---
id: CE-WP-0003
type: workplan
title: "Form binding + visual guide — EvidenceLink, rect registry, SVG overlay"
domain: citation_evidence
repo: citation-evidence
repo_id: a677c189-b4e2-4f2a-9e48-faa482c277e6
topic_slug: citation_evidence_mvp
topic_id: 96fa8e80-9f74-40f2-84cd-644e9747b9ec
state_hub_workstream_id: 7b5b7235-57e3-4835-8fa6-376bb518fe2d
status: done
owner: Bernd
created: 2026-05-24
updated: 2026-05-25
depends_on_workplan: CE-WP-0002
spec_refs:
  - wiki/ProductRequirementsDocument.md
  - wiki/ArchitectureOverview.md
  - wiki/SharedContracts.md
---

# CE-WP-0003 — Form Binding + Visual Guide

Build the evidence-backed form mode and the SVG visual guide overlay.
After this workplan, a user can:

1. Open a form next to the document viewer.
2. Drag (or click-to-link) an evidence item from the sidebar onto a form
   field.
3. Click a form field → its linked evidence items appear → the active
   evidence's source passage is scrolled into view and highlighted → an SVG
   guide visually connects the field, the evidence card, and the highlight.
4. Cycle through multiple evidence items on the same field.

This is the workplan that stress-tests the rect-registry contract from
`wiki/SharedContracts.md` §7. The form, the evidence card, and the viewer's
highlight all need to publish rects to a single overlay that re-renders on
scroll/resize/focus.

## Dependency Order

```
T01 (EvidenceLink + EvidenceSet types + relation/status enums)
  └─ T02 (binding service + in-memory link repo + active-state machine)
       └─ T03 (rect registry — the contract from SharedContracts.md §7)
            └─ T04 (form schema + simple field renderer)
                 └─ T05 (side-by-side layout + drag-or-click to link)
                      └─ T06 (active-evidence cycling on a field)
                           └─ T07 (SVG visual guide overlay)
                                └─ T08 (E2E test of PRD scenario steps 5-9)
```

---

## T01 — `EvidenceLink` + `EvidenceSet` types

```task
id: CE-WP-0003-T01
state_hub_task_id: 120b9b5a-9ca3-4dff-8c26-1b5c2e832dc4
priority: critical
status: done
```

Add under `src/shared/`:

- `src/shared/evidence-link.ts` — `EvidenceLink`, `EvidenceLink.status`
  enum per SharedContracts §2.4, `EvidenceLink.relation` enum per §2.5,
  `EvidenceTarget` generic shape
- `src/shared/evidence-set.ts` — `EvidenceSet` with `activeEvidenceItemId`

No services. Pure shapes.

Add a unit test asserting that the union of all enum values matches the
`SharedContracts.md` lists exactly — if someone adds a value without
updating the doc, the test fails.

---

## T02 — Binding service + in-memory link repo + active-state machine

```task
id: CE-WP-0003-T02
state_hub_task_id: f17e251d-4fd7-4ef3-b35c-e8e0dfb3a455
priority: high
status: done
depends_on: [T01]
```

Under `src/binder/`:

- `repos/in-memory-links.ts` — Map-backed `EvidenceLinkRepository`
- `services/bindings.ts` — `linkEvidenceToTarget`, `unlinkEvidence`,
  `listEvidenceForTarget`, `setActiveEvidence`
- `state/active.ts` — a small machine tracking
  `(activeTarget, activeEvidenceItem, activeAnnotation)`. Exposed as a React
  context.

Emit the events from SharedContracts §4 (`EvidenceLinkCreated`,
`EvidenceItemActivated`, `FormFieldActivated`).

---

## T03 — Rect registry (the SharedContracts §7 contract)

```task
id: CE-WP-0003-T03
state_hub_task_id: d3b853ef-7afe-491f-b40b-b6e980a23478
priority: critical
status: done
depends_on: [T02]
```

Implement under `src/binder/visual-guide/`:

- `rect-registry.ts` — `RectRegistry` with `register`, `getRect`,
  `subscribe` per SharedContracts §7
- `react-hooks.ts` — `useRegisterRect(kind, id, ref)` for components to
  register a ref-derived rect
- `events.ts` — registry emits `rect-changed` events on
  scroll/resize/focus/active-evidence-change (use ResizeObserver +
  IntersectionObserver + window resize + window scroll listeners)

Unit tests: register a fake field, evidence card, and highlight; mutate
their bounding rects; assert subscribers fire with the new rects.

