refactor(shared): remove dead MoneyAmount twins (USD/JMD/BTC) [ENG-518]

[islandbitcoin]

Why

Follow-up to the cashout #449 → #450 saga. src/domain/shared/MoneyAmount.ts carried duplicate USDAmount / JMDAmount / BtcAmount classes that were dead — the @domain/shared barrel serves those from ./money (export * from "./money") and takes only USDTAmount from this file. That shadow twin is exactly what let #449's JMD-rate fix land on the wrong copy while cashout stayed broken; #450 fixed the live ./money/JMDAmount.ts.

Change

Strip the file to its only live exports — the base MoneyAmount + USDTAmount — and delete the dead USDAmount/JMDAmount/BtcAmount. MoneyAmount.from()/fromJSON() (used only by tests, only with USDT; the sole prod reference is commented out) are trimmed to the USDT branch. A header comment documents the split so no currency-amount class gets re-added here.

Verification

• tsc -p tsconfig.json --noEmit: clean project-wide — nothing referenced the deleted classes.
• Money.spec.ts: 22/22 — including the barrel-resolved JMDAmount fractional-rate regression (fix(cashout): decimal-safe JMD rate on the ACTUAL JMDAmount used by cashout #450), the USDAmount → JMDAmount conversion, and the base MoneyAmount.from(Usdt) / fromJSON round-trip that exercise the trimmed factory.

Closes ENG-518.

🤖 Generated with Claude Code

[linear]

ENG-518

[islandbitcoin]

Review — refactor(shared): remove dead MoneyAmount twins

Net: correct and safe. The deletion is verified — the removed USDAmount / JMDAmount / BtcAmount were never barrel-exported (the @domain/shared barrel does export * from "./money" and takes only { USDTAmount } from this file), nothing imports them from the file path, and tsc is clean project-wide. This is good, incident-preventing cleanup. Four findings — two already addressed in 0a7f2f1a6, two left as follow-ups.

A — [addressed in 0a7f2f1a6] The header comment was factually wrong. It claimed this file is "the canonical home of the base MoneyAmount." It isn't: the barrel exports ./money/MoneyAmount.ts as MoneyAmount, and this file's base is reached only via USDTAmount's inheritance plus one direct test import. A fix landing on the wrong MoneyAmount copy is exactly what this PR exists to prevent, so a comment asserting the wrong file is canonical is a landmine for the next debugger. Rewritten to describe the split accurately, including the instanceof consequence in B.

B — [open, tracked as ENG-523] The base-class duplication is still standing. There are two abstract class MoneyAmount in two files named MoneyAmount.ts, and they've diverged (./money's has abstract i18n() and a different asPaymentAmount() return type). Because USDTAmount extends this file's base and not the barrel's, x instanceof MoneyAmount (the barrel's) does not match a USDTAmount — see the live workaround at src/app/offers/storage/OffersSerde.ts:16 (value instanceof MoneyAmount || value instanceof USDTAmount). This PR removes the leaf twins but leaves the more dangerous base duplication. The real fix — USDTAmount implementing ./money's base and moving there, deleting this file, exporting everything from ./money, and dropping the || instanceof USDTAmount crutches — touches ~73 USDTAmount call sites and instanceof semantics, so it belongs in its own ticket, not this one. Tracked as ENG-523.

C — [open, author's call] from() / fromJSON() is now a one-type factory. After the trim it constructs only USDTAmount and returns UnsupportedCurrencyError for everything else, while ./money already provides toMoneyAmount / toMoneyAmountFromJSON for USD/JMD. It's not dead — it's the only generic USDT-JSON restore path (./money's factory deliberately doesn't handle USDT) — so keeping it is defensible, but a factory that makes exactly one thing is a smell. Worth deciding its fate alongside B.

D — [addressed in 0a7f2f1a6] The test reaches past the barrel. Money.spec.ts imports MoneyAmount from @domain/shared/MoneyAmount (the file, not the barrel) to hit this USDT-scoped base — the same deep coupling that made "which MoneyAmount?" ambiguous in the first place. Added a comment noting why it bypasses the barrel.

A and D are pushed in 0a7f2f1a6. B is tracked as ENG-523; C is your call.

[islandbitcoin]

Review dispositions — all four findings resolved

Thanks for the review. Closing out the loop so this is merge-ready:

• A (header comment was wrong) — ✅ fixed in 0a7f2f1a6.
• D (test reaches past the barrel) — ✅ commented in 0a7f2f1a6.
• B (base-class duplication still standing) — deferred to its own ticket, as you suggested: ENG-523. It's out of scope for a "delete dead code" PR — the real fix moves USDTAmount onto ./money's base and drops the || instanceof USDTAmount crutches across ~73 call sites. The header comment now points there explicitly (8b14004b: follow-up: ENG-523) so the next debugger lands on the ticket, not a bare "(follow-up)".
• C (from()/fromJSON() is a one-type factory) — keeping it, folded into ENG-523. It's not dead: it's the generic USDT-JSON restore entry (./money's toMoneyAmount/toMoneyAmountFromJSON deliberately skip USDT) and is exercised by Money.spec.ts; its only prod reference is commented out (payment-input-validator.ts:33). Removing or reshaping it means touching ./money's factory too, which is exactly the base-consolidation work in B — so its fate is decided there, not in this cleanup PR.

This PR satisfies ENG-518's second acceptance path ("keep the top-level file solely for base MoneyAmount + USDTAmount with a comment explaining the split"). CI is green project-wide. Ready to merge.