citation-evidence/wiki/SharedContracts.md

# Shared Contracts — citation-evidence

This document is the **single source of truth** for everything that more than one
subsystem in the citation-evidence ecosystem must agree on:

- the **vocabulary** (entity names and what they mean),
- the **canonical state enums** for entities that flow across repo boundaries,
- the **relation type** vocabulary,
- the **selector type** taxonomy,
- the **event type** vocabulary,
- the **ownership rules** for shared types versus shared behavior.

The five sister repos (`citation-engine`, `evidence-anchor`, `evidence-source`,
`citation-work`, `evidence-binder`) defer to this document. When their
`INTENT.md` files refer to "shared contracts", they mean this file.

During the umbrella-first MVP phase, the **TypeScript implementations** of
these contracts live in `citation-evidence/src/shared/` and are imported by
the per-subsystem code under `citation-evidence/src/{engine,anchor,source,work,binder}/`.
When a subsystem extracts to its own repo, it takes its slice of the shared
types with it — but this document remains the canonical vocabulary.

---

## 1. Vocabulary

These nine entities are the vocabulary every subsystem uses.

| Entity                    | One-line definition                                                                                | Owner (post-extraction) |
|---------------------------|----------------------------------------------------------------------------------------------------|-------------------------|
| `Document`                | An identified source object: PDF, Markdown, HTML, scan, etc.                                       | `citation-engine`       |
| `DocumentRepresentation`  | A normalized, addressable view of a document (canonical text, page map, structure).                | `citation-engine`       |
| `Selector`                | A technical locator for a passage inside a representation.                                         | `citation-engine` (types) / `evidence-anchor` (behavior) |
| `Annotation`              | A technical mark on a document range, expressed as one or more selectors plus quote text.          | `citation-engine`       |
| `EvidenceItem`            | A meaningful evidence object built from one or more annotations, with commentary and status.       | `citation-engine`       |
| `EvidenceSet`             | An ordered group of evidence items associated with a target or topic.                              | `citation-engine` (type) / `evidence-binder` (behavior) |
| `EvidenceLink`            | A relation between an `EvidenceItem` and a structured target (form field, claim, requirement, …). | `citation-engine` (type) / `evidence-binder` (behavior) |
| `CitationCard`            | A renderable, exportable presentation of an evidence item.                                         | `citation-engine`       |
| `CitationRecoveryAttempt` | A traceable attempt to locate a cited passage from an external clue.                               | `citation-engine` (type) / `evidence-source` (behavior) |

**Ownership rule:** *types and interfaces flow downward from `citation-engine`;
behavior flows upward into the specialised repos*. Where the table shows a
split, the engine repo holds the data shape and the other repo holds the
algorithms and lifecycle.

---

## 2. Canonical state enums

These enums are the authoritative values. Subsystems must not invent local
variants without updating this document first.

### 2.1 `Annotation.resolutionStatus`

```
resolved          — selectors located the passage with high confidence
ambiguous         — multiple plausible candidates found
unresolved        — no plausible candidate found
stale             — representation has changed since selectors were stored
```

### 2.2 `EvidenceItem.status`

```
candidate         — captured but not yet vetted
confirmed         — verified by a user as useful evidence
rejected          — explicitly discarded
needs-check       — flagged for review
```

> **Note:** earlier subsystem drafts introduced `strong-support`, `weak-support`,
> and `contradicts` on the item. Those concepts now live on the **link**, not
> the item — see §2.4.

### 2.3 `Document.reviewStatus` (when used by `citation-work`)

```
unreviewed
in-review
relevant
rejected
needs-follow-up
cited
verified
```

`citation-work` may treat any of these as the active state; the canonical
storage lives on the Document record in `citation-engine`.

### 2.4 `EvidenceLink.status` (per target)

```
no-evidence
candidate
confirmed
conflicting
insufficient
verified
```

`no-evidence` is a *derived* state computed when a target has zero links;
it is not stored on a link itself.

### 2.5 `EvidenceLink.relation`

```
supports
contradicts
explains
qualifies
source-for
context-for
```

This is the closed vocabulary for the MVP. Adding a relation requires updating
this document and the `EvidenceLink` schema together.

### 2.6 `CitationRecoveryAttempt.state`

```
created
source-found-fulltext
source-found-preview-only
source-found-metadata-only
source-not-found
quote-found
quote-not-found
candidate-passages-found
manual-confirmation-needed
confirmed
annotation-created
failed
```

---

## 3. Selector taxonomy

A `Selector` is a discriminated union of:

```
TextQuoteSelector         exact quote + prefix/suffix context
TextPositionSelector      canonical text start/end offsets
PdfRectSelector           page number + normalized page rectangles
PdfPageTextSelector       page number + page-local text offsets
DomRangeSelector          DOM path + range offsets (HTML/Markdown)
StructuralSelector        heading/section/AST path
FragmentSelector          exported fragment / deep link (export-only)
```

**Selector redundancy rule:** when an annotation is created, the system stores
*all selector types that are available* for that document representation, not
just one. Resolution tries them in order of expected confidence and stops at
the first high-confidence match.

W3C Web Annotation mapping uses these same concepts but as JSON-LD; the mapping
is documented separately (see ADR-0003 — pending).

