fix(API): hide SYSTEM_AUTHOR_ID from listAuthorsOfPad

doc/api/http_api.adoc

@@ -654,6 +654,8 @@ _Example returns:_
 
 returns an array of authors who contributed to this pad
 
+The synthetic `a.etherpad-system` author (used internally when content is inserted without an explicit `authorId` — HTTP API `setText`/`appendText`/`setHTML` calls without `authorId`, server-side imports, plugins like `ep_post_data`) is omitted from the returned list.
+
 _Example returns:_
 
   * `{code: 0, message:"ok", data: {authorIDs : ["a.s8oes9dhwrvt0zif", "a.akf8finncvomlqva"]}`

doc/api/http_api.md

@@ -698,6 +698,8 @@ return true of false
 
 returns an array of authors who contributed to this pad
 
+The synthetic `a.etherpad-system` author (used internally when content is inserted without an explicit `authorId` — HTTP API `setText`/`appendText`/`setHTML` calls without `authorId`, server-side imports, plugins like `ep_post_data`) is omitted from the returned list.
+
 *Example returns:*
 * `{code: 0, message:"ok", data: {authorIDs : ["a.s8oes9dhwrvt0zif", "a.akf8finncvomlqva"]}`
 * `{code: 1, message:"padID does not exist", data: null}`

src/node/db/API.ts

@@ -831,7 +831,13 @@ Example returns:
 exports.listAuthorsOfPad = async (padID: string) => {
   // get the pad
   const pad = await getPadSafe(padID, true);
-  const authorIDs = pad.getAllAuthors();
+  // Pad.SYSTEM_AUTHOR_ID is the synthetic author Etherpad attributes inserts to
+  // when no authorId is supplied (HTTP API setText/appendText/setHTML without
+  // authorId, server-side import flows, plugins like ep_post_data). It is an
+  // implementation detail of changeset bookkeeping, not a real contributor, so
+  // it should not surface through this public API.
+  const {Pad} = require('./Pad');
+  const authorIDs = pad.getAllAuthors().filter((id: string) => id !== Pad.SYSTEM_AUTHOR_ID);
   return {authorIDs};
 };