diff --git a/extensions/discord/src/send.outbound.ts b/extensions/discord/src/send.outbound.ts
index 08fcac3a630..6d17d5d7212 100644
--- a/extensions/discord/src/send.outbound.ts
+++ b/extensions/discord/src/send.outbound.ts
@@ -365,15 +365,15 @@ export async function sendWebhookMessageDiscord(
     throw new Error("Discord webhook id/token are required");
   }
 
-  const rewrittenText = rewriteDiscordKnownMentions(text, {
-    accountId: opts.accountId,
-  });
   const replyTo = typeof opts.replyTo === "string" ? opts.replyTo.trim() : "";
   const messageReference = replyTo ? { message_id: replyTo, fail_if_not_exists: false } : undefined;
   const { account, proxyFetch } = resolveDiscordClientAccountContext({
     cfg: opts.cfg,
     accountId: opts.accountId,
   });
+  const rewrittenText = rewriteDiscordKnownMentions(text, {
+    accountId: account.accountId,
+  });
 
   const response = await (proxyFetch ?? fetch)(
     resolveWebhookExecutionUrl({
@@ -430,11 +430,16 @@ export async function sendStickerDiscord(
   stickerIds: string[],
   opts: DiscordSendOpts & { content?: string } = {},
 ): Promise<DiscordSendResult> {
+  const cfg = opts.cfg ?? loadConfig();
+  const accountInfo = resolveDiscordAccount({
+    cfg,
+    accountId: opts.accountId,
+  });
   const { rest, request, channelId } = await resolveDiscordSendTarget(to, opts);
   const content = opts.content?.trim();
   const rewrittenContent = content
     ? rewriteDiscordKnownMentions(content, {
-        accountId: opts.accountId,
+        accountId: accountInfo.accountId,
       })
     : undefined;
   const stickers = normalizeStickerIds(stickerIds);
@@ -456,11 +461,16 @@ export async function sendPollDiscord(
   poll: PollInput,
   opts: DiscordSendOpts & { content?: string } = {},
 ): Promise<DiscordSendResult> {
+  const cfg = opts.cfg ?? loadConfig();
+  const accountInfo = resolveDiscordAccount({
+    cfg,
+    accountId: opts.accountId,
+  });
   const { rest, request, channelId } = await resolveDiscordSendTarget(to, opts);
   const content = opts.content?.trim();
   const rewrittenContent = content
     ? rewriteDiscordKnownMentions(content, {
-        accountId: opts.accountId,
+        accountId: accountInfo.accountId,
       })
     : undefined;
   if (poll.durationSeconds !== undefined) {
diff --git a/extensions/discord/src/send.sends-basic-channel-messages.test.ts b/extensions/discord/src/send.sends-basic-channel-messages.test.ts
index 74e0a17cc7f..a60b98d023a 100644
--- a/extensions/discord/src/send.sends-basic-channel-messages.test.ts
+++ b/extensions/discord/src/send.sends-basic-channel-messages.test.ts
@@ -126,6 +126,40 @@ describe("sendMessageDiscord", () => {
     );
   });
 
+  it("uses configured defaultAccount for cached mention rewriting when accountId is omitted", async () => {
+    rememberDiscordDirectoryUser({
+      accountId: "work",
+      userId: "222333444555666777",
+      handles: ["Alice"],
+    });
+    const { rest, postMock, getMock } = makeDiscordRest();
+    getMock.mockResolvedValueOnce({ type: ChannelType.GuildText });
+    postMock.mockResolvedValue({
+      id: "msg1",
+      channel_id: "789",
+    });
+    await sendMessageDiscord("channel:789", "ping @Alice", {
+      rest,
+      token: "t",
+      cfg: {
+        channels: {
+          discord: {
+            defaultAccount: "work",
+            accounts: {
+              work: {
+                token: "Bot work-token", // pragma: allowlist secret
+              },
+            },
+          },
+        },
+      } as never,
+    });
+    expect(postMock).toHaveBeenCalledWith(
+      Routes.channelMessages("789"),
+      expect.objectContaining({ body: { content: "ping <@222333444555666777>" } }),
+    );
+  });
+
   it("auto-creates a forum thread when target is a Forum channel", async () => {
     const { rest, postMock, getMock } = makeDiscordRest();
     // Channel type lookup returns a Forum channel.