Discord: several radio streams per voice channel; adding never overwrites (#213)

Owner-reported on live: adding a radio channel for a server + voice channel
that already had one (different label, system, even bot) overwrote the
existing stream and made its bot leave, because stream_id was guild:channel.

- New streams get guild:channel:<12 hex> ids (leases.new_stream_id); old
  guild:channel docs keep working for read/stop/remove/node reports. Route
  validators accept both (leases.STREAM_ID_PATTERN).
- start_stream: no stream_id = ADD. Same system already on in that channel
  is idempotent (already_on, label/mode untouched); a stopped one of that
  system is restarted; anything else is a new doc. stream_id = explicit
  restart/edit (admin Start button, reconciler), incl. moving to another bot.
- preferred_token_id is strict: bot already in this server -> 409
  preferred_busy naming the stream; on another node -> preferred_other_node;
  unusable -> preferred_unavailable. No silent swap. pool_exhausted now says
  one-bot-per-server and to add + invite another bot.
- One-token-per-guild was already enforced inside the lease transaction;
  now covered by race tests. Per-guild asyncio lock serialises the
  already-on / server-cap check with the create (guild half of #223).
- Stop by stream_id (POST /discord/guilds/{id}/stop {stream_id}); admin UI
  Stop/Start/Remove act on the row's stream; node picker lists every stream
  in a channel and adds beside other systems.
- Bot: /leave stream: (autocomplete) stops one; /leave channel: with several
  streams asks which unless all:True; bare /leave still stops the server.
  /status and /join name each stream's bot.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

drb-frontend/lib/c2api.ts

@@ -76,6 +76,9 @@ export const c2api = {
       method: "PUT",
       body: JSON.stringify(body),
     }),
+  /** Without stream_id: ADD a stream to the voice channel (a channel can carry
+   *  several, each its own bot + system; never replaces one). With stream_id:
+   *  restart / edit that stream. */
   startDiscordStream: (body: {
     guild_id: string;
     channel_id: string;
@@ -83,6 +86,7 @@ export const c2api = {
     mode: "persistent" | "adhoc";
     channel_name?: string;
     preferred_token_id?: string;
+    stream_id?: string;
   }) => request<DiscordStream>("/discord/streams", { method: "POST", body: JSON.stringify(body) }),
   /** Permanently remove a radio channel (stopped through desired state first). Admin only. */
   deleteDiscordStream: (streamId: string) =>
@@ -99,10 +103,11 @@ export const c2api = {
     }>(`/discord/guilds/${encodeURIComponent(guildId)}?leave_radio_bots=${leaveRadioBots ? "true" : "false"}`, {
       method: "DELETE",
     }),
-  stopDiscordStream: (guildId: string, channelId: string) =>
+  /** Stop ONE stream (its voice channel may carry others, which keep playing). */
+  stopDiscordStream: (guildId: string, streamId: string) =>
     request<{ stopped: string[] }>(`/discord/guilds/${encodeURIComponent(guildId)}/stop`, {
       method: "POST",
-      body: JSON.stringify({ channel_id: channelId, reason: "stopped from web admin" }),
+      body: JSON.stringify({ stream_id: streamId, reason: "stopped from web admin" }),
     }),
 
   // Node approval

drb-frontend/lib/discord.ts

@@ -67,6 +67,8 @@ export interface DiscordStream {
   stop_reason?: string | null;
   updated_at?: string | null;
   created_at?: string | null;
+  /** POST /discord/streams: this system was already on in that channel — nothing was replaced. */
+  already_on?: boolean;
 }
 
 export interface DiscordGuild {

drb-frontend/lib/discordPicker.ts

@@ -18,7 +18,10 @@ export interface DiscordStreamView {
   channel_id: string;
   guild_name: string | null;
   channel_name: string | null;
+  system_id?: string | null;
   system_name: string | null;
+  /** The radio bot carrying it — tells apart several streams in one voice channel. */
+  token_name?: string | null;
   mode: "persistent" | "adhoc" | null;
   node_id: string | null;
   node_name: string | null;
@@ -35,7 +38,10 @@ export interface DiscordVoiceChannel {
   channel_id: string;
   name: string;
   category: string | null;
+  /** This node's system's stream in the channel, if any — what a pick restarts or moves. */
   stream: DiscordStreamView | null;
+  /** Every live stream in the channel (several systems can share it, each its own bot). */
+  streams?: DiscordStreamView[];
 }
 
 export interface DiscordGuildOption {