fix(runtime): isolate channel messages by target

tauri/src/runtime/coordination/lineup-runtime.test.ts

@@ -379,6 +379,27 @@ describe("LineUpRuntime", () => {
     ]);
   });
 
+  it("ignores channel messages addressed to another user before scope routing", async () => {
+    const foreign = agentEnvelope("foreign-user-message", "lineup:2:channel_1:user_2", {
+      target: { kind: "human", id: "user_2" },
+    });
+    const own = agentEnvelope("current-user-message", "lineup:2:channel_1:user_1", {
+      target: { kind: "human", id: "user_1" },
+    });
+    const transport = new FakeTransport([[
+      { message_seq: 40, from_uid: "agent_1", payload: foreign },
+      { message_seq: 41, from_uid: "agent_1", payload: own },
+    ], []]);
+    const runtime = new LineUpRuntime({ storage: new MemoryStorage(), createTransport: () => transport });
+    const chat = runtime.openChatApp();
+    await runtime.login(login);
+    await runtime.syncOnce();
+
+    expect(chat.listAgentMessages()).toHaveLength(1);
+    expect(chat.listAgentMessages()[0]?.message_id).toBe("current-user-message");
+    expect(runtime.snapshot()?.cursor).toBe(41);
+  });
+
   it("rejects malformed scope and never delivers the same message id twice", async () => {
     const conversationID = "user_1:2:channel_1";
     const duplicate = agentEnvelope("dedupe_me", conversationID);

tauri/src/runtime/coordination/lineup-runtime.ts

@@ -754,6 +754,16 @@ export class LineUpRuntime {
       runtimeLog("message.ignored", { stage: "sender" });
       return;
     }
+    // The AppServer channel is shared by several users. Agent envelopes carry
+    // the intended human target; discard another user's message before scope
+    // validation so it is not reported as a malformed message for this user.
+    const parsedEnvelope = parseEnvelopeJSON(payload);
+    if (parsedEnvelope.ok
+      && parsedEnvelope.envelope.target?.kind === "human"
+      && parsedEnvelope.envelope.target.id !== this.session.uid) {
+      runtimeLog("message.ignored", { stage: "target" });
+      return;
+    }
     if (message.from_uid === this.session.uid) {
       const own = parseEnvelopeJSON(payload);
       if (own.ok && CONTROL_ECHO_TYPES.has(own.envelope.type)) return;