fix(client): count only the sessions each KPI figure covers

The cost cell's sub-line now counts the sessions whose spend the price
book could estimate (costSessions), and the cache-hit cell's the
sessions whose usage feeds the rate (usageSessions) — a session with
usage but no book rates feeds the rate while pricing to nothing, and a
session without usage counts toward neither figure.

src/client/components/overviewPanel.tsx

@@ -150,12 +150,12 @@ export function makeOverviewPanel(ctx: ClientCtx, kit: ViewKit): (props: Overvie
                   <div className="lc-stat lc-ov-kpi">
                     <span className="lc-stat-label">{t('stats.cost')}</span>
                     <span className="lc-stat-value">{kpi.cost === null ? '—' : formatCost(kpi.cost, currency)}</span>
-                    <span className="lc-stat-sub">{t('ov.kpi.sessionsSub', { n: kpi.sessions })}</span>
+                    <span className="lc-stat-sub">{t('ov.kpi.sessionsSub', { n: kpi.costSessions })}</span>
                   </div>
                   <div className="lc-stat lc-ov-kpi">
                     <span className="lc-stat-label">{t('stats.cacheHit')}</span>
                     <span className="lc-stat-value">{kpi.cacheHit === null ? '—' : kpi.cacheHit + '%'}</span>
-                    <span className="lc-stat-sub">{t('ov.kpi.sessionsSub', { n: kpi.sessions })}</span>
+                    <span className="lc-stat-sub">{t('ov.kpi.sessionsSub', { n: kpi.usageSessions })}</span>
                   </div>
                   <div className="lc-stat lc-ov-kpi">
                     <span className="lc-stat-label">{t('stats.toolCalls')}</span>

src/client/overview.ts

@@ -392,8 +392,12 @@ export interface OverviewKpis {
   turns: number
   /** Estimated spend in the display currency (null: nothing priced). */
   cost: number | null
+  /** Sessions whose spend the book could price (the cost cell's sub-line). */
+  costSessions: number
   /** Cache-hit share of billed input, truncated (null: nothing billed). */
   cacheHit: string | null
+  /** Sessions whose usage feeds the cache-hit rate (the cache-hit cell's sub-line). */
+  usageSessions: number
   /** Their completed tool calls. */
   toolCalls: number
   /** Their summed tool-run time (the tool-calls cell's sub-line). */
@@ -417,7 +421,15 @@ export function kpisOf(
   let toolsMs = 0
   let calls = 0
   let wallMs = 0
+  let costSessions = 0
+  let usageSessions = 0
   for (const row of rows) {
+    const cost = row.timeline?.cost
+    // Each qualifying sub-line counts the sessions its own figure covers: a
+    // session with usage but no book rates feeds the cache-hit rate while
+    // pricing to nothing.
+    if (estimateSessionCost(cost, prices, currency) !== null) costSessions++
+    if (usageTotalsOf(cost) !== null) usageSessions++
     turns += turnsOf(row.timeline)
     const timing = row.timeline?.timing
     toolCalls += timing?.toolCalls ?? 0
@@ -431,7 +443,9 @@ export function kpisOf(
     tokens: totals?.total ?? 0,
     turns,
     cost: estimateSessionCost(usage, prices, currency),
+    costSessions,
     cacheHit: totals === null ? null : cacheHitPercent(totals.cacheRead, totals.input + totals.cacheRead + totals.cacheWrite),
+    usageSessions,
     toolCalls,
     toolsMs,
     calls,

tests/client/components/overviewPanel.spec.ts

@@ -139,9 +139,10 @@ describe('OverviewPanel', () => {
     assert.equal(values[5], '3m0s')
     assert.ok(text(m.container).includes('tool runs 40.0s'), 'the tool calls cell qualifies with the summed run time')
     assert.ok(text(m.container).includes('8 model calls'), 'the active-time cell qualifies with the model-call count')
-    // Cost and cache hit qualify with the session count they aggregate over.
+    // Cost and cache hit qualify with the session count each figure covers
+    // (only session a carries usage; b folds no cost at all).
     const subs = queryAll(m.container, '.lc-stat-sub').map(el => el.textContent)
-    assert.deepEqual(subs.slice(2, 4), ['across 2 sessions', 'across 2 sessions'])
+    assert.deepEqual(subs.slice(2, 4), ['across 1 sessions', 'across 1 sessions'])
     // Heatmap drew cells for the two ledger days.
     assert.ok(queryAll(m.container, 'button.lc-heat-cell').length >= 2)
     // Cards: a (current, running, grouped), b, and c is outside the 30d range.

tests/client/overview.spec.ts

@@ -348,18 +348,39 @@ describe('kpisOf', () => {
     assert.equal(kpi.turns, 5)
     assert.ok(kpi.cost !== null && Math.abs(kpi.cost - 195e-6) < 1e-12, '50×0.1 + 100×1 + 10×1 + 40×2 per 1M')
     assert.equal(kpi.cacheHit, '31.25', '50 reads of 160 billed input, truncated')
+    assert.equal(kpi.costSessions, 1, 'only the priced session counts toward the cost cell')
+    assert.equal(kpi.usageSessions, 1, 'only the billed session feeds the cache-hit rate')
     assert.equal(kpi.toolCalls, 7, 'tool calls sum across rows')
     assert.equal(kpi.toolsMs, 20_000)
     assert.equal(kpi.calls, 6)
     assert.equal(kpi.wallMs, 120_000)
   })
 
+  test('a session with usage the book cannot price feeds the cache-hit rate but prices to nothing', () => {
+    const rows = [
+      rowOf({ timeline: { cost: COST, requests: [] } as unknown as ContextTimeline }),
+      rowOf({
+        timeline: {
+          cost: { openai: { 'gpt-5': { peak: { uncached: 10, cacheRead: 5, cacheWrite: 1, output: 2 } } } },
+          requests: [],
+        } as unknown as ContextTimeline,
+      }),
+      rowOf(),
+    ]
+    const kpi = kpisOf(rows, 3, prices, 'usd')
+    assert.equal(kpi.costSessions, 1, 'only the priced session counts toward the cost cell')
+    assert.equal(kpi.usageSessions, 2, 'both billed sessions feed the cache-hit rate')
+    assert.ok(kpi.cost !== null && Math.abs(kpi.cost - 195e-6) < 1e-12, 'the unpriced session adds nothing to the estimate')
+  })
+
   test('an unbilled set zeroes and dashes', () => {
     const kpi = kpisOf([rowOf()], 1, null, 'cny')
     assert.equal(kpi.tokens, 0)
     assert.equal(kpi.turns, 0)
     assert.equal(kpi.cost, null)
     assert.equal(kpi.cacheHit, null)
+    assert.equal(kpi.costSessions, 0)
+    assert.equal(kpi.usageSessions, 0)
     assert.equal(kpi.toolCalls, 0, 'no timing folds to zeroed tools and time')
     assert.equal(kpi.toolsMs, 0)
     assert.equal(kpi.calls, 0)