offscale, extracted from the platform into its own repository

The tailnet plugin — machines, users, pre-auth keys, access policy and device
invites. Moved out of officerdev/platform, where it had lived in plugins/ since
the plugin system was built.

Until now this code existed in exactly one place: the platform repository. That
made "gitignore the plugins directory" impossible to do safely, because
untracking it would have left 49 files on a single disk with no remote. This
repository is what makes that move safe.

Same extraction as plugins/music before it: source only, no history. The
platform's history still holds every commit that shaped this, and the SHAs cited
across the codebase keep resolving — replaying it here would have created a
second, divergent account of the same work.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/useHeadscaleServers.ts

@@ -0,0 +1,102 @@
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
+import { useClient } from 'hooks/useClient';
+import type { HeadscaleServer, HeadscaleHealth, HeadscaleSshTest } from './shared';
+
+// The registered-servers cache. Every panel in the /headscale workspace reads this one query, so switching
+// the active server anywhere updates the whole screen at once.
+//
+// Registration is validated server-side before anything is saved (reachable, >=0.29, key accepted), which
+// means a POST can fail for perfectly ordinary reasons — a typo'd URL, a revoked key. Those are not
+// exceptional here, so the mutations surface their message rather than swallowing it.
+
+const SERVERS_KEY = ['headscale', 'servers'] as const;
+const EMPTY: HeadscaleServer[] = [];
+
+const BASE = '/offscale/_officer/servers';
+
+/**
+ * Readable message from a useClient rejection. It throws `{status, message}` where `message` is the raw
+ * body text — JSON `{error}` from our sidecar, but plain text from the platform's own 401/503 paths.
+ */
+export function headscaleErrorMessage(err: unknown): string {
+  const raw = (err as { message?: unknown } | null)?.message;
+  if (typeof raw !== 'string' || !raw) return 'Something went wrong';
+  try {
+    const parsed = JSON.parse(raw) as { error?: unknown };
+    if (typeof parsed.error === 'string' && parsed.error) return parsed.error;
+  } catch {
+    /* plain text */
+  }
+  return raw.slice(0, 300);
+}
+
+export type RegisterServerInput = { name?: string; url: string; apiKey: string; sshHost?: string };
+/** `sshHost: ''` clears the console target; omitting it leaves whatever is stored alone. */
+export type UpdateServerInput = { id: number; name?: string; url?: string; apiKey?: string; sshHost?: string };
+
+export function useHeadscaleServers() {
+  const { get, post, patch, delete: del } = useClient();
+  const qc = useQueryClient();
+
+  const query = useQuery({
+    queryKey: SERVERS_KEY,
+    queryFn: () => get<{ servers: HeadscaleServer[] }>(BASE),
+    staleTime: 30_000,
+  });
+
+  const invalidate = () => qc.invalidateQueries({ queryKey: SERVERS_KEY });
+
+  const register = useMutation({
+    mutationFn: (input: RegisterServerInput) => post<{ server: HeadscaleServer }>(BASE, input),
+    onSuccess: invalidate,
+  });
+
+  const update = useMutation({
+    mutationFn: ({ id, ...rest }: UpdateServerInput) => patch<{ server: HeadscaleServer }>(`${BASE}/${id}`, rest),
+    onSuccess: invalidate,
+  });
+
+  const remove = useMutation({
+    mutationFn: (id: number) => del(`${BASE}/${id}`),
+    onSuccess: invalidate,
+  });
+
+  const activate = useMutation({
+    mutationFn: (id: number) => post<{ server: HeadscaleServer }>(`${BASE}/${id}/activate`),
+    // Deleting or switching reshuffles which server is active, and every domain query is scoped to it.
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['headscale'] }),
+  });
+
+  const servers = query.data?.servers ?? EMPTY;
+
+  return {
+    servers,
+    active: servers.find((s) => s.isActive) ?? null,
+    isLoading: query.isLoading,
+    error: query.error,
+    refetch: query.refetch,
+    register,
+    update,
+    remove,
+    activate,
+  };
+}
+
+/**
+ * Try to open a shell on a console target with the keys already on this machine. Takes the host rather than a
+ * server id so the form can test a value before it is saved — which is when a typo is still cheap to fix.
+ */
+export function useHeadscaleSshTest() {
+  const { post } = useClient();
+  return useMutation({
+    mutationFn: (host: string) => post<HeadscaleSshTest>('/offscale/_officer/ssh-test', { host }),
+  });
+}
+
+/** On-demand reachability probe for one server. Never automatic — it costs two upstream round trips. */
+export function useHeadscaleHealth() {
+  const { get } = useClient();
+  return useMutation({
+    mutationFn: (id: number) => get<HeadscaleHealth>(`${BASE}/${id}/health`),
+  });
+}