[ibrhmyi]

Closes #2423.

For a malformed (non-numeric) amount passed to hosted buildOrder/createOrder, the TypeScript SDK raised the same "amount must be positive" message it uses for a genuinely non-positive numeric amount (Number("garbage") is NaN, and NaN > 0 is false). The Python SDK distinguishes the two cases. This aligns TypeScript with Python's two-message scheme (the more informative of the two options in the issue):

Change

• sdks/typescript/pmxt/client.ts (_hostedBuildOrderBody): a finite-number guard now raises InvalidOrder("amount must be a finite positive number") for malformed/non-finite input before the existing positivity check; the amount must be positive branch is unchanged for finite <= 0 values
• Side effect: Infinity no longer leaks into to6dec (which died with "invalid amount: Infinity")

Tests

• New hosted buildOrder amount validation suite (5 cases: non-numeric string, negative, zero, NaN, Infinity) — the guard runs before any network/wallet access, so all reject locally
• RED on unmodified code: string/NaN threw the positivity message, Infinity threw the to6dec message (3 of 5 failing)
• Full TS SDK suite: 98 passed (baseline 93); tsc --noEmit clean

AI assistance was used for this contribution (implementation and review).