Live session cost in the connect footer (cost_millicents on status/done frames)

src/commands/connect.ts

@@ -3,7 +3,7 @@ import React from 'react'
 import { render } from 'ink'
 import { ApiClient } from '../lib/api'
 import { requireToken, resolveApiBase, resolveAppBase } from '../lib/config'
-import { runAction } from '../lib/output'
+import { runAction, usdNumberFromMillicents } from '../lib/output'
 import { foldCosts, isConnectVisibleRecord, recordToItems, type CCEvent } from '../lib/events'
 import { sessionUrl } from '../lib/urls'
 import { resolveWsBase } from '../lib/ws'
@@ -122,6 +122,11 @@ export async function runConnect(
         .flatMap((st) => recordToItems(st, `s${st.feed_seq}`))
     : []
   const initialCost = foldCosts(ordered.map((st) => st.payload as CCEvent))
+  // The server's ledger total at connect time; live updates arrive as
+  // cost_millicents on status/done frames.
+  const initialServerCostUsd = usdNumberFromMillicents(
+    session.cost_tokens + session.cost_sandbox_cpu + session.cost_sandbox_memory + session.cost_fee,
+  )
 
   // Written by the app when it exits because the conversation closed (terminal;
   // nothing left to reconnect to), so the detach sign-off below stays honest.
@@ -140,6 +145,7 @@ export async function runConnect(
       initialStatus: session.surface?.status ?? session.status,
       sessionUrl: url,
       initialCost,
+      initialServerCostUsd,
       initialNotice: reason ?? null,
       // The session's one model, fixed at creation (backend tokens_model).
       model: typeof session.tokens_model === 'string' ? session.tokens_model : null,

src/lib/output.ts

@@ -57,6 +57,12 @@ export function usdFromMillicents(millicents: number): string {
   return `$${(millicents / 100_000).toFixed(2)}`
 }
 
+// Millicents -> USD as a number, for callers that do math/compare before
+// formatting (e.g. the connect footer's monotonic live cost).
+export function usdNumberFromMillicents(millicents: number): number {
+  return millicents / 100_000
+}
+
 export function usd(amount: number): string {
   return `$${amount.toFixed(2)}`
 }

src/lib/ws.ts

@@ -4,14 +4,17 @@ import { DEFAULT_WS_BASE, USER_AGENT } from './constants'
 
 // The frame protocol spoken over the session WebSocket (server -> client). One
 // JSON object per message. Mirrors session_stream.py in the backend.
-//   status: { type, status, session, run, ts }
+//   status: { type, status, session, run, cost_millicents, ts }
 //   stdout/stderr: { type, data, seq, ts }
 //   delta:  { type, text?, output_tokens? }
-//   done: { type, status, session, run, exit_status }
+//   done: { type, status, session, run, exit_status, cost_millicents }
 //   error: { type, message }
 // `status` is the derived single word (working/waiting/sleeping/starting/…);
 // `session` (alive/sleeping/closed) and `run` are the two raw axes. All three
 // are null for an un-keyed (laptop) session. See session_surface.py.
+// `cost_millicents` is the session's running total cost from the server's spend
+// ledger — the billing authority; it climbs mid-turn as the agent spends, and
+// the server emits a status frame on every change (absent on older backends).
 // `seq` is a monotonic per-session cursor; the client resumes from the last seq
 // it saw via `?after_seq=` so a dropped socket loses nothing. `delta` is the
 // EPHEMERAL live-streaming frame (partial assistant text + running token count);
@@ -24,6 +27,8 @@ export interface StreamFrame {
   // status/done frames: the two raw session-surface axes (null for laptop).
   session?: string | null
   run?: string | null
+  // status/done frames: the session's running total cost (millicents).
+  cost_millicents?: number
   seq?: number
   ts?: string
   message?: string

src/ui/ConnectApp.tsx

@@ -17,6 +17,7 @@ import {
   type TranscriptItem,
 } from '../lib/events'
 import { hyperlink } from '../lib/urls'
+import { usdNumberFromMillicents } from '../lib/output'
 import { VERSION } from '../lib/constants'
 
 // The interactive `agent session connect` UI, modelled on Claude Code: a
@@ -54,6 +55,10 @@ export interface ConnectAppProps {
   sessionUrl: string
   // Spend seeded from the stored steps: cumulative total + the last turn's cost.
   initialCost: { total: number | null; lastStep: number | null }
+  // The server-reported session total (USD) at connect time, from the session's
+  // cost columns — the billing authority. Live updates arrive as
+  // `cost_millicents` on status/done frames; null against older backends.
+  initialServerCostUsd?: number | null
   // A one-line caveat shown as the app's opening notice (e.g. "watch-only:
   // this conversation is closed"). null for the normal connect.
   initialNotice?: string | null
@@ -132,6 +137,15 @@ export function ConnectApp(props: ConnectAppProps): React.ReactElement {
   // the latest Claude Code result; `lastStep` is the cost of the most recent
   // turn (the delta between the last two results).
   const [cost, setCost] = useState(props.initialCost)
+  // The server's authoritative running total (USD), from `cost_millicents` on
+  // status/done frames (and the status poll as backstop). Preferred over the
+  // CC-derived total when present; kept monotonic so the footer never dips.
+  const [serverCostUsd, setServerCostUsd] = useState<number | null>(
+    props.initialServerCostUsd ?? null,
+  )
+  const applyServerCostUsd = useCallback((usd: number): void => {
+    setServerCostUsd((prev) => (prev == null ? usd : Math.max(prev, usd)))
+  }, [])
 
