staticaddr: fractional swap amount

[hieblmi]

This PR adds an amount flag to static loop-in swaps that allows the caller to only swap a fraction of the value of the selected deposits. If only amount is selected, the client selects deposits automatically to cover for the swaps amount.

To ensure backwards UX compatibility, omitting the new flag (--amount=0) selects the total deposit amount for swapping.

TODO

• Sign sweepless sweep with change output if needed
• integration test

[Copilot]

Pull Request Overview

This PR introduces support for fractional swap amounts in static loop‐in swaps by adding a new amount flag. Key changes include:

• Logic updates in the loop-in store, manager, and swap creation to use a user-specified amount if provided.
• Additions to the deposit and SQL layers to support lookup by outpoint and store the selected amount.
• Updates to the RPC protos and CLI to expose and handle the new amount flag.

Reviewed Changes

Copilot reviewed 19 out of 23 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
staticaddr/loopin/sql_store.go	Adjusts swap creation logic to set AmountRequested based on flag.
staticaddr/loopin/manager.go	Updates loop-in initiation and sweep handling to use selected amount.
staticaddr/loopin/loopin.go	Uses the selected amount for calculating swap and change outputs.
staticaddr/loopin/interface.go	Adds DepositsForOutpoints signature to retrieve deposits by outpoints.
staticaddr/loopin/actions.go	Adapts invoice and fee calculations based on the selected amount.
staticaddr/deposit/*	Introduces functions to retrieve deposits by outpoint.
looprpc/client.proto	Adds a new field for the swap amount in the loop-in request.
loopdb/sqlc/*	Updates SQL queries and models to include selected_amount.
loopd/swapclient_server.go	Updates quote requests and swap reporting to use the selected amount.
interface.go	Exposes a new SelectedAmount field in the loop-in request interface.
cmd/loop/staticaddr.go	Adds a new CLI flag and coin-selection logic for the swap amount.

Files not reviewed (4)

• loopdb/sqlc/migrations/000014_static_selected_amount.down.sql: Language not supported
• loopdb/sqlc/migrations/000014_static_selected_amount.up.sql: Language not supported
• loopdb/sqlc/queries/static_address_deposits.sql: Language not supported
• loopdb/sqlc/queries/static_address_loopin.sql: Language not supported

Comments suppressed due to low confidence (2)

staticaddr/deposit/interface.go:30

• [nitpick] Consider revising the comment for clarity. For example, change it to 'Returns all deposits associated with the given outpoints.'

// DepositsForOutpoints returns all deposits that behind the given

cmd/loop/staticaddr.go:639

• Review the dust limit check to ensure it correctly handles edge cases when the available deposit sum exactly equals the swap amount plus the dust limit. Clarifying the condition could prevent unexpected behavior in deposit selection.

if depositSum-int64(dustLimit) < amount {

[lightninglabs-deploy]

@starius: review reminder
@bhandras: review reminder
@sputn1ck: review reminder
@hieblmi, remember to re-request review from reviewers when ready

[hieblmi]

Rebased

[hieblmi]

Rebased

[hieblmi]

Rebased

[hieblmi]

Rebased

[hieblmi]

Rebased.