Dust Attack Protection: Classification of Already-Spent Dust & Descendant UTXO Marking

[Parsh]

Context

Part of #6965 — Dust Attack Protection and Donate Dust.

This issue covers the case where a potential dust UTXO was already spent before Keeper could mark it Do Not Spend. In that case, Keeper should trace the current wallet-owned descendant UTXOs of that spend and mark them Do Not Spend. It also covers labelling the spending transaction in transaction history. See also:

• Dust Attack Protection: Classification of Unspent UTXOs (Automatic & Manual) #6970 — Dust Classification: Unspent UTXOs (Automatic & Manual)
• Dust Spend Restrictions & UTXO Management UI
• Dust Donation

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Goal

When Keeper scans wallet history and finds a UTXO that would have met the dust rules but was already spent, it should:

1. Mark the spending transaction as a Potential dust spend
2. Trace current wallet-owned descendant UTXOs from that spend
3. Mark all traceable current affected descendant UTXOs as Do Not Spend with reason: Linked to potential dust spend

This applies across descendant layers where traceable — not only one layer deep.

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Detection: Already-Spent Dust

A historical UTXO is considered potential dust if it would have met these rules at the time it was received:

• Amount under 5,000 sats, AND
• Received on a reused receive address, OR received on an out-of-order receive address, OR received on a reused change address

If such a UTXO was spent in a transaction, that transaction is a Potential dust spend.

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Descendant UTXO Marking

From the Potential dust spend transaction:

• Identify all current wallet-owned UTXOs that descended from that transaction (outputs that are still unspent and owned by this wallet)
• Trace through multiple layers where possible
• Mark each as Do Not Spend
• Reason: Linked to potential dust spend

These UTXOs should be classified in the same scan pass as normal dust classification.

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Scan Points

This classification runs during the same scan points as normal dust classification:

• wallet creation
• wallet import / restore
• wallet opened after app update (classify UTXOs without state)
• normal wallet refresh
• pull-to-refresh
• new incoming transaction scan

No separate global upgrade script is required.

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Transaction History Labels

Transaction list item: Show label Potential dust spend on the spending transaction.

Transaction detail:

Show explanation:

This transaction may have spent a suspicious small amount together with other wallet funds. This may have reduced wallet privacy.

This is informational only — no action is shown for the already-spent dust itself.

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Red Dot & UI Indicator Rules

• Show red dot on wallet card / More Options if there are current Do Not Spend coins that descended from a potential dust spend
• A historical Potential dust spend alone does not show a red dot if there are no current Do Not Spend descendant coins
• Includes Do Not Spend coins appears in Wallet Details if there are current Do Not Spend descendant coins

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UTXO Details for Linked Descendants

For a UTXO marked Do Not Spend due to a linked potential dust spend:

• Show reason: Linked to potential dust spend
• Show explanation: Keeper marked this coin Do Not Spend to help protect wallet privacy.
• Show button: Mark Spendable
• On action, persist override and stay on UTXO Details
• Success feedback: Coin marked spendable
• System-marked Do Not Spend cannot be removed like a normal label — user must use explicit CTA

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Acceptance Criteria

• Already-spent historical dust UTXO marks the spending transaction as Potential dust spend
• Current wallet-owned descendant UTXOs of that spend are marked Do Not Spend
• Descendant tracing applies across multiple layers where traceable
• Reason on descendant UTXOs reads: Linked to potential dust spend
• Classification runs during wallet creation, import/restore, app update open, normal refresh
• Transaction list shows Potential dust spend label on the spending transaction
• Transaction detail shows explanation about possible privacy impact
• No action is shown for the already-spent dust itself
• Red dot appears on wallet card only if there are current Do Not Spend descendant coins
• Includes Do Not Spend coins appears in Wallet Details only if current Do Not Spend descendant coins exist
• UTXO Details for a linked descendant shows Linked to potential dust spend as reason
• Mark Spendable override persists after refresh

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Copy Requirements

Use these exact labels:

• Do Not Spend
• Linked to potential dust spend (reason on UTXO)
• Potential dust spend (transaction label)
• Keeper marked this coin Do Not Spend to help protect wallet privacy.
• This transaction may have spent a suspicious small amount together with other wallet funds. This may have reduced wallet privacy.
• Mark Spendable
• Coin marked spendable

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Design Requirements

• Reuse existing transaction list item label/chip component
• Reuse existing transaction detail info/warning pattern
• Reuse existing UTXO label/chip component
• No new assets required
• Do not create a new dust history screen