Optimize view/modify TUI load time with parallel fetching

- Deduplicate API calls: syncStackPRs now returns PRDetails for
  LoadBranchNodes to reuse, eliminating redundant FindPRDetailsForBranch calls
- Parallelize API calls in syncStackPRs (capped at 6 concurrent requests)
- Parallelize git operations in LoadBranchNodes (capped at 4 concurrent)
- Show "Loading stack..." indicator for interactive sessions

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: skarim

cmd/init.go

@@ -320,7 +320,7 @@ func runInit(cfg *config.Config, opts *initOptions) error {
 			}
 		}
 	} else {
-		syncStackPRs(cfg, latestStack)
+		_ = syncStackPRs(cfg, latestStack)
 	}
 
 	if err := stack.Save(gitDir, sf); err != nil {

cmd/merge.go

@@ -41,7 +41,7 @@ func runMerge(cfg *config.Config, target string) error {
 	currentBranch := result.CurrentBranch
 
 	// Sync PR state from GitHub so merge status is up to date.
-	syncStackPRs(cfg, s)
+	_ = syncStackPRs(cfg, s)
 
 	// Persist the refreshed PR state.
 	stack.SaveNonBlocking(result.GitDir, result.StackFile)

cmd/modify.go

@@ -64,7 +64,7 @@ func runModify(cfg *config.Config) error {
 	currentBranch := result.CurrentBranch
 
 	// Load branch data for the TUI
-	viewNodes := stackview.LoadBranchNodes(cfg, s, currentBranch)
+	viewNodes := stackview.LoadBranchNodes(cfg, s, currentBranch, result.PRDetails)
 
 	// Reverse so index 0 = top of stack (matching visual order)
 	reversed := make([]stackview.BranchNode, len(viewNodes))
@@ -283,8 +283,15 @@ func checkModifyPreconditions(cfg *config.Config) (*loadStackResult, error) {
 		return nil, ErrSilent
 	}
 
+	// Show loading indicator while syncing PRs
+	fmt.Fprintf(cfg.Err, "Loading stack...")
+
 	// Sync PR state and check merge queue
-	syncStackPRs(cfg, s)
+	prDetails := syncStackPRs(cfg, s)
+	result.PRDetails = prDetails
+
+	fmt.Fprintf(cfg.Err, "\r\033[2K")
+
 	if err := modify.CheckNoMergeQueuePRs(cfg, s); err != nil {
 		return nil, ErrSilent
 	}

cmd/push.go

@@ -78,7 +78,7 @@ func runPush(cfg *config.Config, opts *pushOptions) error {
 		return ErrSilent
 	}
 	// Sync PR state to detect merged/queued PRs before pushing.
-	syncStackPRs(cfg, s)
+	_ = syncStackPRs(cfg, s)
 
 	merged := s.MergedBranches()
 	if len(merged) > 0 {

cmd/rebase.go

@@ -176,7 +176,7 @@ func runRebase(cfg *config.Config, opts *rebaseOptions) error {
 		branchesToRebase[0].Branch, branchesToRebase[len(branchesToRebase)-1].Branch)
 
 	// Sync PR state before rebase so we can detect merged PRs.
-	syncStackPRs(cfg, s)
+	_ = syncStackPRs(cfg, s)
 
 	branchNames := make([]string, 0, len(s.Branches))
 	for _, b := range s.Branches {
@@ -349,7 +349,7 @@ func runRebase(cfg *config.Config, opts *rebaseOptions) error {
 
 	updateBaseSHAs(s)
 
-	syncStackPRs(cfg, s)
+	_ = syncStackPRs(cfg, s)
 
 	stack.SaveNonBlocking(gitDir, sf)
 
@@ -540,7 +540,7 @@ func continueRebase(cfg *config.Config, gitDir string) error {
 
 	updateBaseSHAs(s)
 
-	syncStackPRs(cfg, s)
+	_ = syncStackPRs(cfg, s)
 
 	stack.SaveNonBlocking(gitDir, sf)
 

cmd/submit.go

@@ -108,7 +108,7 @@ func runSubmit(cfg *config.Config, opts *submitOptions) error {
 	}
 
 	// Sync PR state to detect merged/queued PRs before pushing.
-	syncStackPRs(cfg, s)
+	_ = syncStackPRs(cfg, s)
 
 	// Resolve remote for pushing
 	remote, err := pickRemote(cfg, currentBranch, opts.remote)
@@ -189,7 +189,7 @@ func runSubmit(cfg *config.Config, opts *submitOptions) error {
 
 	// Update base commit hashes and sync PR state
 	updateBaseSHAs(s)
-	syncStackPRs(cfg, s)
+	_ = syncStackPRs(cfg, s)
 
 	if err := stack.Save(gitDir, sf); err != nil {
 		return handleSaveError(cfg, err)

cmd/sync.go

@@ -134,7 +134,7 @@ func runSync(cfg *config.Config, opts *syncOptions) error {
 		cfg.Printf("Rebasing stack ...")
 
 		// Sync PR state to detect merged PRs before rebasing.
-		syncStackPRs(cfg, s)
+		_ = syncStackPRs(cfg, s)
 
 		// Save original refs so we can restore on conflict.
 		// Merged branches that no longer exist locally have no ref to
@@ -311,7 +311,7 @@ func runSync(cfg *config.Config, opts *syncOptions) error {
 	// --- Step 5: Sync PR state ---
 	cfg.Printf("")
 	cfg.Printf("Syncing PRs ...")
-	syncStackPRs(cfg, s)
+	_ = syncStackPRs(cfg, s)
 
 	// Report PR status for each branch
 	for _, b := range s.Branches {