### 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_
pubkeys.push_back(fullpubkey);
                }
            }
            for (const auto& pubkey : pubkeys) {
                std::unique_ptr<FlatSigningProvider> pk_keys = GetSigningProvider(pubkey);
                if (pk_keys) {
                    keys->Merge(std::move(*pk_keys));
                }
            }
        }
        SignPSBTInput(HidingSigningProvider(keys.get(), !sign, !bip32derivs), psbtx, i, &txdata, sighash_type, nullptr, finalize);
        bool signed_one = PSBTInputSigned(input);
        if (n_signed && (signed_one || !sign)) {
            
            
            
            (*n_signed)++;
        }
    }
    
    for (unsigned int i = 0; i < psbtx.tx->vout.size(); ++i) {
        std::unique_ptr<SigningProvider> keys = GetSolvingProvider(psbtx.tx->vout.at(i).scriptPubKey);
        if (!keys) {
            continue;
        }
        UpdatePSBTOutput(HidingSigningProvider(keys.get(), true, !bip32derivs), psbtx, i);
    }
    return TransactionError::OK;
}
std::unique_ptr<CKeyMetadata> DescriptorScriptPubKeyMan::GetMetadata(const CTxDestination& dest) const