**This contract must not change after T03.** Three subsystems will depend on
it in T05/T06/T07.

---

## T04 — Form schema + simple field renderer

```task
id: CE-WP-0003-T04
state_hub_task_id: f42e1ecc-351c-4248-8872-1a25e79d3640
priority: medium
status: done
depends_on: [T01]
```

A deliberately minimal form schema lives in `src/app/forms/demo-schema.ts`:

```ts
type FormFieldSchema =
  | { type: "text"; id: string; label: string }
  | { type: "textarea"; id: string; label: string }
  | { type: "date"; id: string; label: string };
```

JSON Schema is **not** used yet — defer that to a later ADR. The MVP form
just needs to render 3-4 fields and accept evidence links.

- `src/binder/FormRenderer.tsx` renders the schema as a basic form
  (relocated from `src/work/` per `wiki/DependencyMap.md` §2/§5 — `work`
  cannot import `binder`, but FormRenderer needs `useRegisterRect` from
  `binder/visual-guide`. The "evidence-backed form" composition belongs
  in `binder/`; `app/` mounts both `work` panes and `binder` panes
  side-by-side.)
- Each field registers itself with the rect registry as kind `"field"` with
  the field's `id`

---

## T05 — Side-by-side layout + link evidence to field

```task
id: CE-WP-0003-T05
state_hub_task_id: 100fb1ca-6168-4e5d-9dc5-f051e6f9ff61
priority: high
status: done
depends_on: [T02, T04]
```

A new app route `/forms/demo` shows the side-by-side layout from Architecture
§12.2:

- Left: `FormRenderer` with a demo schema (3 fields)
- Right: viewer (reusing `ViewerShell` from CE-WP-0002)
- Bottom strip or popover: evidence list

Linking interaction: click an evidence item, then click a field → link
created. (Drag-and-drop is a polish item, not MVP.) Visual indication on
linked fields (e.g. a chip showing the count of linked evidence items).

---

## T06 — Active-evidence cycling on a field

```task
id: CE-WP-0003-T06
state_hub_task_id: e3bdf1d3-c7a1-484c-8895-8d103e7f9fe6
priority: high
status: done
depends_on: [T05]
```

When a field is focused:

1. Binder loads the field's evidence set.
2. The first evidence item becomes active.
3. The viewer scrolls to and highlights its annotation.
4. Keyboard `Tab`/`Shift-Tab` within the field's evidence chips cycles
   active evidence; viewer scrolls accordingly.
5. The evidence sidebar highlights the active evidence card.

Each evidence card registers itself with the rect registry as
`"evidence-card"`.

---

## T07 — SVG visual guide overlay

```task
id: CE-WP-0003-T07
state_hub_task_id: e2ec50be-d9c5-47dd-b801-9c1afb01e6fd
priority: high
status: done
depends_on: [T03, T06]
```

Implement `src/binder/visual-guide/Overlay.tsx`:

- Single absolutely-positioned SVG covering the viewport
- Subscribes to the rect registry
- On every change, redraws two curves: `field → evidence-card` and
  `evidence-card → highlight`
- Active-only — only the currently active triple gets drawn
- Throttled to animation frames

Acceptance: scroll the viewer, resize the window, change active evidence —
the guide tracks every change without visible lag.

The viewer adapter from CE-WP-0002 must expose
`getHighlightClientRects(annotationId)` so the highlight's rect can be
registered.

---

## T08 — E2E test of PRD scenario steps 5-9

```task
id: CE-WP-0003-T08
state_hub_task_id: e6754c8e-f9e2-435a-af28-31a693c6d9a8
priority: high
status: done
depends_on: [T05, T07]
```

Extend the Playwright E2E from CE-WP-0002-T09:

5. Navigate to `/forms/demo`.
6. Link the previously-created evidence item to the "summary" field.
7. Click the "summary" field.
8. Assert the field, the evidence card, and the highlight all have an
   `aria-current="true"` (or equivalent active marker).
9. Assert the SVG overlay contains exactly two `<path>` elements (one
   field→card, one card→highlight).
10. Scroll the viewer; assert the SVG paths' endpoints update within the
    next animation frame.

If this passes, the form-binding slice is complete and CE-WP-0004 may run
in parallel with any deferred polish work.