diff --git a/desktop/playwright.config.ts b/desktop/playwright.config.ts
index b6296f0f3..c0ecf0ba3 100644
--- a/desktop/playwright.config.ts
+++ b/desktop/playwright.config.ts
@@ -47,6 +47,7 @@ export default defineConfig({
         "**/edit-agent.spec.ts",
         "**/doctor-cta-screenshots.spec.ts",
         "**/pubkey-display-screenshots.spec.ts",
+        "**/ambiguous-agent-owner-suffix.spec.ts",
         "**/file-attachment.spec.ts",
         "**/image-attachment-gallery.spec.ts",
         "**/composer-image-draw.spec.ts",
diff --git a/desktop/src/features/channels/ui/MembersSidebar.tsx b/desktop/src/features/channels/ui/MembersSidebar.tsx
index 48a04b591..44cf2f777 100644
--- a/desktop/src/features/channels/ui/MembersSidebar.tsx
+++ b/desktop/src/features/channels/ui/MembersSidebar.tsx
@@ -20,7 +20,12 @@ import {
   useUserSearchFetchMoreOnScroll,
   useUsersBatchQuery,
 } from "@/features/profile/hooks";
-import { formatOwnerLabel } from "@/features/profile/lib/identity";
+import {
+  countVisibleDisplayNames,
+  formatDisambiguatedAgentName,
+  formatOwnerLabel,
+  hasVisibleDisplayNameCollision,
+} from "@/features/profile/lib/identity";
 import { rankUserCandidatesBySearch } from "@/features/profile/lib/userCandidateSearch";
 import { usePresenceQuery } from "@/features/presence/hooks";
 import { useIdentityQuery } from "@/shared/api/hooks";
@@ -374,6 +379,13 @@ export function MembersSidebar({
     userSearchResults,
     rawMembers,
   ]);
+  const addSearchNameCounts = React.useMemo(
+    () =>
+      countVisibleDisplayNames(
+        addSearchResults.map((user) => formatAddCandidateName(user)),
+      ),
+    [addSearchResults],
+  );
   const isAddSearchLoading =
     userSearchQuery.isLoading ||
     managedAgentsQuery.isLoading ||
@@ -708,23 +720,39 @@ export function MembersSidebar({
                             Not in this channel
                           </SearchResultSectionTitle>
                         ) : null}
-                        {addSearchResults.map((user) => (
-                          <AddMemberSearchResultRow
-                            disabled={
-                              addingMemberPubkeys.has(user.pubkey) || isArchived
-                            }
-                            key={user.pubkey}
-                            onSelect={(selectedUser) => {
-                              void handleAddSearchResult(selectedUser);
-                            }}
-                            ownerLabel={formatOwnerLabel(
-                              user.ownerPubkey,
-                              identityQuery.data?.pubkey,
-                              addSearchOwnerProfilesQuery.data?.profiles,
-                            )}
-                            user={user}
-                          />
-                        ))}
+                        {addSearchResults.map((user) => {
+                          const ownerLabel = formatOwnerLabel(
+                            user.ownerPubkey,
+                            identityQuery.data?.pubkey,
+                            addSearchOwnerProfilesQuery.data?.profiles,
+                          );
+                          const displayName = formatAddCandidateName(user);
+
+                          return (
+                            <AddMemberSearchResultRow
+                              disabled={
+                                addingMemberPubkeys.has(user.pubkey) ||
+                                isArchived
+                              }
+                              displayName={formatDisambiguatedAgentName({
+                                displayName,
+                                hasNameCollision:
+                                  hasVisibleDisplayNameCollision(
+                                    displayName,
+                                    addSearchNameCounts,
+                                  ),
+                                isAgent: user.isAgent,
+                                ownerLabel,
+                              })}
+                              key={user.pubkey}
+                              onSelect={(selectedUser) => {
+                                void handleAddSearchResult(selectedUser);
+                              }}
+                              ownerLabel={ownerLabel}
+                              user={user}
+                            />
+                          );
+                        })}
                         {isAddSearchLoading ? (
                           <p className="px-4 py-3 text-sm text-muted-foreground">
                             Searching...
