### 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_
{
    std::vector<CScript> dummy;
    FlatSigningProvider out;
    InferDescriptor(spk, provider)->Expand(0, DUMMY_SIGNING_PROVIDER, dummy, out);
    std::vector<CKeyID> ret;
    ret.reserve(out.pubkeys.size());
    for (const auto& entry : out.pubkeys) {
        ret.push_back(entry.first);
    }
    return ret;
}
void LegacyScriptPubKeyMan::MarkPreSplitKeys()
{
    WalletBatch batch(m_storage.GetDatabase());
    for (auto it = setExternalKeyPool.begin(); it != setExternalKeyPool.end();) {
        int64_t index = *it;
        CKeyPool keypool;
        if (!batch.ReadPool(index, keypool)) {
            throw std::runtime_error(std::string(__func__) + ": read keypool entry failed");
        }
        keypool.m_pre_split = true;
        if (!batch.WritePool(index, keypool)) {
            throw std::runtime_error(std::string(__func__) + ": writing modified keypool entry failed");
        }
        set_pre_split_keypool.insert(index);
        it = setExternalKeyPool.erase(it);
    }
}
bool LegacyScriptPubKeyMan::AddCScript(const CScript& redeemScript)