expect, test } from "bun:test"
+import { costs } from "./cost"
+
+test("no sub-agents", () => {
+  const store = {
+    message: {
+      s1: [
+        { id: "m1", role: "user", cost: 0 },
+        { id: "m2", role: "assistant", cost: 0.5 },
+      ],
+    },
+    part: {},
+  }
+  const result = costs("s1", store as any)
+  expect(result.own).toBe(0.5)
+  expect(result.total).toBe(0.5)
+  expect(result.missing).toEqual([])
+})
+
+test("one loaded sub-agent", () => {
+  const store = {
+    message: {
+      s1: [{ id: "m1", role: "assistant", cost: 0.5 }],
+      s2: [{ id: "m2", role: "assistant", cost: 1.0 }],
+    },
+    part: {
+      m1: [{ type: "tool", tool: "task", state: { metadata: { sessionId: "s2" } } }],
+    },
+  }
+  const result = costs("s1", store as any)
+  expect(result.own).toBe(0.5)
+  expect(result.total).toBe(1.5)
+  expect(result.missing).toEqual([])
+})
+
+test("nested sub-agents", () => {
+  const store = {
+    message: {
+      s1: [{ id: "m1", role: "assistant", cost: 0.5 }],
+      s2: [{ id: "m2", role: "assistant", cost: 1.0 }],
+      s3: [{ id: "m3", role: "assistant", cost: 2.0 }],
+    },
+    part: {
+      m1: [{ type: "tool", tool: "task", state: { metadata: { sessionId: "s2" } } }],
+      m2: [{ type: "tool", tool: "task", state: { metadata: { sessionId: "s3" } } }],
+    },
+  }
+  const result = costs("s1", store as any)
+  expect(result.own).toBe(0.5)
+  expect(result.total).toBe(3.5)
+  expect(result.missing).toEqual([])
+})
+
+test("cycle detection", () => {
+  const store = {
+    message: {
+      s1: [{ id: "m1", role: "assistant", cost: 0.5 }],
+      s2: [{ id: "m2", role: "assistant", cost: 1.0 }],
+    },
+    part: {
+      m1: [{ type: "tool", tool: "task", state: { metadata: { sessionId: "s2" } } }],
+      m2: [{ type: "tool", tool: "task", state: { metadata: { sessionId: "s1" } } }],
+    },
+  }
+  const result = costs("s1", store as any)
+  expect(result.own).toBe(0.5)
+  expect(result.total).toBe(1.5)
+  expect(result.missing).toEqual([])
+})
+
+test("missing child session", () => {
+  const store = {
+    message: {
+      s1: [{ id: "m1", role: "assistant", cost: 0.5 }],
+    },
+    part: {
+      m1: [{ type: "tool", tool: "task", state: { metadata: { sessionId: "s2" } } }],
+    },
+  }
+  const result = costs("s1", store as any)
+  expect(result.own).toBe(0.5)
+  expect(result.total).toBe(0.5)
+  expect(result.missing).toEqual(["s2"])
+})
+
+test("empty or undefined messages", () => {
+  const store = {
+    message: {},
+    part: {},
+  }
+  const result = costs("s1", store as any)
+  expect(result.own).toBe(0)
+  expect(result.total).toBe(0)
+  expect(result.missing).toEqual(["s1"])
+})
+
+test("only assistant messages counted", () => {
+  const store = {
+    message: {
+      s1: [
+        { id: "m1", role: "user", cost: 100 },
+        { id: "m2", role: "assistant", cost: 0.5 },
+        { id: "m3", role: "system", cost: 100 },
+      ],
+    },
+    part: {},
+  }
+  const result = costs("s1", store as any)
+  expect(result.own).toBe(0.5)
+  expect(result.total).toBe(0.5)
+})
diff --git a/packages/util/src/cost.ts b/packages/util/src/cost.ts
new file mode 100644
index 000000000000..dfb40de6dc72
--- /dev/null
+++ b/packages/util/src/cost.ts
@@ -0,0 +1,52 @@
+export interface CostMessage {
+  id: string
+  role: string
+  cost?: number
+}
+
+export interface CostPart {
+  type: string
+  tool?: string
+  state?: Record<string, unknown>
+}
+
+export interface CostStore {
+  message: Record<string, CostMessage[] | undefined>
+  part: Record<string, CostPart[] | undefined>
+}
+
+export function costs(id: string, store: CostStore) {
+  const missing: string[] = []
+  const visited = new Set<string>()
+
+  const walk = (sid: string): number => {
+    if (visited.has(sid)) return 0
+    visited.add(sid)
+
+    const messages = store.message[sid]
+    if (!messages) {
+      missing.push(sid)
+      return 0
+    }
+
+    return messages
+      .filter((msg) => msg.role === "assistant")
+      .reduce((sum, msg) => {
+        const parts = store.part[msg.id] ?? []
+        const subCosts = parts
+          .filter((part) => part.type === "tool" && part.tool === "task")
+          .map((part) => (part.state?.metadata as Record<string, unknown> | undefined)?.sessionId)
+          .filter((child): child is string => typeof child === "string")
+          .reduce((acc, child) => acc + walk(child), 0)
+        return sum + (msg.cost ?? 0) + subCosts
+      }, 0)
+  }
+
+  const own = (store.message[id] ?? [])
+    .filter((msg) => msg.role === "assistant")
+    .reduce((sum, msg) => sum + (msg.cost ?? 0), 0)
+
+  const total = walk(id)
+
+  return { own, total, missing }
+}