fix(policy): don't expose signer or key material through enforced handles

[AlonzoRicardo]

Summary

The policy engine's enforced account (wdk.getAccount()) and its protocol proxies only substituted the named members (the OPERATIONS write methods, protocol verbs, simulate, registerProtocol). Every other property read fell through to the raw account via Reflect.get, so the guarded handle still surfaced:

• keyPair → the private key
• _signer → the raw signer (account._signer.signTransaction(...))
• _provider / _config
• a protocol's _account back-reference (account.getSwapProtocol(x)._account.sendTransaction(...))

Any of these lets a caller holding an "enforced" account sign or move funds without policy evaluation, defeating the guardrail the proxy exists to provide.

Fix

Both get traps now hide key material and internal references through one shared rule:

function isProtectedMember (prop) {
  return prop === 'keyPair' || (typeof prop === 'string' && prop.startsWith('_'))
}

• keyPair is blocked by name — it's the one public getter that returns key material.
• The underscore rule structurally covers _signer, _provider, _config, the ERC-4337 _ownerAccount, and a protocol's _account across every chain, rather than a per-name denylist that would miss chain-specific fields.
• The prototype-climb variant (Object.getPrototypeOf(account).sendTransaction.call(account, …)) is neutralized by the same rule: every signing path funnels through this._signer, now undefined.

Unchanged: enforced write methods, protocol getters, simulate, registerProtocol, all reads (getBalance, quotes, verify, …), and identity accessors (path, index). instanceof still holds (no getPrototypeOf trap). Ungoverned accounts (no policy registered) are untouched.

The wallet classes' public API is deliberately not changed — the boundary is enforced only at the proxy, so direct (non-governed) users keep keyPair/_signer (no # private fields introduced).

Scope / trust boundary

This contains a caller holding an enforced account. It is not a defense against code that also holds the WalletManager/WDK instance or constructs an account directly — that remains the existing, documented trust boundary.

Tests

New internal-reference containment block covering: keyPair hidden, _signer/_provider/_config hidden, reads + enforced ops still work, and the protocol _account reach-through blocked while protocol enforcement still holds. Full suite 135 passing, standard clean.