   // Live-flow state that must survive re-renders without triggering them.
   const afterSeq = useRef(0)
@@ -305,6 +319,15 @@ export function ConnectApp(props: ConnectAppProps): React.ReactElement {
   const handleFrame = useCallback(
     (frame: StreamFrame): void => {
       if (typeof frame.seq === 'number') afterSeq.current = Math.max(afterSeq.current, frame.seq)
+      // status/done frames carry the server's running session total; the
+      // server emits a status frame on every cost change, so the footer's
+      // dollar figure climbs mid-turn as the agent spends.
+      if (
+        (frame.type === 'status' || frame.type === 'done') &&
+        typeof frame.cost_millicents === 'number'
+      ) {
+        applyServerCostUsd(usdNumberFromMillicents(frame.cost_millicents))
+      }
       if (frame.type === 'status' && frame.status && frame.status !== lastStatus.current) {
         lastStatus.current = frame.status
         setStatus(frame.status)
@@ -331,7 +354,7 @@ export function ConnectApp(props: ConnectAppProps): React.ReactElement {
       }
       scheduleRefresh()
     },
-    [finishClosed, scheduleRefresh],
+    [applyServerCostUsd, finishClosed, scheduleRefresh],
   )
 
   // Keep the socket attached across reconnects/resume. A keyed session going
@@ -406,6 +429,13 @@ export function ConnectApp(props: ConnectAppProps): React.ReactElement {
   const pollStatus = useCallback(async (): Promise<void> => {
     try {
       const s = await api.getAgentSession(sessionId)
+      // Same figure the stream's cost_millicents carries, so the footer keeps
+      // climbing even when the socket never attached (polling fallback).
+      applyServerCostUsd(
+        usdNumberFromMillicents(
+          s.cost_tokens + s.cost_sandbox_cpu + s.cost_sandbox_memory + s.cost_fee,
+        ),
+      )
       const word = s.surface?.status ?? s.status
       if (word !== lastStatus.current) {
         lastStatus.current = word
@@ -417,7 +447,7 @@ export function ConnectApp(props: ConnectAppProps): React.ReactElement {
     } catch {
       // Transient fetch failure — the next tick retries.
     }
-  }, [api, finishClosed, sessionId])
+  }, [api, applyServerCostUsd, finishClosed, sessionId])
 
   useEffect(() => {
     pump()
@@ -595,8 +625,11 @@ export function ConnectApp(props: ConnectAppProps): React.ReactElement {
 
   // The persistent footer status line, kept minimal: the current status and
   // the running spend (cumulative total + the last turn's cost). Session
-  // identity lives in the banner; command hints live in --help.
-  const totalStr = `$${(cost.total ?? 0).toFixed(2)}`
+  // identity lives in the banner; command hints live in --help. The total
+  // prefers the server's ledger figure (live via cost_millicents frames,
+  // climbing mid-turn); the CC-derived result total is the fallback against
+  // older backends.
+  const totalStr = `$${(serverCostUsd ?? cost.total ?? 0).toFixed(2)}`
   const lastStepStr = cost.lastStep != null ? ` (Last step: $${cost.lastStep.toFixed(2)})` : ''
   const metaLine = `${status} · ${totalStr} total${lastStepStr}`
   // Three distinct, factual activity signals — never whimsy. All render IN the

test/output.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest'
-import { relativeAge, usd, usdFromMillicents } from '../src/lib/output'
+import { relativeAge, usd, usdFromMillicents, usdNumberFromMillicents } from '../src/lib/output'
 
 describe('usdFromMillicents', () => {
   it('converts millicents to dollars (1 cent = 1000 millicents)', () => {
@@ -9,6 +9,14 @@ describe('usdFromMillicents', () => {
   })
 })
 
+describe('usdNumberFromMillicents', () => {
+  it('converts millicents to a USD number for math before formatting', () => {
+    expect(usdNumberFromMillicents(0)).toBe(0)
+    expect(usdNumberFromMillicents(100_000)).toBe(1)
+    expect(usdNumberFromMillicents(12_345_000)).toBeCloseTo(123.45)
+  })
+})
+
 describe('relativeAge', () => {
   const now = new Date('2026-07-06T12:00:00Z')