@@ -851,11 +879,13 @@ function SearchResultSectionTitle({
 
 function AddMemberSearchResultRow({
   disabled,
+  displayName,
   onSelect,
   ownerLabel,
   user,
 }: {
   disabled: boolean;
+  displayName: string;
   onSelect: (user: UserSearchResult) => void;
   ownerLabel?: string | null;
   user: UserSearchResult;
@@ -869,7 +899,7 @@ function AddMemberSearchResultRow({
       data-testid={`channel-user-search-result-${user.pubkey}`}
     >
       <button
-        aria-label={`Select ${formatAddCandidateName(user)}`}
+        aria-label={`Select ${displayName}`}
         className="absolute inset-0 z-0 cursor-pointer focus-visible:outline-hidden focus-visible:ring-1 focus-visible:ring-ring"
         disabled={disabled}
         onClick={() => onSelect(user)}
@@ -885,8 +915,11 @@ function AddMemberSearchResultRow({
         {user.isAgent ? (
           <div className="min-w-0">
             <div className="flex min-w-0 items-center gap-2">
-              <span className="truncate text-sm font-medium tracking-tight">
-                {formatAddCandidateName(user)}
+              <span
+                className="truncate text-sm font-medium tracking-tight"
+                data-testid="channel-user-search-result-name"
+              >
+                {displayName}
               </span>
               <span className="inline-flex shrink-0 items-center gap-1 text-xs text-muted-foreground">
                 <Bot aria-hidden="true" className="h-4 w-4" />
diff --git a/desktop/src/features/messages/ui/MentionAutocomplete.tsx b/desktop/src/features/messages/ui/MentionAutocomplete.tsx
index 8f54606f4..de1d98646 100644
--- a/desktop/src/features/messages/ui/MentionAutocomplete.tsx
+++ b/desktop/src/features/messages/ui/MentionAutocomplete.tsx
@@ -12,6 +12,11 @@ import {
 import { UserAvatar } from "@/shared/ui/UserAvatar";
 import { safeNpub } from "@/shared/lib/nostrUtils";
 import { truncatePubkey } from "@/shared/lib/pubkey";
+import {
+  countVisibleDisplayNames,
+  formatDisambiguatedAgentName,
+  hasVisibleDisplayNameCollision,
+} from "@/features/profile/lib/identity";
 
 export type MentionSuggestion = {
   pubkey?: string;
@@ -66,12 +71,11 @@ export const MentionAutocomplete = React.memo(function MentionAutocomplete({
 
   // Name collisions are the impersonation vector: a vanity-ground key can
   // wear any display name. When two suggestions share a name, surface each
-  // one's npub (truncated; full key in the hover tooltip) to tell them apart.
-  const nameCounts = new Map<string, number>();
-  for (const suggestion of suggestions) {
-    const name = suggestion.displayName.toLowerCase();
-    nameCounts.set(name, (nameCounts.get(name) ?? 0) + 1);
-  }
+  // one's owner in the title (when known) and npub (truncated; full key in the
+  // hover tooltip) to tell them apart.
+  const nameCounts = countVisibleDisplayNames(
+    suggestions.map((suggestion) => suggestion.displayName),
+  );
 
   return (
     <div
@@ -101,8 +105,16 @@ export const MentionAutocomplete = React.memo(function MentionAutocomplete({
             (suggestion.teamId ? `team-${suggestion.teamId}` : null) ??
