user provisioning: the platform pushes the account list to plugins that declare it

a plugin that creates accounts in an upstream service — jellyfin first, immich
next — needs to know who the platform's users are. it now gets told.

DECLARED IN THE MANIFEST, not asserted at registration. `name` and `handles`
arrive on an unauthenticated socket and are believed, so a capability claimed
there would be a plugin granting itself one. the manifest was reviewed when the
owner installed it, and sits beside `permissions` where "this plugin will be
told who your users are" belongs — on the install screen, not discovered later.

PUSHED, not requested. a sidecar has no authenticated way to ask, so a request
could only be answered, never authorised. a push inverts that: the platform
decides who gets it, and a caller registering under a name with no such
manifest gets nothing.

`listProvisionableUsers` is a hand-written projection — id, email, username,
name, role — and NOT `select *`. `users` holds `password` and `os_user`, and
`getUsers()` returns both, so a plugin reaching for the obvious function would
get every account's password hash. naming the columns means adding a secret to
the table cannot silently add it to what plugins receive. pinned by a test that
asserts the key set, not just the absence of today's secrets.

the owner is excluded. they bypass every permission check and already have
whatever upstream account they want; provisioning them is at best a no-op and
at worst a second admin nobody asked for.

sent after the ack rather than inside it, so registration never waits on a
database query — a slow postgres would otherwise stall every sidecar's startup,
and none of them need the list to start.

and re-sent on every account create and delete, because the registration copy
is a snapshot: a plugin still holding a deleted user would keep an upstream
login alive for someone the platform has removed. read once per broadcast, so
two plugins cannot be told different things about the same moment.

src/servers/plugins/user-provisioning.ts

@@ -0,0 +1,81 @@
+import type { ServerWebSocket } from 'bun';
+import { randomUUID } from 'node:crypto';
+import { listProvisionableUsers } from 'officerdb';
+import { discoverPlugins } from './discover';
+import { socketForSidecar } from '../sidecar-registry';
+
+// Telling a plugin who the platform's users are, so it can create matching accounts upstream.
+//
+// ── Push, not request ──
+//
+// A sidecar has no authenticated way to ask. `/api/sidecar/register` upgrades with `userId: 0` and no
+// token, so anything reaching the port can register — which means a REQUEST for this list could not be
+// authorised, only answered. A push inverts that: the platform decides who gets it, from the manifest the
+// owner reviewed at install, and a caller that registers under a name with no such manifest gets nothing.
+//
+// The list is deliberately modest — id, email, username, name, role, owner excluded. See
+// `listProvisionableUsers`, which is a hand-written projection rather than `select *` so that adding a
+// column to `users` cannot silently add it to what plugins receive.
+//
+// ── Sent again when it changes ──
+//
+// The registration copy is a snapshot, and an account created an hour later would not be in it. So the
+// same message is re-sent on change; a sidecar therefore treats `users:list` as the current truth and
+// replaces what it held, rather than merging.
+
+/** Does this plugin's manifest declare user provisioning? Read from disk, never from the socket. */
+async function declaresUserProvisioning(appName: string): Promise<boolean> {
+  try {
+    const { plugins } = await discoverPlugins();
+    return plugins.some((p) => p.appName === appName && p.manifest.userProvisioning === true);
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Send the account list to one sidecar, if its plugin is entitled to it.
+ *
+ * Never throws: this runs detached from the registration handler, and a failure here must not take down
+ * a socket that is otherwise fine. A plugin that does not receive the list simply has nothing to
+ * provision, which is the same state it is in before the platform has any users.
+ */
+export async function sendProvisionableUsers(ws: ServerWebSocket<unknown>, appName: string): Promise<void> {
+  try {
+    if (!(await declaresUserProvisioning(appName))) return;
+    const users = await listProvisionableUsers();
+    ws.send(JSON.stringify({ type: 'users:list', id: randomUUID(), users }));
+  } catch (error) {
+    console.error(
+      `[user-provisioning] could not send the user list to ${appName}:`,
+      error instanceof Error ? error.message : error,
+    );
+  }
+}
+
+/**
+ * Re-send the list to every plugin entitled to it.
+ *
+ * Called wherever an account appears or disappears. Fire-and-forget on purpose: creating a user must not
+ * fail because a plugin's sidecar is down, and the next registration re-sends anyway.
+ */
+export async function broadcastProvisionableUsers(): Promise<void> {
+  try {
+    const { plugins } = await discoverPlugins();
+    const entitled = plugins.filter((p) => p.manifest.userProvisioning === true);
+    if (!entitled.length) return;
+
+    // Read ONCE for all of them: two plugins must not be told different things about the same moment.
+    const users = await listProvisionableUsers();
+    const payload = JSON.stringify({ type: 'users:list', id: randomUUID(), users });
+
+    for (const plugin of entitled) {
+      const ws = socketForSidecar(plugin.appName);
+      // Not an error. A sidecar that is down gets the list when it next registers, which is the same
+      // path a fresh install takes.
+      if (ws) ws.send(payload);
+    }
+  } catch (error) {
+    console.error('[user-provisioning] broadcast failed:', error instanceof Error ? error.message : error);
+  }
+}