Inference failure when conditionally swapping variable?

還沒有人認領這個 Issue。

Is the following expected? Why does inference fail at all?

```lua
local a, b = 5, 8
if a < b then
b, a = a, b
-- ^ Unknown: cannot infer type.
end
print("(" .. a .. ", " .. b .. ")")
```

Start by reproducing the conditional multiple-assignment example from the issue and inspect the inference path for `b, a = a, b`. Trace why the reassignment produces an unknown-type diagnostic, then verify that the snippet no longer reports the diagnostic while preserving the inferred types of `a` and `b`.

由索引模型根據 Issue 內容生成。