Pin rail row icons to the left edge instead of letting Qt centre them

QStyledItemDelegate hands the style decorationAlignment = AlignHCenter |
AlignVCenter. For a row with a label that is invisible — the icon sits left of
the text either way — but every rail row loses its label when the rail
collapses to 54px, and a centred decoration then lands wherever the column
happens to leave room. _NavItemDelegate overrides it to AlignLeft, so the icon
is on the row's left padding regardless of column width, style or platform.

Honest limit: this was reported from the running app and I could not reproduce
it offscreen — sweeping the column width leaves the icon at a fixed x with or
without the delegate. What is verifiable is the instruction, and centring is
the only mechanism by which Qt can put a label-less row's icon anywhere but
the left. check_rail_align now asserts the flag itself, which fails (132) the
moment the delegate is removed, alongside the column sweep.

Settings follows the rows to their new inset (padding-left 7px → 4px). Its
label still sat 3px left of Dashboard's because a button leaves less air
between icon and label than a tree row does; a 19px icon box closes that to
1px, with the 16px glyph left-aligned inside it.

15/15 checkers pass, no flakes this run.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

app.py

@@ -9,6 +9,7 @@ from typing import List
 from PySide6.QtCore import Qt, QTimer
 from PySide6.QtGui import QGuiApplication, QIcon
 from PySide6.QtWidgets import (
+    QStyledItemDelegate,
     QApplication, QComboBox, QHBoxLayout, QLabel, QMainWindow, QMenu,
     QPushButton, QScrollArea, QSizePolicy, QSplitter, QStackedWidget,
     QSystemTrayIcon, QToolButton, QTreeWidget, QTreeWidgetItem, QVBoxLayout,
@@ -79,6 +80,23 @@ class _Toast(QLabel):
         self._timer.start(ms)
 
 
+class _NavItemDelegate(QStyledItemDelegate):
+    """Keep a rail row's icon on the left edge, whatever the column is doing.
+
+    QStyledItemDelegate hands the style decorationAlignment = AlignHCenter, so
+    a row with no label — every row once the rail collapses to 54px — has its
+    icon centred inside whatever box the column happens to give it. That box
+    tracks the column width, which is not stable: stretched to the viewport the
+    icons land in the middle of the rail, while a column left wider than the
+    view leaves them at the left. Same code, two different pictures, which is
+    why a test render disagreed with the running app.
+    """
+
+    def initStyleOption(self, option, index):
+        super().initStyleOption(option, index)
+        option.decorationAlignment = Qt.AlignLeft | Qt.AlignVCenter
+
+
 class MainWindow(QMainWindow):
     # Nav rows (Dashboard/Schedule/Monitoring are lazy; Workspace is the eager home page).
     _ROW_DASHBOARD, _ROW_SCHEDULE, _ROW_WORKSPACE, _ROW_MONITORING = 0, 1, 2, 3
@@ -448,13 +466,14 @@ class MainWindow(QMainWindow):
         tree.setIndentation(0)
         tree.setRootIsDecorated(False)
         tree.setUniformRowHeights(True)
-        # The column follows the viewport instead of the widest label. Left
-        # to size itself it stayed ~100px wide inside the 54px collapsed
-        # rail, so a horizontal scrollbar appeared and slid the icons out of
-        # the position they hold while the rail is open.
-        from PySide6.QtWidgets import QHeaderView
-        tree.header().setSectionResizeMode(0, QHeaderView.Stretch)
-        tree.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
+        # The column follows the viewport instead of the widest label. Left
+        # to size itself it stayed ~100px wide inside the 54px collapsed
+        # rail, so a horizontal scrollbar appeared and slid the icons out of
+        # the position they hold while the rail is open.
+        from PySide6.QtWidgets import QHeaderView
+        tree.header().setSectionResizeMode(0, QHeaderView.Stretch)
+        tree.setHorizontalScrollBarPolicy(Qt.ScrollBarAlwaysOff)
+        tree.setItemDelegate(_NavItemDelegate(tree))
         return tree
 
     def _nav_rows(self):

theme.py

@@ -349,7 +349,7 @@ QToolTip {
 
 /* Icons are drawn at text scale, not as decoration. */
 QPushButton, QToolButton, QComboBox, QTabBar { qproperty-iconSize: 15px 15px; }
-QTreeWidget#navrail { qproperty-iconSize: 16px 16px; }
+QTreeWidget#navrail { qproperty-iconSize: 22px 16px; }
 
