---
id: T03
parent: S01
milestone: M020
provides: []
requires: []
affects: []
key_files: ["frontend/src/api/videos.ts", "frontend/src/components/TranscriptSidebar.tsx", "frontend/src/pages/WatchPage.tsx", "frontend/src/App.tsx", "frontend/src/pages/TechniquePage.tsx", "frontend/src/App.css"]
key_decisions: ["TranscriptSidebar uses button elements for segments — semantic click targets with keyboard accessibility", "Transcript fetch failure is non-blocking — player works without sidebar"]
patterns_established: []
drill_down_paths: []
observability_surfaces: []
duration: ""
verification_result: "npx tsc --noEmit: zero type errors. npm run build: clean build, WatchPage code-split into separate chunk (10.71 KB)."
completed_at: 2026-04-03T23:49:51.368Z
blocker_discovered: false
---

# T03: Built WatchPage with video player, synced transcript sidebar, lazy-loaded /watch/:videoId route, and clickable timestamp links on TechniquePage key moments

> Built WatchPage with video player, synced transcript sidebar, lazy-loaded /watch/:videoId route, and clickable timestamp links on TechniquePage key moments

## What Happened
---
id: T03
parent: S01
milestone: M020
key_files:
  - frontend/src/api/videos.ts
  - frontend/src/components/TranscriptSidebar.tsx
  - frontend/src/pages/WatchPage.tsx
  - frontend/src/App.tsx
  - frontend/src/pages/TechniquePage.tsx
  - frontend/src/App.css
key_decisions:
  - TranscriptSidebar uses button elements for segments — semantic click targets with keyboard accessibility
  - Transcript fetch failure is non-blocking — player works without sidebar
duration: ""
verification_result: passed
completed_at: 2026-04-03T23:49:51.368Z
blocker_discovered: false
---

# T03: Built WatchPage with video player, synced transcript sidebar, lazy-loaded /watch/:videoId route, and clickable timestamp links on TechniquePage key moments

**Built WatchPage with video player, synced transcript sidebar, lazy-loaded /watch/:videoId route, and clickable timestamp links on TechniquePage key moments**

## What Happened

Created API client (videos.ts) with TypeScript interfaces for VideoDetail and TranscriptSegment. Built TranscriptSidebar with O(log n) binary search for active segment, auto-scroll, and click-to-seek. Composed WatchPage with useMediaSync, VideoPlayer, PlayerControls, and TranscriptSidebar — transcript fetch failure is non-blocking. Added lazy-loaded route in App.tsx and updated TechniquePage to wrap key moment timestamps in Links to /watch/:videoId?t=X. Added responsive CSS grid layout (sidebar beside player on desktop, below on mobile).

## Verification

npx tsc --noEmit: zero type errors. npm run build: clean build, WatchPage code-split into separate chunk (10.71 KB).

## Verification Evidence

| # | Command | Exit Code | Verdict | Duration |
|---|---------|-----------|---------|----------|
| 1 | `cd frontend && npx tsc --noEmit` | 0 | ✅ pass | 2800ms |
| 2 | `cd frontend && npm run build` | 0 | ✅ pass | 4700ms |


## Deviations

Fixed TS2532 strict array indexing in binary search — tsc -b mode is stricter than --noEmit.

## Known Issues

None.

## Files Created/Modified

- `frontend/src/api/videos.ts`
- `frontend/src/components/TranscriptSidebar.tsx`
- `frontend/src/pages/WatchPage.tsx`
- `frontend/src/App.tsx`
- `frontend/src/pages/TechniquePage.tsx`
- `frontend/src/App.css`


## Deviations
Fixed TS2532 strict array indexing in binary search — tsc -b mode is stricter than --noEmit.

## Known Issues
None.
