fix(trajectory): show exact millisecond durations consistently

Drop the details-panel Duration toggle: Duration rows always show
integer milliseconds, matching the cell time column. Timeline labels
(Total/TTFT/Decoding) and step-group descriptions previously fell back
to second labels at or above one second; they now also show exact
milliseconds via the shared formatDurationMillis formatter.

packages/client/ui-trajectory/src/client/TrajectoryTable.tsx

@@ -299,26 +299,6 @@ function StartedAtValue({ timestamp }: { timestamp: number | null }) {
   )
 }
 
-function DurationValue({ seconds }: { seconds: number | null }) {
-  const [showMillis, setShowMillis] = useState(false)
-  if (seconds === null || !Number.isFinite(seconds)) return <dd>—</dd>
-  return (
-    <dd>
-      <button
-        type="button"
-        className={css.timestampToggle}
-        title={showMillis ? 'Show readable duration' : 'Show exact milliseconds'}
-        onClick={(event) => {
-          if (clickSelectsText(event.currentTarget)) return
-          setShowMillis(current => !current)
-        }}
-      >
-        {showMillis ? `${Math.round(seconds * 1000)} ms` : formatElapsedSeconds(seconds)}
-      </button>
-    </dd>
-  )
-}
-
 function totalTime(metrics: AssistantMetricDetail): string {
   if (!metrics.timingRecorded) return 'Not recorded'
   if (metrics.stepStartTime === null) return 'Step start unavailable'
@@ -1376,7 +1356,7 @@ function RecordTiming({ record }: { record: TableRecord }) {
     : (
       <dl className={css.overview}>
         <div><dt>Started</dt><StartedAtValue timestamp={record.cell.startedAt ?? null} /></div>
-        <div><dt>Duration</dt><DurationValue seconds={record.cell.timeSeconds} /></div>
+        <div><dt>Duration</dt><dd>{formatElapsedSeconds(record.cell.timeSeconds)}</dd></div>
         <div><dt>Timing source</dt><dd>{record.cell.timeSeconds === null ? 'Not available' : 'Session timestamps'}</dd></div>
       </dl>
     )
@@ -1399,7 +1379,7 @@ function RequestTiming({
     return (
       <dl className={css.overview}>
         <div><dt>Started</dt><StartedAtValue timestamp={request.startedAt} /></div>
-        <div><dt>Duration</dt><DurationValue seconds={duration} /></div>
+        <div><dt>Duration</dt><dd>{formatElapsedSeconds(duration)}</dd></div>
         <div>
           <dt>Timing source</dt>
           <dd>{duration === null ? 'Session timestamps (running)' : 'Session timestamps'}</dd>
@@ -1413,7 +1393,7 @@ function RequestTiming({
         <dt>Started</dt>
         <StartedAtValue timestamp={anchor?.cell.startedAt ?? null} />
       </div>
-      <div><dt>Duration</dt><DurationValue seconds={null} /></div>
+      <div><dt>Duration</dt><dd>{formatElapsedSeconds(null)}</dd></div>
     </dl>
   )
 }
@@ -2757,7 +2737,7 @@ export function TrajectoryTable({
                   </div>
                   <div>
                     <dt>Duration</dt>
-                    <DurationValue seconds={selected.cell.timeSeconds} />
+                    <dd>{formatElapsedSeconds(selected.cell.timeSeconds)}</dd>
                   </div>
                   <div>
                     <dt>Tokens</dt>
@@ -2872,7 +2852,7 @@ export function TrajectoryTable({
                   {(selected.cell.kind === 'user' || selected.cell.kind === 'context') && (
                     <div>
                       <dt>Duration</dt>
-                      <DurationValue seconds={selected.cell.timeSeconds} />
+                      <dd>{formatElapsedSeconds(selected.cell.timeSeconds)}</dd>
                     </div>
                   )}
                 </dl>

packages/client/ui-trajectory/src/client/timeline.ts

@@ -1,6 +1,7 @@
 /** Operation-sequence and recorded-time projections for the trajectory overview. */
 
 import type { TrajectoryTurnModel } from './layout.ts'
+import { formatDurationMillis } from './trajectory-record.ts'
 import type { TrajectoryCellKind, TrajectoryCellProps } from './trajectory-record.ts'
 
 /** Horizontal projection used by the trajectory timeline. */
@@ -34,14 +35,12 @@ export interface TrajectoryTimelineModel extends TrajectoryTimeRange {
 }
 
 /**
- * Format a timeline duration with a compact unit.
+ * Format a timeline duration as an integer-millisecond label.
  * @param milliseconds - Non-negative duration in milliseconds.
- * @returns Millisecond or second label.
+ * @returns Millisecond label with thousands separators.
  */
 export function formatTimelineOffset(milliseconds: number): string {
-  if (milliseconds < 1_000) return `${Math.round(milliseconds)} ms`
-  const seconds = milliseconds / 1_000
-  return seconds >= 10 ? `${Math.round(seconds)} s` : `${seconds.toFixed(1)} s`
+  return formatDurationMillis(milliseconds)
 }
 
 function laneFor(kind: TrajectoryCellKind): number {

packages/client/ui-trajectory/src/client/trajectory-record.ts

@@ -106,15 +106,20 @@ export function trajectoryRecordId(cell: TrajectoryCellProps): string {
 }
 
 /**
- * Format a duration with a precision that matches its magnitude.
+ * Format a duration in milliseconds with thousands separators.
+ * @param milliseconds - Duration in milliseconds, or `null` when absent.
+ * @returns `—` when unknown, otherwise an integer-millisecond label.
+ */
+export function formatDurationMillis(milliseconds: number | null): string {
+  if (milliseconds === null || !Number.isFinite(milliseconds)) return '—'
+  return `${Math.round(milliseconds).toLocaleString('en-US')} ms`
+}
+
+/**
+ * Format an elapsed duration given in seconds as a millisecond label.
  * @param seconds - Duration seconds, or `null` when absent.
- * @returns `—` when unknown, otherwise an integer-millisecond label
- * below one second and a tenth-of-a-second label at or above it.
+ * @returns `—` when unknown, otherwise an integer-millisecond label.
  */
 export function formatElapsedSeconds(seconds: number | null): string {
-  if (seconds === null || !Number.isFinite(seconds)) return '—'
-  if (seconds < 1) return `${Math.round(seconds * 1000)} ms`
-  const rounded = Math.round(seconds * 10) / 10
-  if (Number.isInteger(rounded)) return `${rounded} s`
-  return `${rounded.toFixed(1)} s`
+  return formatDurationMillis(seconds === null ? null : seconds * 1000)
 }