feat(08-01): extend SignatureFieldData with type discriminant and helper exports

- Add SignatureFieldType union type with 6 literals (client-signature, initials, text, checkbox, date, agent-signature)
- Add optional type field to SignatureFieldData interface (backward-compat; v1.0 docs have no type)
- Export getFieldType() helper that coalesces field.type ?? 'client-signature'
- Export isClientVisibleField() predicate that returns false for agent-signature only

teressa-copeland-homes/src/lib/db/schema.ts

@@ -1,6 +1,14 @@
 import { jsonb, pgEnum, pgTable, text, timestamp } from "drizzle-orm/pg-core";
 import { relations } from "drizzle-orm";
 
+export type SignatureFieldType =
+  | 'client-signature'
+  | 'initials'
+  | 'text'
+  | 'checkbox'
+  | 'date'
+  | 'agent-signature';
+
 export interface SignatureFieldData {
   id: string;
   page: number;   // 1-indexed
@@ -8,6 +16,25 @@ export interface SignatureFieldData {
   y: number;      // PDF user space, bottom-left origin, points
   width: number;  // PDF points (default: 144 — 2 inches)
   height: number; // PDF points (default: 36 — 0.5 inches)
+  type?: SignatureFieldType;  // Optional — v1.0 documents have no type; fallback = 'client-signature'
+}
+
+/**
+ * Safe field type reader — always returns a SignatureFieldType, never undefined.
+ * v1.0 documents have no `type` on their JSONB fields; this coalesces to 'client-signature'.
+ * ALWAYS use this instead of reading field.type directly.
+ */
+export function getFieldType(field: SignatureFieldData): SignatureFieldType {
+  return field.type ?? 'client-signature';
+}
+
+/**
+ * Returns true for field types that should be visible in the client signing session.
+ * agent-signature fields are embedded during document preparation and must never
+ * surface to the client as required unsigned fields.
+ */
+export function isClientVisibleField(field: SignatureFieldData): boolean {
+  return getFieldType(field) !== 'agent-signature';
 }
 
 export const users = pgTable("users", {