[Bug]: send near-max leaves unspendable dust change

[piotr-iohk]

What happened?

When sending near-max on-chain from a wallet with 40,000 sats, sending 39,500 sats leaves 359 sats as change.
That remaining change is dust and cannot be spent.

Expected behavior

No unspendable dust should be left after send.
If the leftover change would be dust, it should be added to either the recipient amount or the fee, and the UI should clearly inform the user how dust is handled.

Steps to Reproduce

1. Fund wallet with 40,000 sats.
2. Create an on-chain send for 39,500 sats.
3. Confirm and broadcast transaction.
4. Observe remaining wallet balance is 359 sats (unspendable dust).

Logs / Screenshots / Recordings

logs.zip

Screen.Recording.2026-03-02.at.10.22.01.mov

Bitkit Version

2.0.3 (master at eeb6511039c26b614b0ca07269ced9c690c626be)

Device / OS

Android Emulator Pixel_6 (sdk_gphone64_arm64), Android 13 (API 33)

Reproducibility

Always

Additional context

• Current behavior differs from iOS handling tracked in bitkit-ios#200.
• Cross-platform behavior should be consistent for dust handling in near-max sends.
• Desired UX: if dust is absorbed into fee or recipient, explicitly surface that to the user.
• Current observed minimum spendable amount from wallet is 547 sats (+ fees); this likely reflects a dust threshold, so leaving 359 sats change results in effectively unspendable funds.

Similar issues check

• bitkit-android#616 — Failed to load utxos in manual coin selection — OPEN
  Failed to load utxos in manual coin selection #616
  Not a duplicate (manual UTXO loading issue, different symptom).
• bitkit-android#645 — Can request to receive less than dust onchain — OPEN
  [Bug]: Can request to receive less than dust onchain #645
  Not a duplicate (receive-flow dust threshold issue, not send/change dust).
• bitkit-android#324 — Insufficient funds when trying to send all funds — CLOSED
  InsufficientFunds='The available funds are insufficient to complete the given operation' when trying to send all funds #324
  Related but not equivalent; this report is specifically about creating unspendable dust change after near-max send.
• bitkit-ios#200 — Coin selection failed when sending near max amount from the wallet — OPEN
  Coin selection failed when sending near max amount from the wallet bitkit-ios#200
  Related cross-platform behavior reference.