staticaddr: channel funding with deposits

[hieblmi]

This PR introduces a openchannel subcommand to static addresses.

It provides the same experience as lncli openchannel.
Exmples:

Open a channel with all available deposits:

loop static openchannel --fundmax --sat_per_vbyte XXX --private ...

Open a channel with specified local funding amount, coin-selected from available deposits under fee and dust considerations.

loop static openchannel --local_amt XXX --sat_per_vbyte YYY --private ...

Open a channel from two deposits AAA and BBB while taking their combined value(fundmax) as funding amount and considering fees and dust limit.

loop static openchannel --utxo AAA --utxo BBB --fundmax --sat_per_vbyte YYY --private ...

Open a channel from two deposits AAA and BBB while taking a specified amount(local_amt) as funding amount and considering fees and dust limit.

loop static openchannel --utxo AAA --utxo BBB --local_amt --sat_per_vbyte YYY --private ...

TODOs:

• Integration tests

[gemini-code-assist]

Summary of Changes

Hello @hieblmi, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly extends the functionality of static addresses by enabling them to be used as a source for funding Lightning channels. It introduces a new openchannel command that integrates a robust PSBT-based funding flow with lnd, offering flexible options for selecting deposits. This enhancement allows users to seamlessly convert their static address funds into channel liquidity, thereby increasing the utility and versatility of static addresses within the Lightning ecosystem.

Highlights

• New openchannel subcommand: Introduced a new openchannel subcommand under loop static which allows users to fund Lightning channels directly from their static address deposits.
• Flexible Channel Funding Options: The new command supports various funding options, including fundmax to use all available deposits, local_amt for a specified amount, and explicit UTXO selection, mirroring the experience of lncli openchannel.
• PSBT-based Funding Flow: The channel funding process leverages a Partially Signed Bitcoin Transaction (PSBT) flow, enabling secure and collaborative transaction construction with lnd.
• New Deposit States: Added new deposit states, opening_channel and channel_published, to track the lifecycle of deposits used for channel funding.
• Code Refactoring and Reusability: Common utility functions related to PSBTs, Musig2 sessions, and outpoint handling have been refactored into a new staticutil package, improving code organization and reusability across static address features.

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[gemini-code-assist]

Code Review

This pull request introduces a new openchannel subcommand for static addresses, allowing users to fund channels from their deposits. The implementation is comprehensive, covering the command-line interface, RPC definitions, daemon logic, and documentation.

My review focuses on the new cmd/loop/openchannel.go file, where I've identified a few issues related to context handling, input validation, and error wrapping. These are important for ensuring the robustness and maintainability of the new command.

The refactoring to move utility functions into a staticutil package is a great improvement for code organization and reuse. The protocol changes to use PSBT for withdrawals are also a solid enhancement.

Overall, this is a well-structured PR that adds significant functionality. Addressing the feedback will further improve its quality.

[hieblmi]

@gemini-code-assist review

[sputn1ck]

Review notes (short):

• Any error after PSBT finalize currently transitions deposits back to Deposited. If finalize already handed tx to lnd (NoPublish=false), we can end up reusing spent deposits. Can we gate rollback once finalize is sent or persist txid/reconcile?
• On recover, OpeningChannel just self-loops with no action. If we restart mid-flow, deposits can remain locked forever. Should we reconcile against lnd pending channels or on-chain spends?
• We estimate fee twice when sat_per_vbyte is unset (calc vs PSBT build). Funding amount can be computed with one rate and PSBT built with another. Can we thread a single fee rate through?
• MinConfs is effectively ignored (hard-coded to 1), but checkPsbtFlags only checks !=1/SpendUnconfirmed. Should we validate and reject unsupported MinConfs explicitly before locking deposits?
• SelectDeposits doesn’t account for fees. We lock deposits based only on local_amt + dust, then may fail when fee is applied. Worth a fee-aware selection or pre-check before OnOpeningChannel.

[sputn1ck]

Inline notes.

[lightninglabs-deploy]

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

[hieblmi]

Hi @sputn1ck, I addressed some more findings, namely:

• Added crash recovery for OpeningChannel deposits.
• Upgraded permissions to swap:execute for both StaticOpenChannel and StaticAddressLoopIn.
• Aligned channel-open fee/value calculation paths by threading commitment type into tx construction.
• Hardcoded forwarded SpendUnconfirmed to false.
• Added unit tests for openchannel recovery logic.