diff --git a/api/fofos-client.ts b/api/fofos-client.ts
index 71fb9f2..4d30a72 100644
--- a/api/fofos-client.ts
+++ b/api/fofos-client.ts
@@ -48,6 +48,14 @@ type RequestOptions = {
   /** Already-serialised. Forwarded as given so what fofos receives is what the caller sent. */
   body?: string | FormData | null;
   contentType?: string | null;
+  /**
+   * Who is asking, as an email — sent as `X-Actor`, and written into fofos's own change history.
+   *
+   * fofos has no users, so it cannot work this out and cannot check it: the header is as trustworthy
+   * as the token that carried it. That is enough for what it is for, which is telling two colleagues
+   * apart rather than proving anything.
+   */
+  actor?: string | null;
 };
 
 export type FofosResponse = { status: number; body: string; contentType: string | null };
@@ -70,6 +78,7 @@ export async function fofosRequest(
   // Left unset for FormData: fetch has to write its own, including the multipart boundary, and a
   // hand-set Content-Type here produces a body the other end cannot parse.
   if (options.contentType) headers['Content-Type'] = options.contentType;
+  if (options.actor) headers['X-Actor'] = options.actor;
 
   let response: Response;
   try {
diff --git a/api/router.ts b/api/router.ts
index f911546..dabe833 100644
--- a/api/router.ts
+++ b/api/router.ts
@@ -762,6 +762,9 @@ router.all('/*', async (ctx) => {
       search: url.search,
       body,
       contentType: body ? 'application/json' : null,
+      // Officer's session is the only place the acting user is known. fofos writes it into its own
+      // history — see its record.ts, and the note on `actor` in fofos-client.
+      actor: ctx.get('user')?.email ?? null,
     });
     return passThrough(response);
   } catch (error) {