refactor(discord): centralize autoThread reply plan (#856)

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

@@ -25,9 +25,7 @@ import {
 import { buildDirectLabel, buildGuildLabel, resolveReplyContext } from "./reply-context.js";
 import { deliverDiscordReply } from "./reply-delivery.js";
 import {
-  maybeCreateDiscordAutoThread,
-  resolveDiscordAutoThreadContext,
-  resolveDiscordReplyDeliveryPlan,
+  resolveDiscordAutoThreadReplyPlan,
   resolveDiscordThreadStarter,
 } from "./threading.js";
 import { sendTyping } from "./typing.js";
@@ -201,35 +199,22 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
 	    parentSessionKey,
 	    useSuffix: false,
 	  });
-	  const inboundTarget = `channel:${message.channelId}`;
-	  const createdThreadId = await maybeCreateDiscordAutoThread({
+	  const replyPlan = await resolveDiscordAutoThreadReplyPlan({
 	    client,
 	    message,
 	    isGuildMessage,
 	    channelConfig,
-    threadChannel,
+	    threadChannel,
 	    baseText: baseText ?? "",
 	    combinedBody,
-	  });
-	  const replyPlan = resolveDiscordReplyDeliveryPlan({
-	    replyTarget: inboundTarget,
 	    replyToMode,
-	    messageId: message.id,
-	    threadChannel,
-	    createdThreadId,
+	    agentId: route.agentId,
+	    channel: route.channel,
 	  });
 	  const deliverTarget = replyPlan.deliverTarget;
 	  const replyTarget = replyPlan.replyTarget;
 	  const replyReference = replyPlan.replyReference;
-
-	  const autoThreadContext = isGuildMessage
-	    ? resolveDiscordAutoThreadContext({
-	        agentId: route.agentId,
-	        channel: route.channel,
-	        messageChannelId: message.channelId,
-	        createdThreadId,
-	      })
-	    : null;
+	  const autoThreadContext = replyPlan.autoThreadContext;
 
 	  const effectiveFrom = isDirectMessage
 	    ? `discord:${author.id}`

src/discord/monitor/threading.test.ts

@@ -1,6 +1,11 @@
 import { describe, expect, it } from "vitest";
 import { buildAgentSessionKey } from "../../routing/resolve-route.js";
-import { resolveDiscordAutoThreadContext } from "./threading.js";
+import type { Client } from "@buape/carbon";
+import {
+  resolveDiscordAutoThreadContext,
+  resolveDiscordAutoThreadReplyPlan,
+  resolveDiscordReplyDeliveryPlan,
+} from "./threading.js";
 
 describe("resolveDiscordAutoThreadContext", () => {
   it("returns null when no createdThreadId", () => {
@@ -42,3 +47,88 @@ describe("resolveDiscordAutoThreadContext", () => {
   });
 });
 
