From 50a55d9045fd072b4172b4d7c8a56891dc889ddf Mon Sep 17 00:00:00 2001
From: Sergio Esteban <sergio.esteban.ce@gmail.com>
Date: Fri, 15 May 2026 12:16:41 +0200
Subject: [PATCH] fix(ui): prevent LazyVStack layout hang with 700+ cards
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The sidebar ListBoardView used LazyVStack with pinnedViews:
[.sectionHeaders], but each section wrapped its cards in an inner
LazyVStack. The outer container needed to measure each section to
position pinned headers, which required materializing the inner
LazyVStack — forcing all ~700 card views to be laid out on every
reconciliation cycle. Thread samples confirmed 100% main thread time
spent in LazySubviewPlacements.placeSubviews → ForEachList.applyNodes.

Two changes:
- Remove pinnedViews from the outer LazyVStack so sections are lazily
  evaluated without full measurement
- Replace the inner LazyVStack with VStack so the outer container can
  size sections via their direct children

Also move ChannelShareController drain loops from Task.detached to
DispatchQueue.global to avoid blocking the cooperative thread pool
with synchronous FileHandle.availableData reads.
---
 Sources/KanbanCode/ChannelShareController.swift | 5 ++---
 Sources/KanbanCode/ListBoardView.swift          | 4 ++--
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/Sources/KanbanCode/ChannelShareController.swift b/Sources/KanbanCode/ChannelShareController.swift
index 1d9faf4..7564b0d 100644
--- a/Sources/KanbanCode/ChannelShareController.swift
+++ b/Sources/KanbanCode/ChannelShareController.swift
@@ -230,12 +230,11 @@ final class ChannelShareController {
     }
 
     private static func drainStderr(_ handle: FileHandle, tag: String) {
-        Task.detached {
+        DispatchQueue.global(qos: .utility).async {
             while true {
                 let data = handle.availableData
                 if data.isEmpty { return }
                 if let s = String(data: data, encoding: .utf8) {
-                    // Keep share-related diagnostics quiet unless debugging.
                     FileHandle.standardError.write(Data("\(tag) \(s)".utf8))
                 }
             }
@@ -243,7 +242,7 @@ final class ChannelShareController {
     }
 
     private static func drainStdout(_ handle: FileHandle, tag: String) {
-        Task.detached {
+        DispatchQueue.global(qos: .utility).async {
             while true {
                 let data = handle.availableData
                 if data.isEmpty { return }
diff --git a/Sources/KanbanCode/ListBoardView.swift b/Sources/KanbanCode/ListBoardView.swift
index a2ded9e..f16b235 100644
--- a/Sources/KanbanCode/ListBoardView.swift
+++ b/Sources/KanbanCode/ListBoardView.swift
@@ -61,7 +61,7 @@ struct ListBoardView: View {
 
     private func scrollView(proxy: ScrollViewProxy) -> some View {
         ScrollView {
-            LazyVStack(alignment: .leading, spacing: 0, pinnedViews: [.sectionHeaders]) {
+            LazyVStack(alignment: .leading, spacing: 0) {
                 channelsSection
                 ForEach(sections, id: \.column) { section in
                     sectionView(for: section)
@@ -350,7 +350,7 @@ private struct ListBoardSectionView: View {
                 onReorderCard: onReorderCard
             ))
         } else {
-            LazyVStack(spacing: 4) {
+            VStack(spacing: 4) {
                 ForEach(section.cards) { card in
                     if dragState.reorderTargetId == card.id && dragState.reorderAbove {
                         ReorderIndicator()