             suggestion.displayName;
           const agentLabel = "agent";
-          const hasNameCollision =
-            (nameCounts.get(suggestion.displayName.toLowerCase()) ?? 0) > 1;
+          const hasNameCollision = hasVisibleDisplayNameCollision(
+            suggestion.displayName,
+            nameCounts,
+          );
+          const displayName = formatDisambiguatedAgentName({
+            displayName: suggestion.displayName,
+            hasNameCollision,
+            isAgent: suggestion.isAgent,
+            ownerLabel: suggestion.ownerLabel,
+          });
           const collisionNpub =
             hasNameCollision && suggestion.pubkey
               ? safeNpub(suggestion.pubkey)
@@ -140,9 +152,10 @@ export const MentionAutocomplete = React.memo(function MentionAutocomplete({
               <span className="flex min-w-0 flex-1 flex-col gap-0.5">
                 <span
                   className="min-w-0 break-words font-medium leading-snug"
-                  title={suggestion.displayName}
+                  data-testid="mention-suggestion-name"
+                  title={displayName}
                 >
-                  {suggestion.displayName}
+                  {displayName}
                 </span>
                 {suggestion.kind === "team" ||
                 suggestion.isAgent ||
diff --git a/desktop/src/features/messages/ui/NewMessageResultRow.tsx b/desktop/src/features/messages/ui/NewMessageResultRow.tsx
index 8fab14122..4e3df3749 100644
--- a/desktop/src/features/messages/ui/NewMessageResultRow.tsx
+++ b/desktop/src/features/messages/ui/NewMessageResultRow.tsx
@@ -1,6 +1,9 @@
 import { Bot } from "lucide-react";
 
-import { formatOwnerLabel } from "@/features/profile/lib/identity";
+import {
+  formatDisambiguatedAgentName,
+  formatOwnerLabel,
+} from "@/features/profile/lib/identity";
 import type { UserProfileLookup } from "@/features/profile/lib/identity";
 import { ProfileAvatar } from "@/features/profile/ui/ProfileAvatar";
 import type { UserSearchResult } from "@/shared/api/types";
@@ -67,6 +70,7 @@ function HoverRecipientIdentity({
 export function NewMessageResultRow({
   currentPubkey,
   disabled,
+  hasNameCollision = false,
   isAlreadySelected = false,
   isKeyboardHighlighted = false,
   onSelect,
@@ -75,6 +79,7 @@ export function NewMessageResultRow({
 }: {
   currentPubkey?: string;
   disabled: boolean;
+  hasNameCollision?: boolean;
   isAlreadySelected?: boolean;
   isKeyboardHighlighted?: boolean;
   onSelect: (user: UserSearchResult) => void;
@@ -87,6 +92,12 @@ export function NewMessageResultRow({
     currentPubkey,
     ownerProfiles,
   );
+  const displayName = formatDisambiguatedAgentName({
+    displayName: name,
+    hasNameCollision,
+    isAgent: user.isAgent,
+    ownerLabel,
+  });
 
   return (
     <div
@@ -94,7 +105,7 @@ export function NewMessageResultRow({
       data-keyboard-highlighted={isKeyboardHighlighted ? "true" : undefined}
     >
       <button
-        aria-label={`${isAlreadySelected ? "Already added" : "Add"} ${name}`}
+        aria-label={`${isAlreadySelected ? "Already added" : "Add"} ${displayName}`}
         aria-selected={isAlreadySelected || isKeyboardHighlighted}
         className={cn(
           "group/dm-result flex min-h-14 w-full cursor-pointer items-center gap-3 px-4 py-3.5 text-left transition-colors duration-150 ease-out hover:bg-muted/40 focus-visible:bg-muted/40 focus-visible:outline-hidden focus-visible:ring-1 focus-visible:ring-ring disabled:cursor-not-allowed disabled:opacity-60",
@@ -120,7 +131,7 @@ export function NewMessageResultRow({
               <div className="flex min-w-0 items-center gap-2">
                 <div className="flex min-w-0 flex-1">
                   <HoverRecipientIdentity
-                    displayName={name}
+                    displayName={displayName}
                     pubkey={user.pubkey}
                   />
                 </div>
diff --git a/desktop/src/features/messages/ui/NewMessageScreen.tsx b/desktop/src/features/messages/ui/NewMessageScreen.tsx
index 4e212c523..868836f8e 100644
--- a/desktop/src/features/messages/ui/NewMessageScreen.tsx
+++ b/desktop/src/features/messages/ui/NewMessageScreen.tsx
@@ -7,6 +7,10 @@ import {
