diff --git a/web/src/features/messages/ConversationView.tsx b/web/src/features/messages/ConversationView.tsx
index adf58de1..3eec38a4 100644
--- a/web/src/features/messages/ConversationView.tsx
+++ b/web/src/features/messages/ConversationView.tsx
@@ -35,6 +35,7 @@ import {
   closeConversation,
   ensureTopicAttached,
   forgetTopic,
+  getP2PPeerUserId,
   markConfirmedRead,
   openConversation,
   setActiveConversationTopic,
@@ -463,16 +464,23 @@ export function ConversationView() {
   // `['me']` key NavRail/ChatListColumn/SettingsLayout already keep warm, so this is a cache read in
   // the normal case, not a new request.
   const meQuery = useQuery({ queryKey: ['me'], queryFn: getMe });
+  // NOT topicId -- see getP2PPeerUserId's own doc comment. A P2P topic with any real history is
+  // addressed by a real, opaque `p2p...` name, not the peer's `usr...` id (that only holds true in
+  // the brief window before the very first subscribe) -- confirmed live: without this, this query
+  // 404s (`GET /users/{p2p...}/profile`) for every established conversation, and only ever appeared
+  // to work in earlier testing because that test happened to use a conversation opened for the first
+  // time in the same session, before the SDK's own rename kicked in.
+  const peerUserId = !isGroup && !isSelf && topicId ? getP2PPeerUserId(tinode.getTopic(topicId), myUserId) : undefined;
   // Real gap this was written to close: the chat header/message-row avatars only ever drew the
   // letter-tile fallback, even after a real custom avatar was uploaded and correctly showing up on
   // the contacts pages (FriendProfileView/ContactsListColumn) -- those read this exact same REST
   // profile, the conversation screen just never fetched it. Same query DetailColumn already runs
-  // (`['user-profile', topicId]`), so this dedupes with it whenever the detail panel happens to be
+  // (`['user-profile', peerUserId]`), so this dedupes with it whenever the detail panel happens to be
   // open, and only fetches for a real P2P peer, never for a group or `slf`.
   const peerProfileQuery = useQuery({
-    queryKey: ['user-profile', topicId],
-    queryFn: () => getUserProfile(topicId || ''),
-    enabled: !!topicId && !isGroup && !isSelf,
+    queryKey: ['user-profile', peerUserId],
+    queryFn: () => getUserProfile(peerUserId || ''),
+    enabled: !!peerUserId,
   });
   const membersQuery = useQuery({
     queryKey: ['group-members', topicId],
@@ -525,6 +533,11 @@ export function ConversationView() {
   const myAvatarFileId = meQuery.data?.profile.avatar_file_id;
   const peerAvatarFileId = isSelf ? myAvatarFileId : peerProfileQuery.data?.avatar_file_id;
   const headerAvatarFileId = isGroup ? groupProfileQuery.data?.avatar_file_id : peerAvatarFileId;
+  // Color-hash id, not the file lookup above -- topicId is right for a group (its own identity), but
+  // for P2P this should be the peer's stable usr id (peerUserId), matching the same hash ContactsListColumn/
+  // FriendProfileView use for this same person, rather than the p2p topic name (which isP2P/self also
+  // never had a usr-shaped id for in the first place).
+  const headerAvatarId = isGroup ? topicId : peerUserId || topicId;
   // `peerName` is the GROUP's own name for a group topic, not any member's -- reusing it to label
   // "who is being quoted" (as both the reply-composer preview and the actual sent quote block used
   // to) meant every single group-chat reply permanently displayed "回复 <群名>：…" for every member,
@@ -824,7 +837,7 @@ export function ConversationView() {
                 <Icon name="arrow_back_ios_new" />
               </Link>
               <button type="button" onClick={onToggleDetail} className="flex items-center gap-2.5 text-left">
-                <Avatar id={topicId} name={peerName} avatarFileId={headerAvatarFileId} className="h-9.5 w-9.5 flex-none rounded-lg text-sm" />
+                <Avatar id={headerAvatarId} name={peerName} avatarFileId={headerAvatarFileId} className="h-9.5 w-9.5 flex-none rounded-lg text-sm" />
                 <div className="flex flex-col">
                   <strong className="text-base font-semibold text-text-heading">
                     {peerName}
diff --git a/web/src/features/messages/DetailColumn.tsx b/web/src/features/messages/DetailColumn.tsx
index 8bb29d52..be9b66aa 100644
--- a/web/src/features/messages/DetailColumn.tsx
+++ b/web/src/features/messages/DetailColumn.tsx
@@ -21,9 +21,11 @@ import {
 import type { MediaType } from '@/lib/api/messages';
 import { getMe } from '@/lib/api/profile';
 import { useTinode } from '@/lib/tinode/hooks';
+import { getP2PPeerUserId } from '@/lib/tinode/topics';
 import { useCallStore } from '@/stores/calls';
 import { requestConfirm } from '@/stores/confirmDialog';
 import { notify } from '@/stores/globalToast';
+import { useSessionStore } from '@/stores/session';
 
