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):