Problem

HTTPWalletWire accepts and stores an httpClient constructor parameter, but transmitToWallet calls the global fetch directly — so the injected client is silently dropped.

This makes it impossible to:

• wrap requests with AuthFetch for BRC-103 mutual authentication (auth headers are dropped → requests go out unauthenticated and are rejected by an auth-protected server);
• inject a custom fetch (timeouts/proxy/retries/headers) or a mock for testing.

The sibling substrate HTTPWalletJSON already uses its injected httpClient, so this is an inconsistency rather than intentional — it dates back to when the HttpClient abstraction was replaced with native fetch: the constructor parameter was kept and re-typed to typeof fetch, but the body was changed to call the global fetch(...) instead of this.httpClient(...).

Fix

transmitToWallet now calls this.httpClient instead of the global fetch. Because httpClient defaults to the global fetch, existing behavior is unchanged.

Tests

• Added a regression test asserting the injected client is used (and the global fetch is not). It fails without this fix and passes with it.
• Updated a stale comment and test name that documented the old behavior.
• All existing HTTPWalletWire tests pass (44/44).