<think>
Okay, I need to implement two functions, unpack_crates and crate_depth, for handling nested shipping crates. Let me start by understanding the problem.

First, the unpack_crates function. The goal is to flatten a list of crates, where each crate can contain either items (strings) or nested crates. The items should be collected in order, going left to right. When encountering a nested crate, we need to process it recursively before moving on. Also, any invalid entry (not a string or list) should cause the function to reject the crate, returning an error. Wait, the problem says that the function should reject an entry that is neither a non-empty string nor a list. So, if any element in the crate is invalid, the entire crate is invalid. But how does that affect the unpack_crates? The problem says that unpack_crates returns every item name in a flat list, but if there's an invalid entry, it should count as an error. Wait, the problem says "It rejects an entry that is neither a non-empty string nor a list, counting the empty string as invalid, with an error." So, if any element in the crate is invalid (like an empty string or not a string/list), then the entire crate is invalid, and the function should return an error. But how is that handled? The function is supposed to return a list, but if there's an invalid entry, it should raise an error? Or maybe the function returns an empty list if there's an invalid entry? Wait, the problem says "It rejects an entry that is neither a non-empty string nor a list, counting the empty string as invalid, with an error." So, the function should check each element. If any element is invalid (not a string or list), then the function should raise an error. Wait, but the problem says "rejects an entry that is neither a non-empty string nor a list, counting the empty string as invalid, with an error." So, the function should check each element. If any element is not a non-empty string or a list, then it's invalid. So, during the unpacking process, if any element is invalid, the function should raise a ValueError. But how to check that?

So, for unpack_crates, the first step is to validate the crate. Each element in the crate must be either a non-empty string or a list. If any element is not one of these, then the function should raise a ValueError. Then, proceed to unpack all the items.

So, the approach for unpack_crates is:

1. Check if the crate is valid. For each element in the crate, check if it's a non-empty string or a list. If any element is invalid, raise ValueError.

2. Then, recursively process each element. If the element is a list, process it recursively, and collect all the items. If it's a string, add it to the result.

But wait, the problem says that the crate is a list whose entries are either items or nested crates. So, the crate is a list, and each element is either a string (non-empty) or a list. So, during the unpacking, we need to check each element in the crate. For example, if the crate is [ "item1", [ "item2", "item3" ] ], then the unpacked list is ["item1", "item2", "item3"].

But if any element is not a string or a list, like a number or None, then it's invalid. Also, the empty string is considered invalid. So, the check is: for each element in the crate, it must be a non-empty string or a list. So, for example, if an