diff --git a/.changeset/fix-web-duplicate-user-message.md b/.changeset/fix-web-duplicate-user-message.md
new file mode 100644
index 0000000000..615fabee18
--- /dev/null
+++ b/.changeset/fix-web-duplicate-user-message.md
@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+web: Fix duplicate user message bubbles after a session snapshot resync.
diff --git a/apps/kimi-web/src/lib/snapshotMessages.ts b/apps/kimi-web/src/lib/snapshotMessages.ts
index 29b301ee6a..300008dc59 100644
--- a/apps/kimi-web/src/lib/snapshotMessages.ts
+++ b/apps/kimi-web/src/lib/snapshotMessages.ts
@@ -18,9 +18,23 @@ export function mergeSnapshotMessages(
   const earliestSnapshotMs = Date.parse(snapshot[0]!.createdAt);
   if (Number.isNaN(earliestSnapshotMs)) return snapshot;
 
+  // The optimistic bubble keeps its client-side id to avoid remounting, while
+  // submitPrompt stamps the authoritative v2 user-message id into promptId.
+  // Match that identity against the snapshot instead of guessing from content:
+  // repeated prompts are distinct messages even when their text/media is equal.
+  const snapshotIds = new Set(snapshot.map((m) => m.id));
+  const snapshotUserIds = new Set(snapshot.filter((m) => m.role === 'user').map((m) => m.id));
+
   const older = loaded.filter((message) => {
     const createdAtMs = Date.parse(message.createdAt);
-    return !Number.isNaN(createdAtMs) && createdAtMs < earliestSnapshotMs;
+    if (Number.isNaN(createdAtMs) || createdAtMs >= earliestSnapshotMs) return false;
+    if (snapshotIds.has(message.id)) return false;
+    if (
+      message.role === 'user' &&
+      message.promptId !== undefined &&
+      snapshotUserIds.has(message.promptId)
+    ) return false;
+    return true;
   });
 
   return older.length > 0 ? [...older, ...snapshot] : snapshot;
diff --git a/apps/kimi-web/test/lib-logic.test.ts b/apps/kimi-web/test/lib-logic.test.ts
index 1e7f3dc44e..7562f6cc0c 100644
--- a/apps/kimi-web/test/lib-logic.test.ts
+++ b/apps/kimi-web/test/lib-logic.test.ts
@@ -534,6 +534,40 @@ describe('mergeSnapshotMessages', () => {
     expect(mergeSnapshotMessages([], snapshot)).toBe(snapshot);
     expect(mergeSnapshotMessages(snapshot, [])).toEqual([]);
   });
+
+  function optimisticUser(id: string, createdAt: string, text: string, promptId: string): AppMessage {
+    return {
+      id,
+      sessionId: 's1',
+      role: 'user',
+      content: [{ type: 'text', text }],
+      createdAt,
+      promptId,
+      metadata: { 'kimiWeb.optimisticUserMessage': true },
+    };
+  }
+
+  function realUser(id: string, createdAt: string, text: string): AppMessage {
+    return {
+      id,
+      sessionId: 's1',
+      role: 'user',
+      content: [{ type: 'text', text }],
+      createdAt,
+    };
+  }
+
+  it('drops an optimistic user message when its promptId is the snapshot message id', () => {
+    const loaded = [optimisticUser('msg_opt_1', '2026-01-02T23:59:59.000Z', 'hello', 'msg_9')];
+    const snapshot = [realUser('msg_9', '2026-01-03T00:00:00.000Z', 'hello')];
+    expect(mergeSnapshotMessages(loaded, snapshot).map((m) => m.id)).toEqual(['msg_9']);
+  });
+
+  it('keeps an optimistic user message when a different snapshot message repeats its content', () => {
+    const loaded = [optimisticUser('msg_opt_1', '2026-01-02T23:59:59.000Z', 'hello', 'msg_8')];
+    const snapshot = [realUser('msg_9', '2026-01-03T00:00:00.000Z', 'hello')];
+    expect(mergeSnapshotMessages(loaded, snapshot).map((m) => m.id)).toEqual(['msg_opt_1', 'msg_9']);
+  });
 });
 
 describe('mergeSnapshotSubagents', () => {