feat: show inline span durations in trace timeline (#1886)

## Summary

Adds duration labels next to each **span** bar in the trace waterfall timeline so users can read the duration at a glance without hovering the tooltip.

## Changes

### Timeline chart

- **TimelineChartRowEvents**
  - Renders a duration label (e.g. `12ms`, `1.2s`) **outside** each bar using `position: absolute`, so it doesn’t affect layout.
  - **Placement:** Label is on the **right** of the bar when most of the bar is before the timeline midpoint, and on the **left** when most of the bar is past the midpoint (based on bar center vs. `maxVal / 2`), to keep it in the emptier side.
  - Uses existing `renderMs()` from `TimelineChart/utils` for formatting.
  - Wraps each bar in a container with `overflow: visible` so the duration label is not clipped by the bar’s `text-truncate` (overflow hidden).
  - **TTimelineEvent** now supports optional `showDuration?: boolean`. When `false`, the duration label is hidden (default is to show).

### DBTraceWaterfallChart

- When building timeline events, sets `showDuration: type !== SourceKind.Log` so **log** rows do not show a duration (only spans do).

## Screenshots
<img width="1293" height="1187" alt="Screenshot 2026-03-11 at 18 36 34" src="https://github.com/user-attachments/assets/da04c317-a0bd-45d7-b0cc-f298564fb850" />


## Testing

- Open a trace with multiple spans and at least one correlated log; confirm duration appears beside span bars (left or right by midpoint) and does not appear beside log rows.

### References

- Closes HDX-3671

.changeset/olive-hounds-double.md

@@ -0,0 +1,5 @@
+---
+"@hyperdx/app": patch
+---
+
+feat: show inline span durations in trace timeline

packages/app/src/components/DBTraceWaterfallChart.tsx

@@ -820,6 +820,7 @@ export function DBTraceWaterfallChartContainer({
           minWidthPerc: 1,
           isError,
           markers,
+          showDuration: type !== SourceKind.Log,
         },
       ],
     };

packages/app/src/components/TimelineChart/TimelineChartRowEvents.tsx

@@ -5,6 +5,7 @@ import {
   TimelineSpanEventMarker,
   type TTimelineSpanEventMarker,
 } from './TimelineSpanEventMarker';
+import { renderMs } from './utils';
 
 export type TTimelineEvent = {
   id: string;
@@ -17,6 +18,7 @@ export type TTimelineEvent = {
   minWidthPerc?: number;
   isError?: boolean;
   markers?: TTimelineSpanEventMarker[];
+  showDuration?: boolean;
 };
 
 type TimelineChartRowProps = {
@@ -57,6 +59,12 @@ export const TimelineChartRowEvents = memo(function ({
         const percMarginLeft =
           scale * (((e.start - lastEventEnd) / maxVal) * 100);
 
+        const durationMs = e.end - e.start;
+        const barCenter = (e.start + e.end) / 2;
+        const timelineMidpoint = maxVal / 2;
+        // Duration on left when majority of bar is past halfway, otherwise on right
+        const durationOnRight = barCenter <= timelineMidpoint;
+
         return (
           <Tooltip
             key={e.id}
@@ -72,32 +80,60 @@ export const TimelineChartRowEvents = memo(function ({
             }}
           >
             <div
-              onMouseEnter={() => onEventHover?.(e.id)}
-              className="d-flex align-items-center h-100 cursor-pointer text-truncate hover-opacity"
               style={{
-                userSelect: 'none',
+                position: 'relative',
                 minWidth: `${percWidth.toFixed(6)}%`,
                 width: `${percWidth.toFixed(6)}%`,
                 marginLeft: `${percMarginLeft.toFixed(6)}%`,
-                position: 'relative',
-                borderRadius: 2,
-                fontSize: height * 0.5,
-                color: e.color,
-                backgroundColor: e.backgroundColor,
+                // overflow: 'visible',
               }}
             >
-              <div style={{ margin: 'auto' }} className="px-2">
-                {e.body}
+              <div
+                onMouseEnter={() => onEventHover?.(e.id)}
+                className="d-flex align-items-center h-100 cursor-pointer text-truncate hover-opacity"
+                style={{
+                  userSelect: 'none',
+                  width: '100%',
+                  position: 'relative',
+                  borderRadius: 2,
+                  fontSize: height * 0.5,
+                  color: e.color,
+                  backgroundColor: e.backgroundColor,
+                }}
+              >
+                <div style={{ margin: 'auto' }} className="px-2">
+                  {e.body}
+                </div>
+                {e.markers?.map((marker, idx) => (
+                  <TimelineSpanEventMarker
+                    key={`${e.id}-marker-${idx}`}
+                    marker={marker}
+                    eventStart={e.start}
+                    eventEnd={e.end}
+                    height={height}
+                  />
+                ))}
               </div>
-              {e.markers?.map((marker, idx) => (
-                <TimelineSpanEventMarker
-                  key={`${e.id}-marker-${idx}`}
-                  marker={marker}
-                  eventStart={e.start}
-                  eventEnd={e.end}
-                  height={height}
-                />
-              ))}
+              {!!e.showDuration && (
+                <span
+                  style={{
+                    position: 'absolute',
+                    top: 0,
+                    height: '100%',
+                    display: 'flex',
+                    alignItems: 'center',
+                    fontSize: height * 0.5,
+                    color: 'var(--color-text)',
+                    whiteSpace: 'nowrap',
+                    pointerEvents: 'none',
+                    ...(durationOnRight
+                      ? { left: '100%', marginLeft: 4 }
+                      : { right: '100%', marginRight: 4 }),
+                  }}
+                >
+                  {renderMs(durationMs)}
+                </span>
+              )}
             </div>
           </Tooltip>
         );

packages/app/src/components/TimelineChart/__tests__/utils.test.ts

@@ -1,10 +1,6 @@
 import { calculateInterval, renderMs } from '../utils';
 
 describe('renderMs', () => {
-  it('returns "0ms" for 0', () => {
-    expect(renderMs(0)).toBe('0ms');
-  });
-
   it('formats sub-second values as ms', () => {
     expect(renderMs(500)).toBe('500ms');
     expect(renderMs(999)).toBe('999ms');
@@ -25,6 +21,26 @@ describe('renderMs', () => {
     expect(renderMs(1500)).toBe('1.500s');
     expect(renderMs(1234.567)).toBe('1.235s');
   });
+
+  it('returns "0µs" for 0', () => {
+    expect(renderMs(0)).toBe('0µs');
+  });
+
+  it('formats sub-millisecond values as µs', () => {
+    expect(renderMs(0.001)).toBe('1µs');
+    expect(renderMs(0.5)).toBe('500µs');
+    expect(renderMs(0.999)).toBe('999µs');
+  });
+
+  it('rounds sub-millisecond values to nearest µs', () => {
+    expect(renderMs(0.0005)).toBe('1µs');
+    expect(renderMs(0.9994)).toBe('999µs');
+  });
+
+  it('falls through to ms when µs rounds to 1000', () => {
+    // 0.9995ms rounds to 1000µs, so it should render as 1ms instead
+    expect(renderMs(0.9995)).toBe('1ms');
+  });
 });
 
 describe('calculateInterval', () => {

packages/app/src/components/TimelineChart/utils.ts

@@ -1,4 +1,12 @@
 export function renderMs(ms: number) {
+  if (ms < 1) {
+    const µsRounded = Math.round(ms * 1000);
+
+    if (µsRounded !== 1000) {
+      return `${µsRounded}µs`;
+    }
+  }
+
   if (ms < 1000) {
     return `${Math.round(ms)}ms`;
   }