refactor(P060): keep loadDocument on the bridge (not exposed as LLM tool)

Restores `bridge.loadDocument` + `LoadDocumentInput`. The method stays
available for direct host-app consumers / SDK adapters; it is NOT in
LLM_STATIC_TOOLS or ClientToolName, so the LLM cannot invoke it via the
copilot tool registry. This separates the bridge surface (full iframe
contract) from the LLM-tool surface (a curated subset).

Author: bendersej

copilot/src/lib/embed-bridge/bridge.ts

@@ -6,6 +6,7 @@ import {
   FocusFieldInput,
   GetDocumentContentInput,
   GoToInput,
+  LoadDocumentInput,
   MovePageInput,
   RotatePageInput,
   SelectToolInput,
@@ -51,6 +52,7 @@ const getRequestTimeoutMs = (requestType: BridgeRequestType): number => {
     case 'GET_FIELDS':
     case 'DOWNLOAD':
     case 'GO_TO':
+    case 'LOAD_DOCUMENT':
     case 'MOVE_PAGE':
     case 'ROTATE_PAGE':
     case 'SELECT_TOOL':
@@ -403,6 +405,7 @@ export const createBridge = ({
   }
   const bridge: IframeBridge = {
     getState: () => state,
+    loadDocument: (args) => parseAndSend(LoadDocumentInput, 'LOAD_DOCUMENT', args),
     getFields: () => sendRequest<{ fields: FieldRecord[] }>('GET_FIELDS', {}),
     getDocumentContent: (args) => parseAndSend<typeof GetDocumentContentInput, DocumentContentResult>(
       GetDocumentContentInput,

copilot/src/lib/embed-bridge/index.ts

@@ -11,6 +11,7 @@ export {
   GetDocumentContentInput,
   GetFieldsInput,
   GoToInput,
+  LoadDocumentInput,
   MovePageInput,
   NoInput,
   RotatePageInput,

copilot/src/lib/embed-bridge/schemas.ts

@@ -98,3 +98,14 @@ export const SubmitInput = z
 export const DownloadInput = NoInput.describe(
   'Finalizes the filled PDF and triggers an in-browser download for the user. Use only when the user asks to download.',
 )
+
+// Bridge-only — not exposed as an LLM tool. Direct callers (host apps,
+// SDK adapters) load documents via this; the copilot demo itself bootstraps
+// from URL params and doesn't currently use it.
+export const LoadDocumentInput = z
+  .object({
+    data_url: z.string(),
+    name: z.string().optional(),
+    page: z.number().int().positive().optional(),
+  })
+  .describe('Loads a PDF document into the editor by URL or data-URL.')

copilot/src/lib/embed-bridge/types.ts

@@ -74,6 +74,7 @@ export type BridgeState =
 // Request type union. Every postMessage the bridge sends carries one of these
 // as its `type` field. The editor honours each.
 export type BridgeRequestType =
+  | 'LOAD_DOCUMENT'
   | 'GO_TO'
   | 'SELECT_TOOL'
   | 'DETECT_FIELDS'
@@ -98,6 +99,7 @@ export type FocusFieldResult = { hint: { type: 'user_action_expected'; message:
 // re-validate.
 export type IframeBridge = {
   getState: () => BridgeState
+  loadDocument: (args: unknown) => Promise<BridgeResult>
   getFields: () => Promise<BridgeResult<{ fields: FieldRecord[] }>>
   getDocumentContent: (args: unknown) => Promise<BridgeResult<DocumentContentResult>>
   detectFields: () => Promise<BridgeResult<{ detected_count: number }>>