 } from "@/features/channels/hooks";
 import type { Channel } from "@/shared/api/types";
 import { useSendMessageMutation } from "@/features/messages/hooks";
+import {
+  countVisibleDisplayNames,
+  hasVisibleDisplayNameCollision,
+} from "@/features/profile/lib/identity";
 import { getKeyboardSearchSelection } from "@/features/profile/lib/userCandidateSearch";
 import { SelectedRecipientChip } from "@/features/profile/ui/SelectedRecipientChip";
 import { useIdentityQuery } from "@/shared/api/hooks";
@@ -72,6 +76,13 @@ export function NewMessageScreen() {
   const isSearchTransitionPending = searchQuery.trim() !== deferredSearchQuery;
   const visibleSearchResults =
     isSearchTransitionPending || isDirectoryLoading ? [] : searchResults;
+  const visibleSearchNameCounts = React.useMemo(
+    () =>
+      countVisibleDisplayNames(
+        visibleSearchResults.map((user) => formatRecipientName(user)),
+      ),
+    [visibleSearchResults],
+  );
   const showRecipientPicker = isRecipientPickerOpen && !isPending;
   const highlightedRecipientIndex = React.useMemo(() => {
     if (!showRecipientPicker || visibleSearchResults.length === 0) {
@@ -518,6 +529,10 @@ export function NewMessageScreen() {
                           isKeyboardHighlighted={
                             highlightedRecipient?.pubkey === user.pubkey
                           }
+                          hasNameCollision={hasVisibleDisplayNameCollision(
+                            formatRecipientName(user),
+                            visibleSearchNameCounts,
+                          )}
                           key={user.pubkey}
                           onSelect={handleResultSelect}
                           ownerProfiles={ownerProfiles}
diff --git a/desktop/src/features/profile/lib/identity.test.mjs b/desktop/src/features/profile/lib/identity.test.mjs
index 282152e03..d5d9c158d 100644
--- a/desktop/src/features/profile/lib/identity.test.mjs
+++ b/desktop/src/features/profile/lib/identity.test.mjs
@@ -1,7 +1,61 @@
 import assert from "node:assert/strict";
 import test from "node:test";
 
-import { profileLookupsEqual } from "./identity.ts";
+import {
+  countVisibleDisplayNames,
+  formatDisambiguatedAgentName,
+  hasVisibleDisplayNameCollision,
+  profileLookupsEqual,
+} from "./identity.ts";
+
+test("formatDisambiguatedAgentName appends an owner for colliding agents", () => {
+  assert.equal(
+    formatDisambiguatedAgentName({
+      displayName: "Bumble",
+      hasNameCollision: true,
+      isAgent: true,
+      ownerLabel: "sergior",
+    }),
+    "Bumble (sergior)",
+  );
+  assert.equal(
+    formatDisambiguatedAgentName({
+      displayName: "Bumble",
+      hasNameCollision: true,
+      isAgent: true,
+      ownerLabel: "you",
+    }),
+    "Bumble (you)",
+  );
+});
+
+test("formatDisambiguatedAgentName leaves humans and unique agents unchanged", () => {
+  assert.equal(
+    formatDisambiguatedAgentName({
+      displayName: "Bumble",
+      hasNameCollision: true,
+      isAgent: false,
+      ownerLabel: null,
+    }),
+    "Bumble",
+  );
+  assert.equal(
+    formatDisambiguatedAgentName({
+      displayName: "Bumble",
+      hasNameCollision: false,
+      isAgent: true,
+      ownerLabel: "sergior",
+    }),
+    "Bumble",
+  );
+});
+
+test("visible display-name collisions are case-insensitive", () => {
+  const counts = countVisibleDisplayNames(["Bumble", " bUmBlE ", "Fizz"]);
+
+  assert.equal(hasVisibleDisplayNameCollision("bumble", counts), true);
+  assert.equal(hasVisibleDisplayNameCollision("Fizz", counts), false);
+});
 
 const summary = (over = {}) => ({
   displayName: "Ada",
diff --git a/desktop/src/features/profile/lib/identity.ts b/desktop/src/features/profile/lib/identity.ts
index d2e0a4fdd..ae7594284 100644
--- a/desktop/src/features/profile/lib/identity.ts
+++ b/desktop/src/features/profile/lib/identity.ts
@@ -191,3 +191,48 @@ export function formatOwnerLabel(
     truncatePubkey(ownerPubkey)
   );
 }
+
+/**
+ * Appends an agent's owner to a display name only when that name collides with
+ * another visible result. The returned label is presentation-only; callers
+ * keep the original display name for selection and mention insertion.
