Add Relay cursor pagination guide

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

contrib/claude/relay.md

@@ -0,0 +1,101 @@
+# Relay Cursor Pagination
+
+This project implements [Relay-style cursor pagination](https://relay.dev/graphql/connections.htm) for all list fields across GraphQL APIs.
+
+## Schema types
+
+Every paginated field uses the same set of types:
+
+```graphql
+type PageInfo {
+    hasNextPage: Boolean!
+    hasPreviousPage: Boolean!
+    startCursor: CursorKey
+    endCursor: CursorKey
+}
+
+enum OrderDirection {
+    ASC
+    DESC
+}
+```
+
+Each entity defines its own order field enum, order input, connection, and edge:
+
+```graphql
+enum VendorOrderField {
+    CREATED_AT
+    NAME
+}
+
+input VendorOrder {
+    direction: OrderDirection!
+    field: VendorOrderField!
+}
+
+type VendorConnection {
+    totalCount: Int!
+    edges: [VendorEdge!]!
+    pageInfo: PageInfo!
+}
+
+type VendorEdge {
+    cursor: CursorKey!
+    node: Vendor!
+}
+```
+
+## Field arguments
+
+Connection fields on parent types always use the standard Relay arguments:
+
+```graphql
+type Organization {
+    vendors(
+        first: Int
+        after: CursorKey
+        last: Int
+        before: CursorKey
+        orderBy: VendorOrder
+        filter: VendorFilter
+    ): VendorConnection!
+}
+```
+
+- `first` / `after` — forward pagination (returns `Head` position)
+- `last` / `before` — backward pagination (returns `Tail` position)
+- `orderBy` — optional, defaults to `CREATED_AT` / `DESC`
+- `filter` — optional, entity-specific filtering
+
+## Cursor format
+
+Cursors are opaque `CursorKey` scalars. Internally they encode as base64url(JSON):
+
+```
+["<entity_global_id>", <sort_field_value>]
+```
+
+For example, a cursor sorting by `created_at` encodes the entity ID and its `created_at` timestamp. This enables keyset pagination — the database uses the cursor values to seek directly to the right position instead of using OFFSET.
+
+## Keyset pagination
+
+The database query uses the cursor to build a WHERE clause that skips to the correct position:
+
+- For `DESC` ordering: rows where `(field <= cursor_value) AND NOT (field = cursor_value AND id > cursor_id)`
+- For `ASC` ordering: rows where `(field >= cursor_value) AND NOT (field = cursor_value AND id < cursor_id)`
+
+The query fetches `size + 1` (or `size + 2` when a cursor is provided) rows to detect whether more pages exist in either direction. `NewPage` trims the extra rows and sets `hasNextPage` / `hasPreviousPage` accordingly.
+
+For backward pagination (`last` / `before`), the SQL sort direction is reversed, and the result slice is reversed back to the correct order before building edges.
+
+## Default page size
+
+When neither `first` nor `last` is provided, the default page size is **25**.
+
+## Adding a new paginated field — checklist
+
+1. **Schema** — add `enum XxxOrderField`, `input XxxOrder`, `type XxxConnection`, `type XxxEdge`, and the connection field with Relay arguments on the parent type
+2. **Coredata** — add `*_order_field.go` (with `Column()`, `IsValid()`, marshaling), `CursorKey(field)` method on the entity, and the `LoadAllBy*` query using cursor SQL fragments + `page.NewPage()`
+3. **API types** — add `*_connection.go` with `OrderBy` alias, connection struct, `NewXxxConnection`, `NewXxxEdge`
+4. **Resolver** — implement the resolver (authorize, build order, build cursor, call service, build connection)
+5. **Codegen** — run `go generate` for the relevant API package