review: address ds-review-bot findings on session-stats

- stateVersion starts at 1: the package is new, no persisted rows predate it
- pendingCalls pairs by own key so a provider callId naming a prototype
  property cannot fold toolMs to NaN on an unmatched crash-recovery result
- StatsLine folds the window fallback only when no sessionStats value is
  served, and gates the token group on actual token activity instead of
  steps, so failed-only sessions drop the zero-token group
- correct the crash-step counting semantics in the README and Agent Note:
  recovery closes interrupted steps with a synthetic step/end on reload
- reword the window-scoped alternative as a plain rejected option and name
  isTokenDelta's home beside the StreamChunk type

packages/client/runtime/src/client/sessions/assistant-timing.ts

@@ -6,7 +6,7 @@ import { isTokenDelta } from '@deepseek-ai/dsh-llm/message'
 import type { SessionEvent } from '@deepseek-ai/dsh-session/types'
 import type { AssistantTiming } from './conversation.ts'
 
-// The first-token predicate lives with the StreamChunk vocabulary in dsh-llm;
+// The first-token predicate lives beside the StreamChunk type in dsh-llm;
 // re-exported here so Chat Definitions keep their client-runtime import.
 export { isTokenDelta } from '@deepseek-ai/dsh-llm/message'
 

packages/client/ui-conversation/src/client/chat/StatsLine.tsx

@@ -162,12 +162,13 @@ export interface StatsLineProps {
 
 export const StatsLine = memo(function StatsLine({ useSession, useProjection, t }: StatsLineProps) {
   const settledNodes = useSession(s => s.chat.legacy.nodes)
-  const windowStats = useMemo(() => deriveStats(settledNodes), [settledNodes])
   const usage = useProjection('tokenUsage')
   // Every figure rides the durable sessionStats projection, so paging and
   // compaction cannot change any of them; an assembly without the unit falls
-  // back to the window-scoped fold wholesale (same field names).
-  const stats = useProjection('sessionStats') ?? windowStats
+  // back to the window-scoped fold wholesale (same field names), paid only
+  // while no projection value is served.
+  const projected = useProjection('sessionStats')
+  const stats = useMemo(() => projected ?? deriveStats(settledNodes), [projected, settledNodes])
   // Pipe-separated groups (figma stats strip); a group with no data drops out whole.
   const groups: string[] = []
   if (stats.steps > 0) {
@@ -190,9 +191,11 @@ export const StatsLine = memo(function StatsLine({ useSession, useProjection, t
   // Context occupancy deliberately lives on the composer's ContextMeter ring,
   // not here — one home per fact.
   // Billing rides the durable projection, so these survive paging and
-  // compaction. Suppress the empty projection on a brand-new session.
+  // compaction. Gated on actual token activity: a session whose steps all
+  // settled without billing (e.g. every request failed) shows its counts
+  // without a zero-token group.
   if (usage !== undefined
-    && (stats.steps > 0 || billedInputTokens(usage) > 0 || usage.outputTokens > 0)) {
+    && (billedInputTokens(usage) > 0 || usage.outputTokens > 0)) {
     const cacheHit = cacheHitPercent(usage)
     if (cacheHit !== null) groups.push(t('stats.cacheHit', { percent: cacheHit }))
     groups.push(t('stats.tokens', {

packages/client/ui-conversation/tests/chat-stats.client.spec.tsx

@@ -314,6 +314,17 @@ describe('StatsLine', () => {
     expect(view.container.textContent).toBe('')
   })
 
+  it('hides the zero-token group when steps closed without any billed activity', () => {
+    // A session whose only turn failed before billing (e.g. an auth error):
+    // the counts group renders alone, not an uninformative zero-token group.
+    const { source } = makeSource()
+    const view = render(<StatsLine {...props(source, {
+      tokenUsage: { uncachedInputTokens: 0, outputTokens: 0, cacheReadTokens: 0, cacheWriteTokens: 0 },
+      sessionStats: sessionStats({ turns: 1, steps: 1 }),
+    })} />)
+    expect(view.container.textContent).toBe('1 turns · 1 steps')
+  })
+
   it('keeps the counts group over an empty visible window when the projection carries totals', () => {
     // Extends the durable-groups guarantee: full-session counts survive a
     // window that compaction (or paging) left without assistant nodes.