+ */
+export function formatDisambiguatedAgentName(input: {
+  displayName: string;
+  hasNameCollision: boolean;
+  isAgent?: boolean;
+  ownerLabel?: string | null;
+}) {
+  const { displayName, hasNameCollision, isAgent, ownerLabel } = input;
+  const normalizedOwnerLabel = ownerLabel?.trim();
+
+  if (!hasNameCollision || !isAgent || !normalizedOwnerLabel) {
+    return displayName;
+  }
+
+  return `${displayName} (${normalizedOwnerLabel})`;
+}
+
+/** Case-insensitive display-name counts for a currently visible result set. */
+export function countVisibleDisplayNames(
+  displayNames: readonly (string | null | undefined)[],
+) {
+  const counts = new Map<string, number>();
+
+  for (const displayName of displayNames) {
+    const normalizedName = displayName?.trim().toLowerCase();
+    if (!normalizedName) {
+      continue;
+    }
+    counts.set(normalizedName, (counts.get(normalizedName) ?? 0) + 1);
+  }
+
+  return counts;
+}
+
+export function hasVisibleDisplayNameCollision(
+  displayName: string,
+  counts: ReadonlyMap<string, number>,
+) {
+  return (counts.get(displayName.trim().toLowerCase()) ?? 0) > 1;
+}
diff --git a/desktop/tests/e2e/ambiguous-agent-owner-suffix.spec.ts b/desktop/tests/e2e/ambiguous-agent-owner-suffix.spec.ts
new file mode 100644
index 000000000..bde622acf
--- /dev/null
+++ b/desktop/tests/e2e/ambiguous-agent-owner-suffix.spec.ts
@@ -0,0 +1,151 @@
+import { expect, test } from "@playwright/test";
+
+import {
+  installMockBridge,
+  openNewMessagePage,
+  TEST_IDENTITIES,
+} from "../helpers/bridge";
+import { waitForAnimations } from "../helpers/animations";
+
+const SHOTS = "test-results/ambiguous-agent-owner-suffix";
+const CURRENT_OWNER_PUBKEY = "deadbeef".repeat(8);
+const FIRST_AGENT_PUBKEY = "1010".repeat(16);
+const SECOND_AGENT_PUBKEY = "2020".repeat(16);
+
+const duplicateAgentOptions = {
+  relayAgents: [
+    {
+      pubkey: FIRST_AGENT_PUBKEY,
+      name: "Echo",
+      respondTo: "allowlist" as const,
+      respondToAllowlist: [CURRENT_OWNER_PUBKEY],
+    },
+    {
+      pubkey: SECOND_AGENT_PUBKEY,
+      name: "eChO",
+      respondTo: "allowlist" as const,
+      respondToAllowlist: [CURRENT_OWNER_PUBKEY],
+    },
+  ],
+  searchProfiles: [
+    {
+      pubkey: FIRST_AGENT_PUBKEY,
+      displayName: "Echo",
+      ownerPubkey: CURRENT_OWNER_PUBKEY,
+      isAgent: true,
+    },
+    {
+      pubkey: SECOND_AGENT_PUBKEY,
+      displayName: "eChO",
+      ownerPubkey: TEST_IDENTITIES.outsider.pubkey,
+      isAgent: true,
+    },
+  ],
+};
+
+test("captures duplicate agent names in mention autocomplete", async ({
+  page,
+}) => {
+  await installMockBridge(page, duplicateAgentOptions);
+  await page.goto("/");
+  await page.getByTestId("channel-general").click();
+  await page.getByTestId("message-input").fill("@echo");
+
+  const autocomplete = page
+    .getByTestId("message-composer")
+    .getByTestId("mention-autocomplete");
+  const firstRow = autocomplete.getByTestId(
+    `mention-suggestion-${FIRST_AGENT_PUBKEY}`,
+  );
+  const secondRow = autocomplete.getByTestId(
