fix(discord): prevent duplicate link expansion and add regex tests

Address Copilot review feedback:
- Move resolveDiscordRefs(content) before the referenced message
  concatenation to prevent message links in quoted replies from being
  expanded twice.
- Add unit tests for channelRefRe and msgLinkRe regex patterns,
  covering valid/invalid inputs and the 3-link cap.

pkg/channels/discord/discord.go

@@ -345,6 +345,10 @@ func (c *DiscordChannel) handleMessage(s *discordgo.Session, m *discordgo.Messag
 		content = c.stripBotMention(content)
 	}
 
+	// Resolve Discord refs in main content before concatenation to avoid
+	// double-expanding links that appear in the referenced message.
+	content = c.resolveDiscordRefs(s, content, m.GuildID)
+
 	// Prepend referenced (quoted) message content if this is a reply
 	if m.MessageReference != nil && m.ReferencedMessage != nil {
 		refContent := m.ReferencedMessage.Content
@@ -358,7 +362,6 @@ func (c *DiscordChannel) handleMessage(s *discordgo.Session, m *discordgo.Messag
 				refAuthor, refContent, content)
 		}
 	}
-	content = c.resolveDiscordRefs(s, content, m.GuildID)
 
 	senderID := m.Author.ID
 

pkg/channels/discord/discord_resolve_test.go

@@ -0,0 +1,98 @@
+package discord
+
+import (
+	"testing"
+)
+
+func TestChannelRefRegex(t *testing.T) {
+	tests := []struct {
+		name   string
+		input  string
+		wantID string
+		wantOK bool
+	}{
+		{"basic channel ref", "<#123456789>", "123456789", true},
+		{"long id", "<#9876543210123456>", "9876543210123456", true},
+		{"no match plain text", "hello world", "", false},
+		{"no match partial", "<#>", "", false},
+		{"no match letters", "<#abc>", "", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			matches := channelRefRe.FindStringSubmatch(tt.input)
+			if tt.wantOK {
+				if len(matches) < 2 || matches[1] != tt.wantID {
+					t.Errorf("channelRefRe(%q) = %v, want ID %q", tt.input, matches, tt.wantID)
+				}
+			} else {
+				if len(matches) >= 2 {
+					t.Errorf("channelRefRe(%q) should not match, got %v", tt.input, matches)
+				}
+			}
+		})
+	}
+}
+
+func TestMsgLinkRegex(t *testing.T) {
+	tests := []struct {
+		name      string
+		input     string
+		wantGuild string
+		wantChan  string
+		wantMsg   string
+		wantOK    bool
+	}{
+		{
+			"discord.com link",
+			"https://discord.com/channels/111/222/333",
+			"111", "222", "333", true,
+		},
+		{
+			"discordapp.com link",
+			"https://discordapp.com/channels/111/222/333",
+			"111", "222", "333", true,
+		},
+		{
+			"real world ids",
+			"check this https://discord.com/channels/9000000000000001/9000000000000002/9000000000000003 please",
+			"9000000000000001", "9000000000000002", "9000000000000003", true,
+		},
+		{"no match http", "http://discord.com/channels/1/2/3", "", "", "", false},
+		{"no match missing segment", "https://discord.com/channels/1/2", "", "", "", false},
+		{"no match plain text", "hello world", "", "", "", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			matches := msgLinkRe.FindStringSubmatch(tt.input)
+			if tt.wantOK {
+				if len(matches) < 4 {
+					t.Fatalf("msgLinkRe(%q) didn't match, want guild=%s chan=%s msg=%s",
+						tt.input, tt.wantGuild, tt.wantChan, tt.wantMsg)
+				}
+				if matches[1] != tt.wantGuild || matches[2] != tt.wantChan || matches[3] != tt.wantMsg {
+					t.Errorf("msgLinkRe(%q) = guild=%s chan=%s msg=%s, want %s/%s/%s",
+						tt.input, matches[1], matches[2], matches[3],
+						tt.wantGuild, tt.wantChan, tt.wantMsg)
+				}
+			} else {
+				if len(matches) >= 4 {
+					t.Errorf("msgLinkRe(%q) should not match, got %v", tt.input, matches)
+				}
+			}
+		})
+	}
+}
+
+func TestMsgLinkRegex_MultipleMatches(t *testing.T) {
+	input := "see https://discord.com/channels/1/2/3 and https://discord.com/channels/4/5/6 and https://discord.com/channels/7/8/9 and https://discord.com/channels/10/11/12"
+	matches := msgLinkRe.FindAllStringSubmatch(input, 3)
+	if len(matches) != 3 {
+		t.Fatalf("expected 3 matches (capped), got %d", len(matches))
+	}
+	// Verify the 3rd match is 7/8/9 (not 10/11/12)
+	if matches[2][1] != "7" || matches[2][2] != "8" || matches[2][3] != "9" {
+		t.Errorf("3rd match = %v, want guild=7 chan=8 msg=9", matches[2])
+	}
+}