server: enable ExtraBudgetForInputs to be called before full server start up

This is a pure function that just returns what's basically a static
value. There's no risk of deadlock if a caller calls into this function
before the server has fully started up.

Author: Roasbeef

docs/release-notes/release-notes-0.7.0.md

@@ -36,6 +36,12 @@
   tombstone outputs on a full-value send (by using interactive transfers for V2
   addresses).
 
+- [Fixed a blocking startup issue where the server would hang during
+  initialization](https://github.com/lightninglabs/taproot-assets/pull/1780).
+  The `ExtraBudgetForInputs` function was refactored to be callable without
+  requiring a fully initialized AuxSweeper, allowing sweep operations to proceed
+  during server startup.
+
 # New Features
 
 ## Functional Enhancements

server.go

@@ -1262,11 +1262,7 @@ func (s *Server) ExtraBudgetForInputs(
 	srvrLog.Tracef("ExtraBudgetForInputs called, inputs=%v",
 		lnutils.SpewLogClosure(inputs))
 
-	if err := s.waitForReady(); err != nil {
-		return lfn.Err[btcutil.Amount](err)
-	}
-
-	return s.cfg.AuxSweeper.ExtraBudgetForInputs(inputs)
+	return tapchannel.ExtraBudgetForInputs(inputs)
 }
 
 // NotifyBroadcast is used to notify external callers of the broadcast of a

tapchannel/aux_sweeper.go

@@ -2557,9 +2557,7 @@ func (a *AuxSweeper) DeriveSweepAddr(inputs []input.Input,
 
 // ExtraBudgetForInputs takes a set of inputs and maybe returns an extra budget
 // that should be added to the sweep transaction.
-func (a *AuxSweeper) ExtraBudgetForInputs(
-	inputs []input.Input) lfn.Result[btcutil.Amount] {
-
+func ExtraBudgetForInputs(inputs []input.Input) lfn.Result[btcutil.Amount] {
 	inputsWithBlobs := fn.Filter(inputs, func(i input.Input) bool {
 		return i.ResolutionBlob().IsSome()
 	})
@@ -2581,6 +2579,14 @@ func (a *AuxSweeper) ExtraBudgetForInputs(
 	return lfn.Ok(extraBudget)
 }
 
+// ExtraBudgetForInputs takes a set of inputs and maybe returns an extra budget
+// that should be added to the sweep transaction.
+func (a *AuxSweeper) ExtraBudgetForInputs(
+	inputs []input.Input) lfn.Result[btcutil.Amount] {
+
+	return ExtraBudgetForInputs(inputs)
+}
+
 // NotifyBroadcast is used to notify external callers of the broadcast of a
 // sweep transaction, generated by the passed BumpRequest.
 func (a *AuxSweeper) NotifyBroadcast(req *sweep.BumpRequest,