+    `mention-suggestion-${SECOND_AGENT_PUBKEY}`,
+  );
+  await expect(firstRow.getByTestId("mention-suggestion-name")).toHaveText(
+    "Echo (you)",
+  );
+  await expect(secondRow.getByTestId("mention-suggestion-name")).toHaveText(
+    "eChO (outsider)",
+  );
+  await expect(firstRow).toContainText("owned by you");
+  await expect(secondRow).toContainText("owned by outsider");
+
+  await waitForAnimations(page);
+  await autocomplete.screenshot({ path: `${SHOTS}/after-mention.png` });
+});
+
+test("captures duplicate agent names in add-member results", async ({
+  page,
+}) => {
+  await installMockBridge(page, duplicateAgentOptions);
+  await page.goto("/");
+  await page.getByTestId("channel-general").click();
+  await page.getByTestId("channel-members-trigger").click();
+  await page.getByTestId("channel-management-search-users").fill("echo");
+
+  const firstRow = page.getByTestId(
+    `channel-user-search-result-${FIRST_AGENT_PUBKEY}`,
+  );
+  const secondRow = page.getByTestId(
+    `channel-user-search-result-${SECOND_AGENT_PUBKEY}`,
+  );
+  await expect(
+    firstRow.getByTestId("channel-user-search-result-name"),
+  ).toHaveText("Echo (you)");
+  await expect(
+    secondRow.getByTestId("channel-user-search-result-name"),
+  ).toHaveText("eChO (outsider)");
+  await expect(
+    firstRow.getByRole("button", { name: "Select Echo (you)", exact: true }),
+  ).toBeVisible();
+  await expect(
+    secondRow.getByRole("button", {
+      name: "Select eChO (outsider)",
+      exact: true,
+    }),
+  ).toBeVisible();
+  await expect(firstRow).toContainText("owned by you");
+  await expect(secondRow).toContainText("owned by outsider");
+
+  await waitForAnimations(page);
+  await page
+    .getByTestId("members-sidebar-people")
+    .screenshot({ path: `${SHOTS}/after-add-member.png` });
+});
+
+test("captures duplicate agent names in new-message results", async ({
+  page,
+}) => {
+  await installMockBridge(page, duplicateAgentOptions);
+  await page.goto("/");
+  await openNewMessagePage(page);
+  await page.getByTestId("new-dm-search").fill("echo");
+
+  const firstRow = page.getByTestId(`new-dm-result-${FIRST_AGENT_PUBKEY}`);
+  const secondRow = page.getByTestId(`new-dm-result-${SECOND_AGENT_PUBKEY}`);
+  await expect(
+    firstRow
+      .getByTestId(`new-dm-name-${FIRST_AGENT_PUBKEY}`)
+      .getByText("Echo (you)", { exact: true }),
+  ).toBeVisible();
+  await expect(
+    secondRow
+      .getByTestId(`new-dm-name-${SECOND_AGENT_PUBKEY}`)
+      .getByText("eChO (outsider)", { exact: true }),
+  ).toBeVisible();
+  await expect(
+    page.getByRole("option", { name: "Add Echo (you)", exact: true }),
+  ).toBeVisible();
+  await expect(
+    page.getByRole("option", {
+      name: "Add eChO (outsider)",
+      exact: true,
+    }),
+  ).toBeVisible();
+  await expect(firstRow).toContainText("owned by you");
+  await expect(secondRow).toContainText("owned by outsider");
+
+  await waitForAnimations(page);
+  await page
+    .getByTestId("new-message-recipient-popover")
+    .screenshot({ path: `${SHOTS}/after-new-message.png` });
+});