### 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_
cls = cls * 3 + (pos >> 5); 
        if (++clscount == 3) {
            
            c = PolyMod(c, cls);
            cls = 0;
            clscount = 0;
        }
    }
    if (clscount > 0) c = PolyMod(c, cls);
    for (int j = 0; j < 8; ++j) c = PolyMod(c, 0); 
    c ^= 1; 
    std::string ret(8, ' ');
    for (int j = 0; j < 8; ++j) ret[j] = CHECKSUM_CHARSET[(c >> (5 * (7 - j))) & 31];
    return ret;
}
std::string AddChecksum(const std::string& str) { return str + "#" + DescriptorChecksum(str); }
typedef std::vector<uint32_t> KeyPath;
struct PubkeyProvider
{
protected:
    
    
    uint32_t m_expr_index;
public:
    explicit PubkeyProvider(uint32_t exp_index) : m_expr_index(exp_index) {}
    virtual ~PubkeyProvider() = default;
    /** Compare two public keys represented by this provider.
     * Used by the Miniscript descriptors to check for duplicate keys in the script.
     */
    bool operator<(PubkeyProvider& other) const {