diff --git a/extensions/discord/src/monitor/inbound-worker.ts b/extensions/discord/src/monitor/inbound-worker.ts
index fb34e7e87d8..03be2c234ea 100644
--- a/extensions/discord/src/monitor/inbound-worker.ts
+++ b/extensions/discord/src/monitor/inbound-worker.ts
@@ -11,12 +11,13 @@ import {
 } from "./inbound-dedupe.js";
 import { materializeDiscordInboundJob, type DiscordInboundJob } from "./inbound-job.js";
 import type { RuntimeEnv } from "./message-handler.preflight.types.js";
-import { processDiscordMessage } from "./message-handler.process.js";
-import { deliverDiscordReply } from "./reply-delivery.js";
 import type { DiscordMonitorStatusSink } from "./status.js";
 import { resolveDiscordReplyDeliveryPlan } from "./threading.js";
 import { normalizeDiscordInboundWorkerTimeoutMs, runDiscordTaskWithTimeout } from "./timeouts.js";
 
+type ProcessDiscordMessage = typeof import("./message-handler.process.js").processDiscordMessage;
+type DeliverDiscordReply = typeof import("./reply-delivery.js").deliverDiscordReply;
+
 type DiscordInboundWorkerParams = {
   runtime: RuntimeEnv;
   setStatus?: DiscordMonitorStatusSink;
@@ -32,10 +33,25 @@ export type DiscordInboundWorker = {
 };
 
 export type DiscordInboundWorkerTestingHooks = {
-  processDiscordMessage?: typeof processDiscordMessage;
-  deliverDiscordReply?: typeof deliverDiscordReply;
+  processDiscordMessage?: ProcessDiscordMessage;
+  deliverDiscordReply?: DeliverDiscordReply;
 };
 
+let messageProcessRuntimePromise:
+  | Promise<typeof import("./message-handler.process.js")>
+  | undefined;
+let replyDeliveryRuntimePromise: Promise<typeof import("./reply-delivery.js")> | undefined;
+
+async function loadMessageProcessRuntime() {
+  messageProcessRuntimePromise ??= import("./message-handler.process.js");
+  return await messageProcessRuntimePromise;
+}
+
+async function loadReplyDeliveryRuntime() {
+  replyDeliveryRuntimePromise ??= import("./reply-delivery.js");
+  return await replyDeliveryRuntimePromise;
+}
+
 function formatDiscordRunContextSuffix(job: DiscordInboundJob): string {
   const channelId = job.payload.messageChannelId?.trim();
   const messageId = job.payload.data?.message?.id?.trim();
@@ -62,7 +78,9 @@ async function processDiscordInboundJob(params: {
   let finalReplyStarted = false;
   let createdThreadId: string | undefined;
   let sessionKey: string | undefined;
-  const processDiscordMessageImpl = params.testing?.processDiscordMessage ?? processDiscordMessage;
+  const processDiscordMessageImpl =
+    params.testing?.processDiscordMessage ??
+    (await loadMessageProcessRuntime()).processDiscordMessage;
   try {
     await runDiscordTaskWithTimeout({
       run: async (abortSignal) => {
@@ -135,7 +153,7 @@ async function sendDiscordInboundWorkerTimeoutReply(params: {
   contextSuffix: string;
   createdThreadId?: string;
   sessionKey?: string;
-  deliverDiscordReplyImpl?: typeof deliverDiscordReply;
+  deliverDiscordReplyImpl?: DeliverDiscordReply;
 }) {
   const messageChannelId = params.job.payload.messageChannelId?.trim();
   const messageId = params.job.payload.message?.id?.trim();
@@ -158,7 +176,9 @@ async function sendDiscordInboundWorkerTimeoutReply(params: {
   });
 
   try {
-    await (params.deliverDiscordReplyImpl ?? deliverDiscordReply)({
+    const deliverDiscordReplyImpl =
+      params.deliverDiscordReplyImpl ?? (await loadReplyDeliveryRuntime()).deliverDiscordReply;
+    await deliverDiscordReplyImpl({
       cfg: params.job.payload.cfg,
       replies: [{ text: "Discord inbound worker timed out.", isError: true }],
       target: deliveryPlan.deliverTarget,
diff --git a/extensions/discord/src/monitor/message-handler.ts b/extensions/discord/src/monitor/message-handler.ts
index 56c6dbc7d1e..b63cf304a01 100644
--- a/extensions/discord/src/monitor/message-handler.ts
+++ b/extensions/discord/src/monitor/message-handler.ts
@@ -20,7 +20,6 @@ import {
 } from "./inbound-worker.js";
 import type { DiscordMessageEvent, DiscordMessageHandler } from "./listeners.js";
 import { applyImplicitReplyBatchGate } from "./message-handler.batch-gate.js";
-import { preflightDiscordMessage } from "./message-handler.preflight.js";
 import type { DiscordMessagePreflightParams } from "./message-handler.preflight.types.js";
 import {
   hasDiscordMessageStickers,
@@ -29,6 +28,9 @@ import {
 } from "./message-utils.js";
 import type { DiscordMonitorStatusSink } from "./status.js";
 
+type PreflightDiscordMessage =
+  typeof import("./message-handler.preflight.js").preflightDiscordMessage;
+
 type DiscordMessageHandlerParams = Omit<
   DiscordMessagePreflightParams,
   "ackReactionScope" | "groupPolicy" | "data" | "client"
@@ -40,9 +42,18 @@ type DiscordMessageHandlerParams = Omit<
 };
 
 type DiscordMessageHandlerTestingHooks = DiscordInboundWorkerTestingHooks & {
-  preflightDiscordMessage?: typeof preflightDiscordMessage;
+  preflightDiscordMessage?: PreflightDiscordMessage;
 };
 
+let messagePreflightRuntimePromise:
+  | Promise<typeof import("./message-handler.preflight.js")>
+  | undefined;
+
+async function loadMessagePreflightRuntime() {
+  messagePreflightRuntimePromise ??= import("./message-handler.preflight.js");
+  return await messagePreflightRuntimePromise;
+}
+
 export type DiscordMessageHandlerWithLifecycle = DiscordMessageHandler & {
   deactivate: () => void;
 };
@@ -63,8 +74,7 @@ export function createDiscordMessageHandler(
     params.discordConfig?.ackReactionScope ??
     params.cfg.messages?.ackReactionScope ??
     "group-mentions";
-  const preflightDiscordMessageImpl =
-    params.__testing?.preflightDiscordMessage ?? preflightDiscordMessage;
+  const preflightDiscordMessageImpl = params.__testing?.preflightDiscordMessage;
   const replayGuard = createDiscordInboundReplayGuard();
   const inboundWorker = createDiscordInboundWorker({
     runtime: params.runtime,
@@ -130,7 +140,10 @@ export function createDiscordMessageHandler(
       }
       try {
         if (entries.length === 1) {
-          const ctx = await preflightDiscordMessageImpl({
+          const preflight =
+            preflightDiscordMessageImpl ??
+            (await loadMessagePreflightRuntime()).preflightDiscordMessage;
+          const ctx = await preflight({
             ...params,
             ackReactionScope,
             groupPolicy,
@@ -167,7 +180,10 @@ export function createDiscordMessageHandler(
           ...last.data,
           message: syntheticMessage,
         };
-        const ctx = await preflightDiscordMessageImpl({
+        const preflight =
+          preflightDiscordMessageImpl ??
+          (await loadMessagePreflightRuntime()).preflightDiscordMessage;
+        const ctx = await preflight({
           ...params,
           ackReactionScope,
           groupPolicy,