dual-copy problem with browser exports

[marcelosalloum]

Describe the bug
@stellar/js-stellar-sdk has a a dual-copy problem within the same version:

1. Copy A — The browser bundle (dist/stellar-sdk.min.js) is a self-contained UMD webpack bundle. It inlines @stellar/stellar-base@14.0.4's own browser dist inside itself. When one calls import { TransactionBuilder } from "@stellar/stellar-sdk" in a browser build, esbuild resolves the "browser" export condition and pulls in this bundle. The Transaction class from this embedded copy is what TransactionBuilder.build() returns.
2. Copy B — The "./rpc" subpath export has no "browser" condition — it always resolves to ./lib/rpc/index.js. That CJS file does require("@stellar/stellar-base"), which resolves to the standalone @stellar/stellar-base@14.0.4 package in node_modules. This is a separate module instance with its own Transaction class.

This resulted in an error being thrown by a mismatched instance (instanceof): Copy A's TransactionBuilder.build() returns a Transaction from the browser-embedded stellar-base, then Copy B's assembleTransaction() (from ./lib/rpc/) calls TransactionBuilder.cloneFrom() which checks instanceof against the standalone stellar-base's Transaction. Same version, same code, but two distinct module instances — instanceof returns false, and an error is thrown.

Suggested solution

This seems to be a bug in @stellar/stellar-sdk's export map. The ./rpc and /contract subpath exports should either:

• Have their own "browser" condition pointing into the UMD bundle; or
• The root . export should not have a "browser" condition that diverges from the lib/ tree

What version are you on?
14.5.0

Expected behavior
instanceof should succeed