fix(tui): total root session family cost

packages/tui/src/component/prompt/index.tsx

@@ -290,7 +290,7 @@ export function Prompt(props: PromptProps) {
       .list(session.location)
       ?.find((model) => model.providerID === last.model.providerID && model.id === last.model.id)
     const pct = model?.limit.context ? `${Math.round((tokens / model.limit.context) * 100)}%` : undefined
-    const cost = session.cost
+    const cost = data.session.cost(props.sessionID)
     return {
       context: pct ? `${Locale.number(tokens)} (${pct})` : Locale.number(tokens),
       cost: cost > 0 ? money.format(cost) : undefined,

packages/tui/src/context/data.tsx

@@ -805,6 +805,15 @@ export const { use: useData, provider: DataProvider } = createSimpleContext({
         family(sessionID: string) {
           return store.session.family[resolveRoot(sessionID)] ?? []
         },
+        cost(sessionID: string) {
+          const session = store.session.info[sessionID]
+          if (!session) return 0
+          if (session.parentID) return session.cost
+          return (store.session.family[sessionID] ?? [sessionID]).reduce(
+            (total, id) => total + (store.session.info[id]?.cost ?? 0),
+            0,
+          )
+        },
         status(sessionID: string) {
           return store.session.status[sessionID] ?? "idle"
         },

packages/tui/src/feature-plugins/sidebar/context.tsx

@@ -16,7 +16,7 @@ function View(props: { api: TuiPluginApi; session_id: string }) {
   const theme = () => props.api.theme.current
   const msg = createMemo(() => data.session.message.list(props.session_id))
   const session = createMemo(() => data.session.get(props.session_id))
-  const cost = createMemo(() => session()?.cost ?? 0)
+  const cost = createMemo(() => data.session.cost(props.session_id))
 
   const state = createMemo(() => {
     const last = lastAssistantWithUsage(msg(), session()?.revert?.messageID)

packages/tui/src/routes/session/subagent-footer.tsx

@@ -33,7 +33,7 @@ export function SubagentFooter() {
       .model.list(current.location)
       ?.find((model) => model.providerID === last.model.providerID && model.id === last.model.id)
     const pct = model?.limit.context ? `${Math.round((tokens / model.limit.context) * 100)}%` : undefined
-    const cost = current.cost
+    const cost = data.session.cost(route.sessionID)
 
     const money = new Intl.NumberFormat("en-US", {
       style: "currency",

packages/tui/test/cli/tui/data.test.tsx

@@ -2148,12 +2148,12 @@ test("projects live instruction updates with their message ID", async () => {
   }
 })
 
-function sessionInfo(id: string, parentID: string | undefined) {
+function sessionInfo(id: string, parentID: string | undefined, cost = 0) {
   return {
     id,
     parentID,
     projectID: "proj_test",
-    cost: 0,
+    cost,
     tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
     time: { created: 0, updated: 0 },
     title: id,
@@ -2164,10 +2164,11 @@ function sessionInfo(id: string, parentID: string | undefined) {
 // Mounts a DataProvider whose `/api/session/:id` responses are driven by the
 // given parent map (sessionID -> parentID). Roots omit the entry. Reused across
 // the family-index tests below.
-async function mountData(parents: Record<string, string>) {
+async function mountData(parents: Record<string, string>, costs: Record<string, number> = {}) {
   const calls = createFetch((url) => {
     const match = url.pathname.match(/^\/api\/session\/([^/]+)$/)
-    if (match && match[1] !== "active") return json({ data: sessionInfo(match[1], parents[match[1]]) })
+    if (match && match[1] !== "active")
+      return json({ data: sessionInfo(match[1], parents[match[1]], costs[match[1]]) })
   })
   let data!: ReturnType<typeof useData>
   let ready!: () => void
@@ -2235,6 +2236,24 @@ test("indexes arbitrarily deep nesting under a single root", async () => {
   }
 })
 
+test("totals family cost for roots and keeps subagent cost scoped", async () => {
+  const { data, app } = await mountData(
+    { grandchild: "child", child: "root" },
+    { root: 1, child: 2, grandchild: 3 },
+  )
+  try {
+    await data.session.refresh("grandchild")
+    await data.session.refresh("child")
+    await data.session.refresh("root")
+
+    expect(data.session.cost("root")).toBe(6)
+    expect(data.session.cost("child")).toBe(2)
+    expect(data.session.cost("grandchild")).toBe(3)
+  } finally {
+    app.renderer.destroy()
+  }
+})
+
 test("re-registering an existing session is idempotent", async () => {
   const { data, app } = await mountData({ grandchild: "child", child: "root" })
   try {