 interface DetailColumnProps {
   topicId: string;
@@ -81,11 +83,24 @@ export function DetailColumn({ topicId, peerName, onClose, onOpenHistory }: Deta
   // error, confirmed live: this used to render "加入黑名单"/"投诉举报"/"删除好友" for your own notes
   // to yourself.
   const isSelf = topicId === 'slf';
+  const myUserId = useSessionStore((s) => s.myUserId);
+  // NOT topicId -- see getP2PPeerUserId's own doc comment. Every lookup below that means "the other
+  // user" (profile, friends-list match, block, remark) has to go through this, not the raw topic id,
+  // because the two stop being interchangeable the instant this conversation has any real history.
+  const peerUserId = isSelf ? topicId : getP2PPeerUserId(tinode.getTopic(topicId), myUserId);
 
   const friendsQuery = useQuery({ queryKey: ['friends'], queryFn: () => fetchAllPages((cursor) => getFriends('', cursor)) });
-  const friend = friendsQuery.data?.find((f) => f.user_id === topicId);
+  const friend = friendsQuery.data?.find((f) => f.user_id === peerUserId);
 
-  const profileQuery = useQuery({ queryKey: ['user-profile', topicId], queryFn: () => getUserProfile(topicId), enabled: !isSelf });
+  const profileQuery = useQuery({
+    queryKey: ['user-profile', peerUserId],
+    queryFn: () => getUserProfile(peerUserId || ''),
+    // `!isSelf` alone isn't enough now that peerUserId can genuinely be undefined for a beat (the
+    // subscriber list not loaded yet) -- without also gating on it, this fires with `undefined` the
+    // instant isSelf is false, same class of guaranteed-404 bug this whole fix targets, just with
+    // the literal string "undefined" as the id instead of the p2p topic name.
+    enabled: !isSelf && !!peerUserId,
+  });
   const idLine = [profileQuery.data?.public_account && `ID：${profileQuery.data.public_account}`, profileQuery.data?.region]
     .filter(Boolean)
     .join(' · ');
@@ -110,7 +125,7 @@ export function DetailColumn({ topicId, peerName, onClose, onOpenHistory }: Deta
   });
 
   const remarkMutation = useMutation({
-    mutationFn: (remark: string) => updateFriendRemark(topicId, remark),
+    mutationFn: (remark: string) => updateFriendRemark(peerUserId, remark),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['friends'] });
       setRemarkEditing(false);
@@ -119,16 +134,16 @@ export function DetailColumn({ topicId, peerName, onClose, onOpenHistory }: Deta
   });
 
   const blockMutation = useMutation({
-    mutationFn: (blocked: boolean) => (blocked ? blockUser(topicId) : unblockUser(topicId)),
+    mutationFn: (blocked: boolean) => (blocked ? blockUser(peerUserId) : unblockUser(peerUserId)),
     onSuccess: () => queryClient.invalidateQueries({ queryKey: ['blocks'] }),
     onError: (err) => showError(err, '设置失败，请重试'),
   });
 
   const blocksQuery = useQuery({ queryKey: ['blocks'], queryFn: () => fetchAllPages((cursor) => getBlocks(cursor)) });
-  const isBlocked = !!blocksQuery.data?.some((b) => b.user.user_id === topicId);
+  const isBlocked = !!blocksQuery.data?.some((b) => b.user.user_id === peerUserId);
 
   const deleteFriendMutation = useMutation({
-    mutationFn: () => deleteFriend(topicId),
+    mutationFn: () => deleteFriend(peerUserId),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['friends'] });
       navigate('/messages');
@@ -162,7 +177,7 @@ export function DetailColumn({ topicId, peerName, onClose, onOpenHistory }: Deta
       </header>
 
       <div className="flex flex-col items-center gap-1 border-b border-border-list-item px-5 pb-4 pt-6">
-        <Avatar id={topicId} name={peerName} avatarFileId={avatarFileId} className="h-18 w-18 rounded-2xl text-2xl" />
+        <Avatar id={peerUserId || topicId} name={peerName} avatarFileId={avatarFileId} className="h-18 w-18 rounded-2xl text-2xl" />
         <strong className="mt-2 text-[17px] font-semibold text-text-heading">{peerName}</strong>
         {idLine ? <span className="text-xs text-text-tertiary-2">{idLine}</span> : null}
         {profileQuery.data?.signature ? (
diff --git a/web/src/lib/tinode/tinode-sdk.d.ts b/web/src/lib/tinode/tinode-sdk.d.ts
index eef6489a..c8b8d9af 100644
--- a/web/src/lib/tinode/tinode-sdk.d.ts
+++ b/web/src/lib/tinode/tinode-sdk.d.ts
@@ -33,6 +33,18 @@ declare module 'tinode-sdk' {
     params?: Record<string, unknown>;
   }
 