---

## 4. Event vocabulary

Events are the primary integration mechanism between subsystems. The closed
event vocabulary for the MVP is:

```
DocumentImported
DocumentRepresentationGenerated
DocumentRemoved
AnnotationCreated
AnnotationResolved
AnnotationResolutionFailed
EvidenceItemCreated
EvidenceItemUpdated
EvidenceLinkCreated
EvidenceLinkUpdated
EvidenceItemActivated
FormFieldActivated
CitationCardRendered
CitationRecoveryStarted
CitationRecoveryCandidateFound
CitationRecoveryConfirmed
SessionCreated
SessionRenamed
SessionDeleted
SessionActivated
```

The `Session*` events live on the cross-session session bus (the
SessionService's own EventBus instance — see CE-WP-0005). The remaining
events live on the per-session engine bus and are scoped to whatever
session is currently active.

Subsystems must emit these events through a shared event bus owned by
`citation-engine`. Subsystems may listen to any event but must not invent
event types without updating this document.

---

## 5. Viewer adapter contract

Viewer adapters are the bridge between a document format and the rest of the
system. They are **owned by `evidence-anchor`** as far as the contract goes;
concrete adapters may live in either `evidence-anchor` or `evidence-source`
depending on whether the heavy lifting is selector logic or document
representation logic.

```ts
interface DocumentViewerAdapter {
  mediaTypes: string[];
  load(document: Document, representation?: DocumentRepresentation): Promise<void>;
  getCurrentSelection(): Promise<SelectionCapture | null>;
  createSelectorsFromSelection(selection: SelectionCapture): Promise<Selector[]>;
  resolveSelectors(selectors: Selector[]): Promise<AnchorResolution>;
  scrollToResolvedTarget(target: ResolvedAnchorTarget, opts?: { center?: boolean; behavior?: "auto"|"smooth" }): Promise<void>;
  renderHighlight(target: ResolvedAnchorTarget, opts?: HighlightRenderOptions): Promise<void>;
  getHighlightClientRects(annotationId: string): Promise<DOMRect[]>;
}
```

MVP delivers a single `PDFViewerAdapter`. HTML and Markdown adapters are
deferred.

---

## 6. Canonical text normalization

All text-based selectors and quote matching depend on a deterministic
normalization function. The MVP normalization is:

1. Unicode NFC normalization.
2. Replace all line-ending sequences with `\n`.
3. Collapse runs of horizontal whitespace into a single space.
4. Strip soft hyphens (U+00AD).
5. Preserve paragraph boundaries (double `\n`).

**This function is versioned.** Stored selectors record the normalization
version they were created against. Changing the function later requires either
backwards-compatible behavior or a re-anchoring migration.

The reference implementation lives in `citation-evidence/src/shared/text/normalize.ts`.

---

## 7. Visual guide rect registry

The visual-guide overlay (form field → evidence card → source highlight)
requires DOM rects from three independently-rendered subsystems. The contract
is a **rect registry** owned by `evidence-binder`:

```ts
interface RectRegistry {
  register(kind: "field" | "evidence-card" | "highlight", id: string, getRect: () => DOMRect | null): () => void;
  getRect(kind: "field" | "evidence-card" | "highlight", id: string): DOMRect | null;
  subscribe(listener: (event: RectRegistryEvent) => void): () => void;
}
```

Each renderer (form, evidence sidebar, viewer adapter) registers a
`getRect` callback. The overlay queries on-demand and re-renders on scroll,
resize, focus, and active-evidence change.

This contract MUST be defined and stable before any of the three renderers
hardens, or the overlay becomes the system's coupling bottleneck.

---

## 8. Ownership rules (the short version)

1. **Types and interfaces** flow downward from `citation-engine`.
2. **Behavior and algorithms** live in the specialised repos.
3. Where a concept appears in both a type and a behavior context (e.g.
   `Selector`, `EvidenceLink`, `EvidenceSet`, `CitationRecoveryAttempt`),
   the engine owns the shape and the specialised repo owns the lifecycle.
4. **The shared event bus is engine-owned**; subsystems publish and subscribe
   but do not extend the event vocabulary unilaterally.
5. **No new enum values, relation types, event types, or selector kinds**
   land in code without first appearing in this document.
6. During umbrella-first MVP: rules 1-5 are aspirational. We will tolerate
   small violations in `citation-evidence/src/` and reconcile during extraction.

---

## 9. Change process

Changes to this document are change to the contract.

- Small additions (a new enum value, a new event type) can be made in a single
  PR that updates this doc + the type definitions + at least one consumer.
- Breaking changes (renaming an entity, removing a state, changing an
  ownership split) require a short ADR in `docs/decisions/` and a heads-up
  progress event on the state-hub.

---

## 10. Pending ADRs that will affect this document

These are listed in `docs/decisions/` once written. Until then the document
reflects the current best understanding from the architecture overview.

- **ADR-0001** — Umbrella-first MVP strategy (decided 2026-05-24, this session).
- **ADR-0002** — Monorepo vs polyrepo packaging (pending).
- **ADR-0003** — W3C Web Annotation: lossy mapping vs round-trip guarantee (pending).
- **ADR-0004** — PDF viewer library choice: `react-pdf-highlighter-plus` vs PDF.js direct (pending).
- **ADR-0005** — Persistence: local-first SQLite vs Postgres from day one (pending).
- **ADR-0006** — Selector ownership split (types in engine, algorithms in anchor) (pending — implied here).