### 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_
{
        if (m_depths.empty()) return true;
        std::vector<bool> path;
        for (size_t pos = 0; pos < m_depths.size(); ++pos) {
            if (pos) ret += ',';
            while ((int)path.size() <= m_depths[pos]) {
                if (path.size()) ret += '{';
                path.push_back(false);
            }
            std::string tmp;
            if (!m_subdescriptor_args[pos]->ToStringHelper(arg, tmp, type, cache)) return false;
            ret += tmp;
            while (!path.empty() && path.back()) {
                if (path.size() > 1) ret += '}';
                path.pop_back();
            }
            if (!path.empty()) path.back() = true;
        }
        return true;
    }
public:
    TRDescriptor(std::unique_ptr<PubkeyProvider> internal_key, std::vector<std::unique_ptr<DescriptorImpl>> descs, std::vector<int> depths) :
        DescriptorImpl(Vector(std::move(internal_key)), std::move(descs), "tr"), m_depths(std::move(depths))
    {
        assert(m_subdescriptor_args.size() == m_depths.size());
    }
    std::optional<OutputType> GetOutputType() const override { return OutputType::BECH32M; }