+  /** One entry from `Topic#subscribers()` -- fields confirmed live against a real P2P topic (only
+   *  `user` is actually consumed anywhere in this app so far; the rest are declared for completeness). */
+  export interface Subscription {
+    user: string;
+    online?: boolean;
+    updated?: Date;
+    read?: number;
+    recv?: number;
+    acs?: { want?: string; given?: string; mode?: string };
+    public?: TopicDescPublic | null;
+  }
+
   export interface CredentialParam {
     meth: string;
     val?: string;
@@ -191,6 +203,20 @@ declare module 'tinode-sdk' {
     isSelfType(): boolean;
     getAccessMode(): AccessMode | undefined;
 
+    /**
+     * Iterates this topic's cached subscriber list, one `Subscription` per call -- for a P2P topic
+     * this is always exactly the two participants (self included), confirmed live. This is the only
+     * reliable way to recover the OTHER party's real `usr...` id once a P2P topic has been subscribed
+     * at least once: the SDK renames a freshly-addressed `usr...` topic to a real, opaque `p2p...`
+     * name the moment `subscribe()` succeeds (see topics.ts's `openConversation`), and -- confirmed by
+     * reading tinode.dev.js -- `Topic.topicType()`'s own prefix table has no `p2p` entry at all (only
+     * `usr` maps to the P2P type), so `isP2PType()`/`p2pPeerDesc()` silently stop working the instant
+     * a topic has this real name. `topic.name` itself is NOT a usable substitute for the peer's id
+     * past that point -- anything needing "the other user" (profile lookup, friends-list matching,
+     * block/remark) must go through this method instead.
+     */
+    subscribers(callback: (sub: Subscription) => void): void;
+
     /**
      * Iterates locally-cached messages in `[sinceId, beforeId]` (both omitted = everything cached).
      * `callback(msg, prevMsg, nextMsg, bufferIndex)` fires once per message, already resolved to the
diff --git a/web/src/lib/tinode/topics.ts b/web/src/lib/tinode/topics.ts
index 8ba30414..84e4e08b 100644
--- a/web/src/lib/tinode/topics.ts
+++ b/web/src/lib/tinode/topics.ts
@@ -38,6 +38,37 @@ export function getActiveConversationTopic(): string | null {
   return activeConversationTopic;
 }
 
+/**
+ * The other party's real `usr...` id for a P2P conversation -- NOT the same as `topic.name` once a
+ * conversation has any real history. Real, live-confirmed bug this fixes: a P2P topic addressed by
+ * the peer's own `usr...` id (the only address that exists before the very first subscribe -- e.g.
+ * straight from a friend's profile) gets renamed by the SDK to a real, opaque `p2p...` name the
+ * instant `subscribe()` succeeds (see openConversation's own doc comment on this same rename). Every
+ * P2P conversation with actual history is addressed by this `p2p...` form from then on -- but reading
+ * tinode.dev.js confirms `Topic.topicType()`'s prefix table has no `p2p` entry at all (only `usr` maps
+ * to the P2P type), so `topic.isP2PType()`/`topic.p2pPeerDesc()` silently return false/undefined for
+ * every one of these topics, and code that assumed "the P2P topic name IS the peer's user id" (true
+ * only for the brief pre-first-subscribe window) breaks the moment that assumption stops holding --
+ * confirmed live: `GET /users/{topicName}/profile` 404s, `friends.find(f => f.user_id === topicName)`
+ * never matches, block/remark/avatar all silently target a user id that doesn't exist.
+ *
+ * Returns `undefined` (never `topic.name` as a guess) when the subscriber list isn't populated yet --
+ * live-confirmed this matters: on the render right after navigating straight to a `p2p...`-named
+ * conversation, `subscribers()` can still be empty for the one or two renders before the subscribe
+ * response fills it in, and returning `topic.name` as a placeholder there just fires the exact same
+ * doomed `GET /users/{p2p...}/profile` request this function exists to prevent, a render later. Every
+ * caller already guards its query with `enabled: !!peerUserId`, so `undefined` correctly makes it wait
+ * instead of firing once with a value it knows is wrong.
+ */
+export function getP2PPeerUserId(topic: Topic, myUserId: string | null | undefined): string | undefined {
+  if (topic.name.startsWith('usr')) return topic.name;
+  let peer: string | undefined;
+  topic.subscribers((sub) => {
+    if (!peer && sub.user !== myUserId) peer = sub.user;
+  });
+  return peer;
+}
+
 const confirmedReadSeq = new Map<string, number>();
 
 /**