refactor(server): delete webhook once on startup, no retry

The Bot API GET reliably clears the webhook, so the retry loop added for the
empty-body POST is no longer needed. One best-effort call; log on failure.

cmd/server/main.go

@@ -146,7 +146,12 @@ func main() {
 	// Clear any webhook left over from the AWS deployment at startup, before the
 	// owner DM and before polling. getUpdates (long polling, below) returns HTTP
 	// 409 while a webhook is set, so a stuck webhook silently breaks the bot.
-	clearWebhook(rootCtx, cfg.TelegramBotToken)
+	// Best-effort, one shot: a real failure here is logged, not retried.
+	if err := telegram.DeleteWebhook(rootCtx, cfg.TelegramBotToken); err != nil {
+		log.Warn("deleteWebhook failed; getUpdates may 409 if a webhook is set", "err", err)
+	} else {
+		log.Info("webhook cleared")
+	}
 
 	deploynotify.Run(rootCtx, deploynotify.Config{
 		Bot:     b,
@@ -193,42 +198,6 @@ func main() {
 	}
 }
 
-// webhookDeleteAttempts bounds the startup webhook-clear retries, and
-// webhookDeleteBackoff is the wait between them. Telegram's edge sometimes
-// returns an empty body on the first request after a cold container start
-// ("unexpected end of JSON input"); a short retry rides over that blip so long
-// polling is not left blocked by a stale webhook.
-const (
-	webhookDeleteAttempts = 5
-	webhookDeleteBackoff  = 1 * time.Second
-)
-
-// clearWebhook deletes any configured webhook so getUpdates (long polling) does
-// not 409. It is best-effort but retried so a flaky network does not leave the
-// bot permanently unable to poll. Uses telegram.DeleteWebhook (a plain Bot API
-// GET) rather than the go-telegram helper, whose empty-multipart POST comes back
-// with an empty body in some environments. Pending updates are kept so the
-// poller drains the buffered queue for a lossless cutover.
-func clearWebhook(ctx context.Context, token string) {
-	for attempt := 1; attempt <= webhookDeleteAttempts; attempt++ {
-		err := telegram.DeleteWebhook(ctx, token)
-		if err == nil {
-			log.Info("webhook cleared", "attempt", attempt)
-			return
-		}
-		log.Warn("deleteWebhook failed", "attempt", attempt, "err", err)
-		if attempt == webhookDeleteAttempts {
-			break
-		}
-		select {
-		case <-ctx.Done():
-			return
-		case <-time.After(webhookDeleteBackoff):
-		}
-	}
-	log.Warn("deleteWebhook still failing after retries; getUpdates may 409 if a webhook is set")
-}
-
 // buildProvider picks the storage backend. Selection order:
 //  1. Explicit KV_PROVIDER env (memory|mongodb) wins.
 //  2. Auto-detect: MONGO_URL set → mongodb; otherwise memory.