<think>
Okay, I need to fix the vet_upgrade_path function in the given Python code. The problem is that the current code is comparing tags as strings instead of numerically. Also, there are some validation checks that need to be added to ensure the tags are in the correct format and the steps are properly structured.

First, let me understand the requirements. The tags are in the format of two dot-separated numbers, like line.point. Each part should be a plain decimal without leading zeros, except for zero itself. The comparison should be numerical, not lexicographical. So, for example, 2.9 should be considered less than 2.10, even though as strings, "2.10" comes after "2.9".

The current code uses string comparisons, which is why the issue occurs. So I need to parse the tags into numerical values for comparison. Also, the function needs to validate that each tag is correctly formatted.

Next, the validation checks. The problem says that the function should reject any tag that is not a string or doesn't match the exact form. So, for each step's tag and the installed tag, we need to check that they are valid.

So, the steps to take:

1. Parse the installed tag and each step's tag into numerical values. For example, "2.9" becomes (2, 9), and "2.10" becomes (2, 10). Then compare them numerically.

2. Validate that each tag is in the correct format. This includes checking that the tag is a string, has exactly two parts separated by a dot, and each part is a valid number without leading zeros (except for zero itself).

3. Check that each step in the steps list is a dictionary with 'tag' and 'requires' keys, and that the 'tag' and 'requires' are valid tags.

4. Ensure that the steps are processed in order, and that each step's tag is strictly greater than the current carried tag, and that the requires is less than or equal to the current carried tag.

Wait, the current code has:

if carried < step["requires"]:
    raise error

But that's comparing the carried tag (as a string) to the requires. But the problem says that the step is lawful only when the tag the device then carries is at least requires and strictly older than the step's tag.

Wait, the step is lawful if the current carried tag is at least requires (so carried >= requires) and strictly older than the step's tag (so carried < step's tag). So the step is valid if the current carried is >= requires and < step's tag.

But in the current code, the first check is if carried < step["requires"], which would be the case if the current carried is less than requires. But that's not correct. Wait, the step is lawful only when the carried is at least requires. So if the carried is less than requires, then the step is invalid. So the first check is if carried < requires, then raise error. But the current code is checking if carried < step["requires"], which is correct. Wait, the current code is:

if carried < step["requires"]:
    raise ValueError(...)

But that's checking if the current carried is less than the requires. But according to the problem, the step is lawful only when the carried is at least requires. So if the carried is less than requires, then the step is invalid. So that check is correct.

But the problem is that the current code is comparing the tags as strings, not numerically. So the first thing is to parse the tags into numerical values for comparison.

So, the first step is to create a helper function to parse a tag string into