feat(discord): follow threads after first mention

internal/channels/discord/discord.go

@@ -34,6 +34,11 @@ type Channel struct {
 	audioMgr        *audio.Manager              // unified STT via audio.Manager (nil = no STT)
 	// pairingService, pairingDebounce, approvedGroups, groupHistory, historyLimit, requireMention
 	// are inherited from channels.BaseChannel.
+
+	// mentionedThreads tracks thread/channel IDs where the bot was @mentioned.
+	// Once mentioned in a thread, respond to ALL subsequent messages without requiring another mention.
+	mentionedThreads   map[string]bool
+	mentionedThreadsMu sync.Mutex
 }
 
 // New creates a new Discord channel from config.
@@ -66,12 +71,13 @@ func New(cfg config.DiscordConfig, msgBus *bus.MessageBus, pairingSvc store.Pair
 	}
 
 	ch := &Channel{
-		BaseChannel:     base,
-		session:         session,
-		config:          cfg,
-		agentStore:      agentStore,
-		configPermStore: configPermStore,
-		audioMgr:        audioMgr,
+		BaseChannel:      base,
+		session:          session,
+		config:           cfg,
+		agentStore:       agentStore,
+		configPermStore:  configPermStore,
+		audioMgr:         audioMgr,
+		mentionedThreads: make(map[string]bool),
 	}
 	ch.SetRequireMention(requireMention)
 	ch.SetPairingService(pairingSvc)

internal/channels/discord/handler.go

@@ -187,7 +187,33 @@ func (c *Channel) handleMessage(_ *discordgo.Session, m *discordgo.MessageCreate
 	// When not mentioned, record message to pending history for later context.
 	// `mentioned` was pre-computed above for policy gating.
 	if peerKind == "group" && c.RequireMention() {
-		if !mentioned {
+		// Check if this message is in a thread where bot was previously mentioned.
+		inMentionedThread := false
+		if c.isThreadChannel(ctx, channelID) {
+			c.mentionedThreadsMu.Lock()
+			inMentionedThread = c.mentionedThreads[channelID]
+			c.mentionedThreadsMu.Unlock()
+		}
+
+		if mentioned {
+			// Track this thread so future messages don't need a mention.
+			if c.isThreadChannel(ctx, channelID) {
+				c.mentionedThreadsMu.Lock()
+				c.mentionedThreads[channelID] = true
+				// Cap to prevent unbounded growth
+				if len(c.mentionedThreads) > 5000 {
+					i := 0
+					for k := range c.mentionedThreads {
+						if i >= 2500 {
+							break
+						}
+						delete(c.mentionedThreads, k)
+						i++
+					}
+				}
+				c.mentionedThreadsMu.Unlock()
+			}
+		} else if !inMentionedThread {
 			// Collect media file paths for group history context.
 			var mediaPaths []string
 			for _, mf := range mediaFiles {