soulseek, extracted from the platform as a plugin

Seventh plugin out, and the first that was already dead. Soulseek had been
switched off since 2026-08-13: hono.ts had the router import and its mount
commented out, so createSidecarProxy never ran, registerProxiedPrefix was never
called, the slskd:server announcement fired into a void, and officer-slskd was
not in the ecosystem at all. The permission entry had been reduced to api: [],
which is why assertPermissionTotality was satisfied and the server booted
clean. The UI rendered perfectly and every request 404'd.

So this is a resurrection as well as a move.

The mount is now /api/soulseek, derived via mountPrefix from the appName — all
47 frontend call sites repointed from /slskd/. The credential key in
service_connections stays 'slskd': it names the daemon, not the route. Those
two strings differ on purpose and conflating them reads the wrong row.

The connection stays in core service_connections, as transmission does, so
'slskd' remains in a platform union this plugin cannot extend. Recorded in
PLUGIN.md. Unlike transmission this plugin does own a schema: favourites and
the two halves of the cached browse tree, which slskd has no concept of. Those
three tables had been dropped from the drizzle barrel, so bun db:push would
have deleted them on any server holding data.

313 palette classes converted to the semantic tone set, including a shared
PHASE_TONE the three transfer views previously each copied.

sidecar/download.ts

@@ -0,0 +1,56 @@
+import { getSoulseekBrowseDownload } from '../db';
+import { authHeaders, getSlskdConfig } from './upstream';
+
+// Enqueueing downloads out of a cached share tree.
+//
+// slskd's own enqueue endpoint takes a flat list of {filename, size}, which is fine for search results —
+// they arrive as individual files with full paths. A browsed folder is neither: it's a path, and what the
+// user means by clicking it is "everything under here". Expanding that into a file list needs the cache,
+// so it happens HERE rather than in the browser, which would otherwise have to walk the tree one level
+// request at a time and reconstruct paths it only half knows.
+
+/**
+ * A folder can be enormous — the root of one measured peer is 284,166 files. Enqueueing that would be a
+ * misclick that takes the slskd instance down with it, so it's refused with the count rather than
+ * truncated to a silent partial download.
+ */
+export const MAX_ENQUEUE = 10_000;
+
+export class DownloadError extends Error {
+  constructor(
+    message: string,
+    readonly status: number,
+  ) {
+    super(message);
+  }
+}
+
+type EnqueueParams = { userId: number; username: string; path: string; file?: string };
+
+/** Queue one file, or every file beneath one folder, from the cached tree. Returns how many were sent. */
+export async function enqueueFromCache({ userId, username, path, file }: EnqueueParams): Promise<number> {
+  const cfg = await getSlskdConfig(userId);
+  if (!cfg) throw new DownloadError('slskd upstream not configured', 503);
+
+  const files = await getSoulseekBrowseDownload({ userId, username, path, file });
+  if (!files.length) throw new DownloadError('nothing to download at that path', 404);
+  if (files.length > MAX_ENQUEUE) {
+    throw new DownloadError(
+      `${files.length.toLocaleString()} files is over the ${MAX_ENQUEUE.toLocaleString()} limit`,
+      413,
+    );
+  }
+
+  const res = await fetch(`${cfg.base}/api/v0/transfers/downloads/${encodeURIComponent(username)}`, {
+    method: 'POST',
+    headers: { 'content-type': 'application/json', ...authHeaders(cfg) },
+    body: JSON.stringify(files),
+  });
+  if (!res.ok) {
+    const detail = (await res.text().catch(() => '')).slice(0, 200);
+    throw new DownloadError(`slskd returned ${res.status}${detail ? `: ${detail}` : ''}`, 502);
+  }
+
+  console.log(`[slskd] queued ${files.length} file(s) from ${username}: ${file ?? path}`);
+  return files.length;
+}