Fix reactions targeting stale Linq messages

agent/channels/linq.ts

@@ -113,7 +113,15 @@ export default linqChannel({
             "react_to_message requires an active Linq conversation thread."
           );
         }
-        const messageId = context.thread.toJSON().currentMessage?.id;
+        // The thread is a persisted snapshot; auth identifies this incoming message.
+        const target = resolveLinqReplyTarget(
+          { kind: "current" },
+          session.session.auth
+        );
+        const messageId =
+          target?.conversationId === context.thread.id
+            ? target.messageId
+            : undefined;
         if (!messageId) {
           throw new Error("react_to_message requires a current Linq message.");
         }

tests/agent/channels/linq-message-delivery.test.ts

@@ -993,6 +993,77 @@ describe("Linq message delivery", () => {
     );
     expect(post).not.toHaveBeenCalled();
   });
+
+  it.each(["add", "remove"] as const)(
+    "%s targets the incoming message when the thread snapshot is stale",
+    async (operation) => {
+      const { addReaction, context, removeReaction } =
+        handlerContext("first-message");
+
+      await handleActionResult(
+        reactToMessageResult({ operation, type: "thumbs_up" }),
+        context,
+        sessionContext("linq-message", undefined, "latest-message")
+      );
+
+      const deliver = operation === "add" ? addReaction : removeReaction;
+      const unused = operation === "add" ? removeReaction : addReaction;
+      expect(deliver).toHaveBeenCalledExactlyOnceWith(
+        "linq:dm:chat-1",
+        "latest-message",
+        "thumbs_up"
+      );
+      expect(unused).not.toHaveBeenCalled();
+    }
+  );
+
+  it("reacts to the incoming message without a cached current message", async () => {
+    const { addReaction, context } = handlerContext(null);
+
+    await handleActionResult(
+      reactToMessageResult({ operation: "add", type: "thumbs_up" }),
+      context,
+      sessionContext()
+    );
+
+    expect(addReaction).toHaveBeenCalledExactlyOnceWith(
+      "linq:dm:chat-1",
+      "message-1",
+      "thumbs_up"
+    );
+  });
+
+  it("does not react to a cached message without an incoming message ID", async () => {
+    const { addReaction, context, removeReaction } = handlerContext();
+
+    await expect(
+      handleActionResult(
+        reactToMessageResult({ operation: "add", type: "thumbs_up" }),
+        context,
+        sessionContext("linq-message", undefined, null)
+      )
+    ).rejects.toThrow("react_to_message requires a current Linq message.");
+
+    expect(addReaction).not.toHaveBeenCalled();
+    expect(removeReaction).not.toHaveBeenCalled();
+  });
+
+  it("rejects an incoming reaction target from a different conversation", async () => {
+    const { addReaction, context, removeReaction } = handlerContext();
+    const session = sessionContext();
+    session.session.auth.current.attributes.conversationId = "linq:other-chat";
+
+    await expect(
+      handleActionResult(
+        reactToMessageResult({ operation: "add", type: "thumbs_up" }),
+        context,
+        session
+      )
+    ).rejects.toThrow("react_to_message requires a current Linq message.");
+
+    expect(addReaction).not.toHaveBeenCalled();
+    expect(removeReaction).not.toHaveBeenCalled();
+  });
 });
 
 function sendMessageResult(