Survive revoice's ffmpeg teardown and explain failed deletions

Switching tracks killed the process: revoice's #cleanUp() dereferences
this.fProc unconditionally, and its own ffmpeg error handler calls stop()
a second time after stop() has already nulled that field. Killing ffmpeg
is what triggers that error, so its handlers are detached first, the
instance's stop() is wrapped defensively (revoice calls it internally),
and an uncaughtException handler keeps the bot in the channel if the
dependency throws from another async callback.

Failed command-message deletions were logged at debug, i.e. invisible in
the default configuration; they now warn with Stoat's error type, and the
README says which permission the bot's role needs.

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

src/core/player.ts

@@ -185,6 +185,18 @@ export class GuildPlayer extends EventEmitter<GuildPlayerEvents> {
     connection.on("userJoin", () => this.clearIdleTimer());
 
     const media = new MediaPlayer(true);
+    // revoice's #cleanUp() dereferences this.fProc unconditionally, so a second
+    // stop() (which its own ffmpeg error handler triggers) throws and would take
+    // the whole process down. Everything it calls goes through this instance
+    // method, so guarding it here covers its internal paths too.
+    const stop = media.stop.bind(media);
+    media.stop = (init?: boolean) => {
+      try {
+        stop(init);
+      } catch (err) {
+        this.log.debug({ err }, "revoice cleanup threw, ignoring");
+      }
+    };
     media.on("startplay", () => {
       this.setStatus(media.paused ? "paused" : "playing");
       this.startTicker();
@@ -298,7 +310,14 @@ export class GuildPlayer extends EventEmitter<GuildPlayerEvents> {
     if (this.media) {
       this.expectingStop = true;
       try {
-        this.media.fProc?.kill("SIGKILL");
+        // Detach revoice's own handlers first: killing ffmpeg makes it emit
+        // "error", and its handler would call stop() again on a half-reset player.
+        const proc = this.media.fProc;
+        if (proc) {
+          proc.removeAllListeners("error");
+          proc.removeAllListeners("end");
+          proc.kill("SIGKILL");
+        }
       } catch {
         // ffmpeg may already be gone.
       }

src/core/revoice.ts

@@ -12,7 +12,7 @@ export interface MediaPlayerLike {
   codecData?: { duration?: string } | null;
   paused: boolean;
   playing: boolean;
-  fProc?: { kill(signal?: string): void } | null;
+  fProc?: { kill(signal?: string): void; removeAllListeners(event?: string): void } | null;
   originStream?: { destroy(): void } | null;
   playStream(input: Readable | string, inputOptions?: string[]): Promise<void>;
   pause(): void;