+describe("resolveDiscordReplyDeliveryPlan", () => {
+  it("uses reply references when posting to the original target", () => {
+    const plan = resolveDiscordReplyDeliveryPlan({
+      replyTarget: "channel:parent",
+      replyToMode: "all",
+      messageId: "m1",
+      threadChannel: null,
+      createdThreadId: null,
+    });
+    expect(plan.deliverTarget).toBe("channel:parent");
+    expect(plan.replyTarget).toBe("channel:parent");
+    expect(plan.replyReference.use()).toBe("m1");
+  });
+
+  it("disables reply references when autoThread creates a new thread", () => {
+    const plan = resolveDiscordReplyDeliveryPlan({
+      replyTarget: "channel:parent",
+      replyToMode: "all",
+      messageId: "m1",
+      threadChannel: null,
+      createdThreadId: "thread",
+    });
+    expect(plan.deliverTarget).toBe("channel:thread");
+    expect(plan.replyTarget).toBe("channel:thread");
+    expect(plan.replyReference.use()).toBeUndefined();
+  });
+
+  it("always uses existingId when inside a thread", () => {
+    const plan = resolveDiscordReplyDeliveryPlan({
+      replyTarget: "channel:thread",
+      replyToMode: "off",
+      messageId: "m1",
+      threadChannel: { id: "thread" },
+      createdThreadId: null,
+    });
+    expect(plan.replyReference.use()).toBe("m1");
+  });
+});
+
+describe("resolveDiscordAutoThreadReplyPlan", () => {
+  it("switches delivery + session context to the created thread", async () => {
+    const client = {
+      rest: { post: async () => ({ id: "thread" }) },
+    } as unknown as Client;
+    const plan = await resolveDiscordAutoThreadReplyPlan({
+      client,
+      message: { id: "m1", channelId: "parent" } as unknown as import("./listeners.js").DiscordMessageEvent["message"],
+      isGuildMessage: true,
+      channelConfig: { autoThread: true } as unknown as import("./allow-list.js").DiscordChannelConfigResolved,
+      threadChannel: null,
+      baseText: "hello",
+      combinedBody: "hello",
+      replyToMode: "all",
+      agentId: "agent",
+      channel: "discord",
+    });
+    expect(plan.deliverTarget).toBe("channel:thread");
+    expect(plan.replyReference.use()).toBeUndefined();
+    expect(plan.autoThreadContext?.SessionKey).toBe(
+      buildAgentSessionKey({
+        agentId: "agent",
+        channel: "discord",
+        peer: { kind: "channel", id: "thread" },
+      }),
+    );
+  });
+
+  it("does nothing when autoThread is disabled", async () => {
+    const client = { rest: { post: async () => ({ id: "thread" }) } } as unknown as Client;
+    const plan = await resolveDiscordAutoThreadReplyPlan({
+      client,
+      message: { id: "m1", channelId: "parent" } as unknown as import("./listeners.js").DiscordMessageEvent["message"],
+      isGuildMessage: true,
+      channelConfig: { autoThread: false } as unknown as import("./allow-list.js").DiscordChannelConfigResolved,
+      threadChannel: null,
+      baseText: "hello",
+      combinedBody: "hello",
+      replyToMode: "all",
+      agentId: "agent",
+      channel: "discord",
+    });
+    expect(plan.deliverTarget).toBe("channel:parent");
+    expect(plan.autoThreadContext).toBeNull();
+  });
+});

src/discord/monitor/threading.ts

@@ -202,6 +202,51 @@ export function resolveDiscordAutoThreadContext(params: {
   };
 }
 
+export type DiscordAutoThreadReplyPlan = DiscordReplyDeliveryPlan & {
+  createdThreadId?: string;
+  autoThreadContext: DiscordAutoThreadContext | null;
+};
+
+export async function resolveDiscordAutoThreadReplyPlan(params: {
+  client: Client;
+  message: DiscordMessageEvent["message"];
+  isGuildMessage: boolean;
+  channelConfig?: DiscordChannelConfigResolved | null;
+  threadChannel?: DiscordThreadChannel | null;
+  baseText: string;
+  combinedBody: string;
+  replyToMode: ReplyToMode;
+  agentId: string;
+  channel: string;
+}): Promise<DiscordAutoThreadReplyPlan> {
+  const originalReplyTarget = `channel:${params.message.channelId}`;
+  const createdThreadId = await maybeCreateDiscordAutoThread({
+    client: params.client,
+    message: params.message,
+    isGuildMessage: params.isGuildMessage,
+    channelConfig: params.channelConfig,
+    threadChannel: params.threadChannel,
+    baseText: params.baseText,
+    combinedBody: params.combinedBody,
+  });
+  const deliveryPlan = resolveDiscordReplyDeliveryPlan({
+    replyTarget: originalReplyTarget,
+    replyToMode: params.replyToMode,
+    messageId: params.message.id,
+    threadChannel: params.threadChannel,
+    createdThreadId,
+  });
+  const autoThreadContext = params.isGuildMessage
+    ? resolveDiscordAutoThreadContext({
+        agentId: params.agentId,
+        channel: params.channel,
+        messageChannelId: params.message.channelId,
+        createdThreadId,
+      })
+    : null;
+  return { ...deliveryPlan, createdThreadId, autoThreadContext };
+}
+
 export async function maybeCreateDiscordAutoThread(params: {
   client: Client;
   message: DiscordMessageEvent["message"];