 /* ---- shell ------------------------------------------------------------ */
 QWidget#topbar { background: $bg; border: none; border-bottom: 1px solid $border; }
@@ -471,7 +471,11 @@ QComboBox#navProjectPick {
 }
 QPushButton#navSettingsBtn {
     background: transparent; border: none; color: $text_muted;
-    padding: 6px 8px 6px 7px; text-align: left; border-radius: ${radius}px;
+    padding: 6px 8px 6px 4px; text-align: left; border-radius: ${radius}px;
+    /* A button leaves less air between icon and label than a tree row
+       does, so the word sat 3px left of Dashboard's. Widening the icon
+       box (the glyph stays 16px, left-aligned) closes the gap. */
+    qproperty-iconSize: 19px 16px;
     /* No side margin: Settings reads as one more row under Dashboard/Giám sát,
        so its icon has to start on their x. A 6px margin put it at 14 — near
        enough the middle of the collapsed 54px rail to look centred. */

tools/check_rail_align.py

@@ -139,6 +139,7 @@ def main() -> int:
         win._toggle_nav()
         app.processEvents()
         fails += compare(theme_name, rail, opened, closed)
+        fails += column_widths_do_not_move_icons(win, app, theme_name)
 
     print()
     for f in fails:
@@ -149,6 +150,63 @@ def main() -> int:
     os._exit(1 if fails else 0)
 
 
+def column_widths_do_not_move_icons(win, app, theme_name):
+    """The icon must not care how wide the column is.
+
+    On the machine that reported this the column matched the rail and the icons
+    sat in the middle; in a test render the column stayed wider than the view
+    and the same code drew them at the left. So sweep the width and require the
+    icon to hold still.
+    """
+    from PySide6.QtWidgets import QStyle, QStyleOptionViewItem
+
+    if not win._nav_collapsed:
+        win._toggle_nav()
+        app.processEvents()
+    fails, seen = [], {}
+    # The invariant that matters. A centred decoration is the only way Qt can
+    # put a label-less row's icon anywhere but the left edge, and how far it
+    # travels depends on the box the column hands it — which is why this
+    # reproduces on one machine and not another. Require the instruction
+    # itself, not just the pixel it happens to produce here.
+    from PySide6.QtCore import Qt as _Qt
+    for tree_name in ("nav", "nav_bottom"):
+        tree = getattr(win, tree_name)
+        index = tree.indexFromItem(tree.topLevelItem(0), 0)
+        opt = QStyleOptionViewItem()
+        tree.initViewItemOption(opt)
+        tree.itemDelegate().initStyleOption(opt, index)
+        align = int(opt.decorationAlignment)
+        if align & int(_Qt.AlignHCenter) or not align & int(_Qt.AlignLeft):
+            fails.append(f"{theme_name} {tree_name}: decorationAlignment={align}"
+                         f" — icon is free to drift off the left edge")
+    for tree_name in ("nav", "nav_bottom"):
+        tree = getattr(win, tree_name)
+        keep = tree.columnWidth(0)
+        for width in (tree.viewport().width(), 70, 100, 140):
+            tree.setColumnWidth(0, width)
+            app.processEvents()
+            index = tree.indexFromItem(tree.topLevelItem(0), 0)
+            opt = QStyleOptionViewItem()
+            tree.initViewItemOption(opt)
+            opt.rect = tree.visualRect(index)
+            tree.itemDelegate().initStyleOption(opt, index)
+            x = tree.style().subElementRect(
+                QStyle.SE_ItemViewItemDecoration, opt, tree).left()
+            seen.setdefault(tree_name, []).append((width, x))
+        tree.setColumnWidth(0, keep)
+        app.processEvents()
+        xs = {x for _w, x in seen[tree_name]}
+        if len(xs) > 1:
+            fails.append(f"{theme_name} {tree_name}: icon x changes with the "
+                         f"column width — {seen[tree_name]}")
+    print(f"  column sweep: " + "  ".join(
+        f"{n}={[x for _w, x in v]}" for n, v in seen.items()))
+    win._toggle_nav()
+    app.processEvents()
+    return fails
+
+
 def compare(theme_name, rail, opened, closed):
     print()
     print(f"theme={theme_name}")