### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current behaviour

I randomly encountered this by loading a wallet created from master with an older version. I could trace it down to bd13dc2f46ea10302a928fcf0f53b7aed77ad260 (#26076), but I don't know descriptor wallets enough to understand what's going on (cc @Sjors @achow101).

### Expected behaviour

`bitcoind` starts, or at least tells me to use a later version if #26076 was a breaking change instead of corrupting `wallet.dat`.

### Steps to reproduce

(master, clean chain): 
`createwallet -regtest ""`
(v25.0rc2):
first `bitcoind -regtest` succeeds
then stop and restart the node: The second `bitcoind -regtest` leads to an InitError:
`Error: Error: Unable to expand wallet descriptor from cache`
now, the wallet cannot be loaded by either version.

### Relevant log output

_No response_

### How did you obtain Bitcoin Core

Compiled from source

### What version of Bitcoin Core are you using?

v25.0rc2 / master

### Operating system and version

Ubuntu

### Machine specifications

_No response_
bool KeyCompare(const Key& a, const Key& b) const {
        return *m_keys.at(a) < *m_keys.at(b);
    }
    template<typename I> std::optional<Key> FromString(I begin, I end) const
    {
        assert(m_out);
        Key key = m_keys.size();
        auto pk = ParsePubkey(key, {&*begin, &*end}, ParseScriptContext::P2WSH, *m_out, m_key_parsing_error);
        if (!pk) return {};
        m_keys.push_back(std::move(pk));
        return key;
    }
    std::optional<std::string> ToString(const Key& key) const
    {
        return m_keys.at(key)->ToString();
    }
    template<typename I> std::optional<Key> FromPKBytes(I begin, I end) const