### 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_
error = strprintf("Provided checksum '%s' does not match computed checksum '%s'", std::string(check_split[1].begin(), check_split[1].end()), checksum);
            return false;
        }
    }
    if (out_checksum) *out_checksum = std::move(checksum);
    sp = check_split[0];
    return true;
}
std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out, std::string& error, bool require_checksum)
{
    Span<const char> sp{descriptor};
    if (!CheckChecksum(sp, require_checksum, error)) return nullptr;
    uint32_t key_exp_index = 0;
    auto ret = ParseScript(key_exp_index, sp, ParseScriptContext::TOP, out, error);
    if (sp.size() == 0 && ret) return std::unique_ptr<Descriptor>(std::move(ret));
    return nullptr;
}
std::string GetDescriptorChecksum(const std::string& descriptor)
{
    std::string ret;
    std::string error;
    Span<const char> sp{descriptor};
    if (!CheckChecksum(sp, false, error, &ret)) return "";
    return ret;
}
std::unique_ptr<Descriptor> InferDescriptor(const CScript& script, const SigningProvider& provider)
{
    return InferScript(script, ParseScriptContext::TOP, provider);
}
void DescriptorCache::CacheParentExtPubKey(uint32_t key_exp_pos, const CExtPubKey& xpub)