refactor: prune legacy group prefixes

src/discord/monitor/message-handler.process.ts

@@ -223,7 +223,7 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
 
   const effectiveFrom = isDirectMessage
     ? `discord:${author.id}`
-    : (autoThreadContext?.From ?? `group:${message.channelId}`);
+    : (autoThreadContext?.From ?? `discord:channel:${message.channelId}`);
   const effectiveTo = autoThreadContext?.To ?? replyTarget;
   if (!effectiveTo) {
     runtime.error?.(danger("discord: missing reply target"));

src/discord/monitor/native-command.ts

@@ -601,7 +601,11 @@ async function dispatchDiscordCommandInteraction(params: {
     RawBody: prompt,
     CommandBody: prompt,
     CommandArgs: commandArgs,
-    From: isDirectMessage ? `discord:${user.id}` : `group:${channelId}`,
+    From: isDirectMessage
+      ? `discord:${user.id}`
+      : isGroupDm
+        ? `discord:group:${channelId}`
+        : `discord:channel:${channelId}`,
     To: `slash:${user.id}`,
     SessionKey: `agent:${route.agentId}:${sessionPrefix}:${user.id}`,
     CommandTargetSessionKey: route.sessionKey,

src/discord/monitor/threading.test.ts

@@ -28,7 +28,7 @@ describe("resolveDiscordAutoThreadContext", () => {
     });
     expect(context).not.toBeNull();
     expect(context?.To).toBe("channel:thread");
-    expect(context?.From).toBe("group:thread");
+    expect(context?.From).toBe("discord:channel:thread");
     expect(context?.OriginatingTo).toBe("channel:thread");
     expect(context?.SessionKey).toBe(
       buildAgentSessionKey({

src/discord/monitor/threading.ts

@@ -194,7 +194,7 @@ export function resolveDiscordAutoThreadContext(params: {
 
   return {
     createdThreadId,
-    From: `group:${createdThreadId}`,
+    From: `${params.channel}:channel:${createdThreadId}`,
     To: `channel:${createdThreadId}`,
     OriginatingTo: `channel:${createdThreadId}`,
     SessionKey: threadSessionKey,