---
id: S03
parent: M004
milestone: M004
provides:
  - Technique detail API returns video_filename on each key moment
  - Technique page renders meta stats, video sources, and signal chain flow blocks matching reference layout
requires:
  - slice: S01
    provides: Fixed technique detail endpoint (422 bug resolved)
affects:
  - S04
key_files:
  - backend/schemas.py
  - backend/routers/techniques.py
  - frontend/src/api/public-client.ts
  - frontend/src/pages/TechniquePage.tsx
  - frontend/src/App.css
key_decisions:
  - Populate video_filename via post-processing loop rather than Pydantic from_attributes auto-mapping, since the field comes from a joined relation not a direct column
  - Used text-overflow ellipsis on video filename with max-width 20rem to prevent layout breakage on long filenames
patterns_established:
  - Chained selectinload for cross-relation field population in technique detail endpoint — pattern for adding more joined fields to API responses
observability_surfaces:
  - none
drill_down_paths:
  - .gsd/milestones/M004/slices/S03/tasks/T01-SUMMARY.md
  - .gsd/milestones/M004/slices/S03/tasks/T02-SUMMARY.md
duration: ""
verification_result: passed
completed_at: 2026-03-30T06:58:43.576Z
blocker_discovered: false
---

# S03: Technique Page Redesign + Video Source on Moments

**Technique detail pages now show meta stats, video filenames on key moments, and monospace signal chain flow blocks with arrow separators — matching the reference layout spec.**

## What Happened

This slice delivered three visual changes to the technique page plus the backend data prerequisite to power them.

**T01 (Backend):** Added `video_filename: str = ""` to the `KeyMomentSummary` Pydantic schema. Chained `.selectinload(KeyMoment.source_video)` onto the existing key_moments eager load in the technique detail endpoint. Added a post-processing loop that populates `video_filename` from the joined `source_video.filename` relation. Deployed to ub01 and verified all 13 key moments on the wave-shaping technique page return populated video filenames.

**T02 (Frontend):** Three changes to TechniquePage.tsx plus corresponding CSS:
1. **Meta stats line** below the title — shows source count (unique video filenames), moment count, and last-updated date. Computed inline via an IIFE for readability.
2. **Video filename on key moments** — each moment row displays the source video filename in muted monospace text, truncated with ellipsis at 20rem to prevent layout breakage.
3. **Signal chain flow blocks** — replaced the numbered `<ol>` list with a horizontal-wrap monospace `<div>` where steps are separated by cyan arrow (`→`) separators. Uses `var(--color-accent)` for the arrows, `var(--color-bg-surface)` background, and proper border-radius.

All CSS uses `var(--*)` tokens exclusively — zero hardcoded hex colors outside `:root`. The TypeScript `KeyMomentSummary` interface was updated to include `video_filename: string`. Build passes cleanly with zero errors.

## Verification

1. API returns video_filename on all key moments: `curl` to wave-shaping technique endpoint → 13 moments, all with `video_filename` populated as "Skope - Understanding Waveshapers (2160p).mp4".
2. Frontend builds cleanly: `npm run build` exits 0 with zero TypeScript errors.
3. No hardcoded colors: grep for hex colors outside `:root` returns zero matches.
4. Live deployment on ub01:8096 serves the updated frontend with all three visual changes rendering correctly.

## Requirements Advanced

- R006 — Technique page now renders meta stats line, video source filenames on key moments, and signal chain flow blocks with arrow separators — matching the reference layout specification

## Requirements Validated

None.

## New Requirements Surfaced

None.

## Requirements Invalidated or Re-scoped

None.

## Deviations

None.

## Known Limitations

The meta stats line computes source count client-side from video filenames — if two videos have the same filename (different paths), they'd be counted as one source. Unlikely in practice.

## Follow-ups

None.

## Files Created/Modified

- `backend/schemas.py` — Added video_filename: str = '' to KeyMomentSummary schema
- `backend/routers/techniques.py` — Chained selectinload for source_video; post-processing loop populates video_filename
- `frontend/src/api/public-client.ts` — Added video_filename: string to KeyMomentSummary TypeScript interface
- `frontend/src/pages/TechniquePage.tsx` — Added meta stats line, video filename display on moments, monospace signal chain flow blocks
- `frontend/src/App.css` — Added CSS for technique-header__stats, technique-moment__source, technique-chain__flow/arrow/step classes
