### 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_
{
    LOCK(cs_desc_man);
    if (m_storage.IsLocked() || m_storage.IsWalletFlagSet(WALLET_FLAG_LAST_HARDENED_XPUB_CACHED)) {
        return;
    }
    
    if (m_wallet_descriptor.cache.GetCachedLastHardenedExtPubKeys().size() > 0) {
        return;
    }
    
    FlatSigningProvider provider;
    provider.keys = GetKeys();
    FlatSigningProvider out_keys;
    std::vector<CScript> scripts_temp;
    DescriptorCache temp_cache;
    if (!m_wallet_descriptor.descriptor->Expand(0, provider, scripts_temp, out_keys, &temp_cache)){
        throw std::runtime_error("Unable to expand descriptor");
    }
    
    DescriptorCache diff = m_wallet_descriptor.cache.MergeAndDiff(temp_cache);
    if (!WalletBatch(m_storage.GetDatabase()).WriteDescriptorCacheItems(GetID(), diff)) {
        throw std::runtime_error(std::string(__func__) + ": writing cache items failed");
    }
}
void DescriptorScriptPubKeyMan::UpdateWalletDescriptor(WalletDescriptor& descriptor)