Route base-branch lookups through the shared resolver

The four call sites that need a single base branch (legacy
behind-base loader, view-divergence menu, rebase-onto-base action,
move-commits-to-new-branch) now go through BaseBranchHelper.ResolveBaseBranch
in the GUI sites, and directly take candidates[0] in the loader. They
all use the same config-order tiebreak. No prompt yet — the helper
still returns the config-order first for ambiguous cases; subsequent
commits add the disambiguation menu.

MergeAndRebaseHelper and RefsHelper take BaseBranchHelper at
construction since helpers don't have access to Helpers() the way
controllers do.

pkg/gui/controllers.go

@@ -25,8 +25,9 @@ func (gui *Gui) resetHelpersAndControllers() {
 	helperCommon := gui.c
 	recordDirectoryHelper := helpers.NewRecordDirectoryHelper(helperCommon)
 	reposHelper := helpers.NewRecentReposHelper(helperCommon, recordDirectoryHelper, gui.onSwitchToNewRepo)
-	rebaseHelper := helpers.NewMergeAndRebaseHelper(helperCommon)
-	refsHelper := helpers.NewRefsHelper(helperCommon, rebaseHelper)
+	baseBranchHelper := helpers.NewBaseBranchHelper(helperCommon)
+	rebaseHelper := helpers.NewMergeAndRebaseHelper(helperCommon, baseBranchHelper)
+	refsHelper := helpers.NewRefsHelper(helperCommon, rebaseHelper, baseBranchHelper)
 	suggestionsHelper := helpers.NewSuggestionsHelper(helperCommon)
 	worktreeHelper := helpers.NewWorktreeHelper(helperCommon, reposHelper, refsHelper, suggestionsHelper)
 

pkg/gui/controllers/branches_controller.go

@@ -291,14 +291,10 @@ func (self *BranchesController) viewUpstreamOptions(selectedBranch *models.Branc
 	}
 
 	var disabledReason *types.DisabledReason
-	candidates, err := self.c.Git().Loaders.BranchLoader.GetBaseBranchCandidates(selectedBranch, self.c.Model().MainBranches)
+	baseBranch, _, _, err := self.c.Helpers().BaseBranch.ResolveBaseBranch(selectedBranch)
 	if err != nil {
 		return err
 	}
-	baseBranch := ""
-	if len(candidates) > 0 {
-		baseBranch = candidates[0]
-	}
 	if baseBranch == "" {
 		baseBranch = self.c.Tr.CouldNotDetermineBaseBranch
 		disabledReason = &types.DisabledReason{Text: self.c.Tr.CouldNotDetermineBaseBranch}

pkg/gui/controllers/helpers/merge_and_rebase_helper.go

@@ -19,6 +19,8 @@ import (
 type MergeAndRebaseHelper struct {
 	c *HelperCommon
 
+	baseBranchHelper *BaseBranchHelper
+
 	// Whether the "continue the rebase/merge?" prompt is currently on screen.
 	// We use this to auto-dismiss it if the operation stops being in the state
 	// that the prompt is offering to act on (e.g. it was continued or aborted
@@ -29,9 +31,11 @@ type MergeAndRebaseHelper struct {
 
 func NewMergeAndRebaseHelper(
 	c *HelperCommon,
+	baseBranchHelper *BaseBranchHelper,
 ) *MergeAndRebaseHelper {
 	return &MergeAndRebaseHelper{
-		c: c,
+		c:                c,
+		baseBranchHelper: baseBranchHelper,
 	}
 }
 
@@ -343,14 +347,10 @@ func (self *MergeAndRebaseHelper) RebaseOntoRef(ref string) error {
 		disabledReason = &types.DisabledReason{Text: self.c.Tr.CantRebaseOntoSelf}
 	}
 
-	candidates, err := self.c.Git().Loaders.BranchLoader.GetBaseBranchCandidates(checkedOutBranch, self.c.Model().MainBranches)
+	baseBranch, _, _, err := self.baseBranchHelper.ResolveBaseBranch(checkedOutBranch)
 	if err != nil {
 		return err
 	}
-	baseBranch := ""
-	if len(candidates) > 0 {
-		baseBranch = candidates[0]
-	}
 	if baseBranch == "" {
 		baseBranch = self.c.Tr.CouldNotDetermineBaseBranch
 		baseBranchDisabledReason = &types.DisabledReason{Text: self.c.Tr.CouldNotDetermineBaseBranch}

pkg/gui/controllers/helpers/refs_helper.go

@@ -18,16 +18,19 @@ import (
 type RefsHelper struct {
 	c *HelperCommon
 
-	rebaseHelper *MergeAndRebaseHelper
+	rebaseHelper     *MergeAndRebaseHelper
+	baseBranchHelper *BaseBranchHelper
 }
 
 func NewRefsHelper(
 	c *HelperCommon,
 	rebaseHelper *MergeAndRebaseHelper,
+	baseBranchHelper *BaseBranchHelper,
 ) *RefsHelper {
 	return &RefsHelper{
-		c:            c,
-		rebaseHelper: rebaseHelper,
+		c:                c,
+		rebaseHelper:     rebaseHelper,
+		baseBranchHelper: baseBranchHelper,
 	}
 }
 
@@ -428,14 +431,10 @@ func (self *RefsHelper) NewBranch(from string, fromFormattedName string, suggest
 
 func (self *RefsHelper) MoveCommitsToNewBranch() error {
 	currentBranch := self.c.Model().Branches[0]
-	candidates, err := self.c.Git().Loaders.BranchLoader.GetBaseBranchCandidates(currentBranch, self.c.Model().MainBranches)
+	baseBranchRef, _, _, err := self.baseBranchHelper.ResolveBaseBranch(currentBranch)
 	if err != nil {
 		return err
 	}
-	baseBranchRef := ""
-	if len(candidates) > 0 {
-		baseBranchRef = candidates[0]
-	}
 
 	withNewBranchNamePrompt := func(baseBranchName string, f func(string) error) error {
 		prompt := utils.ResolvePlaceholderString(