diff --git a/desktop/src/features/forum/ui/ForumComposer.lifecycle.test.mjs b/desktop/src/features/forum/ui/ForumComposer.lifecycle.test.mjs
index 91c8b01157..ec6770829c 100644
--- a/desktop/src/features/forum/ui/ForumComposer.lifecycle.test.mjs
+++ b/desktop/src/features/forum/ui/ForumComposer.lifecycle.test.mjs
@@ -141,9 +141,10 @@ async function setup(options = {}) {
     },
     "@/features/channels/hooks": {
       useAddChannelMembersMutation: () => ({
-        mutateAsync: async () => {
-          calls.push(["add"]);
+        mutateAsync: async (input) => {
+          calls.push(["add", input]);
           if (control.add) await control.add.promise;
+          if (control.onAdd) control.onAdd(input);
           return { errors: [] };
         },
       }),
@@ -1215,3 +1216,52 @@ for (const main of [false, true])
     assert.ok(sends[0].flat(2).includes(HUMAN));
     assert.ok(sends[0].flat(2).includes(KEY));
   });
+
+// A forum signs only current members, so a person outside the channel must
+// be invited first, as a member. Cancel keeps the draft and sends nothing.
+for (const choice of ["invite", "cancel"]) {
+  test(`mounted forum asks before mentioning a person outside the channel: ${choice}`, async () => {
+    const s = await setup({ realMentions: true });
+    s.control.cachedMembers = [
+      { pubkey: HUMAN, role: "member", isAgent: false, displayName: "Pat" },
+    ];
+    s.control.liveMembers = [PAT];
+    s.navigate("b");
+    await s.open();
+    await s.choose("Pat");
+    const text = s.text;
+    // Pat leaves the cached roster too, so the composer knows to ask.
+    s.control.cachedMembers = [];
+    s.control.liveMembers = [];
+    s.navigate("a");
+    s.navigate("b");
+    await act(async () => {});
+    s.control.onAdd = ({ pubkeys }) => {
+      s.control.liveMembers = pubkeys.includes(HUMAN) ? [PAT] : [];
+    };
+    await s.submit();
+    assert.equal(s.prompt.open, true);
+    assert.deepEqual([...s.prompt.names], ["Pat"]);
+    if (choice === "invite") await s.invite();
+    else await s.dismiss();
+    await act(async () => {});
+    const sends = s.calls.filter(([name]) => name === "send");
+    if (choice === "cancel") {
+      assert.equal(sends.length, 0);
+      assert.equal(s.text.trim(), text.trim(), "the draft is kept");
+      return;
+    }
+    assert.deepEqual(
+      s.calls
+        .filter(([name]) => name === "add")
+        .map(([, { channelId, pubkeys, role }]) => ({
+          channelId,
+          pubkeys: [...pubkeys],
+          role,
+        })),
+      [{ channelId: "forum", pubkeys: [HUMAN], role: "member" }],
+    );
+    assert.equal(sends.length, 1);
+    assert.ok(sends[0].flat(2).includes(HUMAN), "the invited person is tagged");
+  });
+}
diff --git a/desktop/src/features/forum/ui/useForumMentionPreparation.ts b/desktop/src/features/forum/ui/useForumMentionPreparation.ts
index 3289a5e806..1866f8d828 100644
--- a/desktop/src/features/forum/ui/useForumMentionPreparation.ts
+++ b/desktop/src/features/forum/ui/useForumMentionPreparation.ts
@@ -11,6 +11,7 @@ type PendingInvite = {
   pubkeys: string[];
   nonMemberPubkeys: string[];
   intendedAgentPubkeys: string[];
+  agentPubkeys: ReadonlySet<string>;
   resolve: (invited: boolean) => void;
 };
 
@@ -72,15 +73,16 @@ export function useForumMentionPreparation(
           .map((ref) => ref.pubkey),
       ];
       const agentPubkeys = new Set(intendedAgentPubkeys.map(normalizePubkey));
-      // Local managed-agent lifecycle and channel-less/notes surfaces are not
-      // part of this adapter. Relay-only agents use the same bot add as chat.
+      // Publication signs only current members, so a mentioned nonmember must
+      // be invited first. People join as members and relay-only agents use
+      // the same bot add as chat. Local managed-agent lifecycle and
+      // channel-less/notes surfaces are not part of this adapter.
       const nonMemberPubkeys =
         capturedChannelId &&
         channelType === "forum" &&
         mentions.hasResolvedMembers
           ? [...new Set(pubkeys.map(normalizePubkey))].filter(
               (pubkey) =>
-                agentPubkeys.has(pubkey) &&
                 !mentions.isManagedAgentPubkey(pubkey) &&
                 !mentions.memberPubkeys.has(pubkey),
             )
@@ -92,6 +94,7 @@ export function useForumMentionPreparation(
             pubkeys,
             nonMemberPubkeys,
             intendedAgentPubkeys,
+            agentPubkeys,
             resolve,
           };
           pendingRef.current = draft;
@@ -140,15 +143,21 @@ export function useForumMentionPreparation(
         intendedAgentPubkeys: draft.intendedAgentPubkeys,
       });
       if (!isCurrent()) return;
-      const result = await addMembers.mutateAsync({
-        channelId: draft.channelId,
-        pubkeys: draft.nonMemberPubkeys,
-        role: "bot",
-      });
-      if (!isCurrent()) return;
-      if (result.errors.length > 0) {
-        setError(result.errors.map((failure) => failure.error).join("; "));
-        return;
+      for (const role of ["member", "bot"] as const) {
+        const pubkeys = draft.nonMemberPubkeys.filter(
+          (pubkey) => draft.agentPubkeys.has(pubkey) === (role === "bot"),
+        );
+        if (pubkeys.length === 0) continue;
+        const result = await addMembers.mutateAsync({
+          channelId: draft.channelId,
+          pubkeys,
+          role,
+        });
+        if (!isCurrent()) return;
+        if (result.errors.length > 0) {
+          setError(result.errors.map((failure) => failure.error).join("; "));
+          return;
+        }
       }
       pendingRef.current = null;
       setPending(null);
diff --git a/desktop/tests/e2e/mention-clipboard.spec.ts b/desktop/tests/e2e/mention-clipboard.spec.ts
index 19cd599c08..81083e11c9 100644
--- a/desktop/tests/e2e/mention-clipboard.spec.ts
+++ b/desktop/tests/e2e/mention-clipboard.spec.ts
@@ -796,7 +796,11 @@ test("forum post and reply selection copies carry the mention", async ({
   await expect(input).toHaveText(FORUM_REPLY_BODY);
   await expect(input.locator(".mention-chip")).toHaveText("John Smith");
 
+  // John is not in the forum: a forum signs only members, so it asks first.
   await page.getByTestId("send-message").click();
+  const dialog = page.getByRole("alertdialog");
+  await expect(dialog).toContainText("John Smith");
+  await dialog.getByRole("button", { name: "Invite", exact: true }).click();
   await expect(input).toHaveText("");
   await expect
     .poll(() => readSentMentionPubkeys(page, FORUM_REPLY_BODY))