the notify sidecar stops trusting whoever reaches it

to send one message to four accounts an hour ago i found the sidecar's
ephemeral port and POSTed to it directly, once per user, with no
authentication of any kind. that worked, which was the problem: the same
door was open to anything else on the machine, including a commander with
a shell.

two changes.

POST /api/notify/broadcast, owner only via `ownerOnly` on the permission —
the supported way to say one thing to everyone. teams will narrow it later;
today the choice is everyone or one person.

and the sidecar now requires a secret on everything under /_officer/. it
is generated per boot, held in memory, announced to the platform over the
registration socket beside the port, and never written to disk.

X-Officer-User could not carry this on its own, and my first attempt got
that wrong: it says WHO is asking, and a caller on loopback can write it
itself. only the secret says the PLATFORM is asking. so the check covers
the whole /_officer/ surface rather than just the send route — /_officer/
devices takes the same header to decide whose phones are listed and
deleted.

what it bounds, honestly: a MEMBER's commander runs as its own Linux user
and cannot read this process, so for every account but the owner's this is
kernel-enforced. the owner's own commander runs as the owner, same as the
platform, and is not bounded by this and cannot be — the same reason
`execution` permissions are never grantable. the owner's decision, and
this is a real improvement rather than a boundary.

`bun run notify:test` posts to that port and will now be refused. it is a
developer CLI on a box where the platform is running; left to fail loudly
rather than given a way in.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Officer-Session: 656f5c85-e49a-4f1f-b9f3-042a04b4d043

src/servers/api/notify/router.ts

@@ -1,4 +1,6 @@
 import { createSidecarProxy } from '../../sidecar/create-proxy';
+import { getUsers } from 'officerdb';
+import * as errors from '../../custom-errors';
 
 // /api/notify/* — auth, then forward to officer-notify. The apps register their push tokens through here
 // and nothing else uses it; producers inside the tailnet POST to the sidecar over loopback directly.
@@ -7,7 +9,68 @@ import { createSidecarProxy } from '../../sidecar/create-proxy';
 
 const proxy = createSidecarProxy({ name: 'notify', prefix: '/api/notify' });
 
+/*
+  POST /api/notify/broadcast — one message to every account, owner only.
+
+  It exists because the alternative was what actually happened on 2026-08-24: to reach four accounts at
+  once, somebody found the sidecar's ephemeral port and POSTed to it directly, once per user, with no
+  authentication at all. That worked, which was the problem — the same door was open to anything else on
+  the machine, including an agent.
+
+  Teams will narrow this later. Today the choice is everyone or one person, and everyone is owner-only.
+*/
+proxy.router.post('/broadcast', async (ctx) => {
+  type BroadcastBody = { title?: string; body?: string; code?: string };
+  const body: BroadcastBody = await ctx.req.json<BroadcastBody>().catch(() => ({}) as BroadcastBody);
+  const title = body.title?.trim();
+  const message = body.body?.trim();
+  if (!title || !message) throw errors.BAD_REQUEST('title and body are required');
+
+  const base = proxy.getHttpUrl();
+  const producer = notifyProducerHeaders();
+  if (!base || !producer) throw errors.createError(503, 'notify sidecar not available');
+
+  // Sequential, and deliberately so: this is a handful of accounts on a personal server, and one slow
+  // APNs call must not turn into a hundred concurrent ones against the same host.
+  const results: { userId: number; ok: boolean }[] = [];
+  for (const user of await getUsers()) {
+    try {
+      const res = await fetch(`${base}/_officer/notify`, {
+        method: 'POST',
+        headers: { 'content-type': 'application/json', ...producer },
+        // `userId` in the BODY, with no `X-Officer-User`: this is the platform speaking about someone
+        // else, which is exactly the distinction `sidecar/notify/resolve-user.ts` draws.
+        body: JSON.stringify({ code: body.code ?? 'officer/core:message', userId: user.id, title, body: message }),
+        signal: AbortSignal.timeout(15_000),
+      });
+      results.push({ userId: user.id, ok: res.ok });
+    } catch {
+      // One account's failure must not stop the rest — a broadcast that gives up halfway is worse than
+      // one that reports which half landed.
+      results.push({ userId: user.id, ok: false });
+    }
+  }
+
+  return ctx.json({ sent: results.filter((r) => r.ok).length, total: results.length, results });
+});
+
 export const notifyRouter = proxy.router;
 
 /** Base URL of the sidecar's HTTP server, or null if it hasn't reported in yet. */
 export const getNotifyServerUrl = proxy.getHttpUrl;
+
+/**
+ * The header an in-process producer must send when it calls the sidecar directly.
+ *
+ * Producers inside the platform — sendoff, chat — bypass this proxy and POST over loopback, because they
+ * are notifying somebody other than the caller and the proxy pins the target to whoever is signed in.
+ * That path used to accept anyone who could reach the port, which on a machine running commanders is
+ * anyone with a shell.
+ *
+ * Null before the sidecar registers, in which case the producer is right to give up rather than send
+ * unauthenticated.
+ */
+export function notifyProducerHeaders(): Record<string, string> | null {
+  const secret = proxy.getProducerSecret();
+  return secret ? { 'X-Officer-Producer': secret } : null;
+}