fix: truncate long activity fields before sending to Discord

Apply truncateText to Name, Details, State, and LargeText fields.
Apply truncateURL to DetailsURL, StateURL, LargeURL, and SmallURL fields.
This prevents Discord from silently rejecting the entire presence update.
Fixes #16

rpc.go

@@ -224,6 +224,18 @@ func (r *discordRPC) processImage(imageURL, clientID, token string, ttl int64) (
 func (r *discordRPC) sendActivity(clientID, username, token string, data activity) error {
 	pdk.Log(pdk.LogInfo, fmt.Sprintf("Sending activity for user %s: %s - %s", username, data.Details, data.State))
 
+	// Truncate text fields to Discord's 128-character limit
+	data.Name = truncateText(data.Name)
+	data.Details = truncateText(data.Details)
+	data.State = truncateText(data.State)
+	data.Assets.LargeText = truncateText(data.Assets.LargeText)
+
+	// Omit URLs that exceed Discord's 256-character limit
+	data.DetailsURL = truncateURL(data.DetailsURL)
+	data.StateURL = truncateURL(data.StateURL)
+	data.Assets.LargeURL = truncateURL(data.Assets.LargeURL)
+	data.Assets.SmallURL = truncateURL(data.Assets.SmallURL)
+
 	// Try track artwork first, fall back to Navidrome logo
 	usingDefaultImage := false
 	processedImage, err := r.processImage(data.Assets.LargeImage, clientID, token, imageCacheTTL)

rpc_test.go

@@ -435,6 +435,49 @@ var _ = Describe("discordRPC", func() {
 			})
 			Expect(err).ToNot(HaveOccurred())
 		})
+
+		It("truncates long text fields and omits long URLs", func() {
+			host.CacheMock.On("GetString", discordImageKey).Return("mp:cached/art", true, nil).Once()
+			host.CacheMock.On("GetString", discordImageKey).Return("mp:cached/logo", true, nil).Once()
+
+			longName := strings.Repeat("N", 200)
+			longTitle := strings.Repeat("T", 200)
+			longArtist := strings.Repeat("A", 200)
+			longAlbum := strings.Repeat("B", 200)
+			longURL := "https://example.com/" + strings.Repeat("x", 237)
+
+			host.WebSocketMock.On("SendText", "testuser", mock.MatchedBy(func(msg string) bool {
+				// Text fields should be truncated to 128 runes (127 + "…")
+				truncatedName := strings.Repeat("N", 127) + "…"
+				truncatedTitle := strings.Repeat("T", 127) + "…"
+				truncatedArtist := strings.Repeat("A", 127) + "…"
+				truncatedAlbum := strings.Repeat("B", 127) + "…"
+				return strings.Contains(msg, truncatedName) &&
+					strings.Contains(msg, truncatedTitle) &&
+					strings.Contains(msg, truncatedArtist) &&
+					strings.Contains(msg, truncatedAlbum) &&
+					!strings.Contains(msg, longURL) // URL should be omitted
+			})).Return(nil)
+
+			err := r.sendActivity("client123", "testuser", "token123", activity{
+				Application: "client123",
+				Name:        longName,
+				Type:        2,
+				Details:     longTitle,
+				DetailsURL:  longURL,
+				State:       longArtist,
+				StateURL:    longURL,
+				Assets: activityAssets{
+					LargeImage: "https://example.com/art.jpg",
+					LargeText:  longAlbum,
+					LargeURL:   longURL,
+					SmallImage: navidromeLogoURL,
+					SmallText:  "Navidrome",
+					SmallURL:   longURL,
+				},
+			})
+			Expect(err).ToNot(HaveOccurred())
+		})
 	})
 
 	Describe("clearActivity", func() {