### 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 IsSingleType() const final { return true; }
};
/* We instantiate Miniscript here with a simple integer as key type.
 * The value of these key integers are an index in the
 * DescriptorImpl::m_pubkey_args vector.
 */
/**
 * The context for converting a Miniscript descriptor into a Script.
 */
class ScriptMaker {
    
    const std::vector<CPubKey>& m_keys;
public:
    ScriptMaker(const std::vector<CPubKey>& keys LIFETIMEBOUND) : m_keys(keys) {}
    std::vector<unsigned char> ToPKBytes(uint32_t key) const {
        return {m_keys[key].begin(), m_keys[key].end()};
    }
    std::vector<unsigned char> ToPKHBytes(uint32_t key) const {
        auto id = m_keys[key].GetID();
        return {id.begin(), id.end()};
    }
};
/**
 * The context for converting a Miniscript descriptor to its textual form.
 */
class StringMaker {