fix(ui): make the expander visible and the reply indent readable

Both were reported from the running application after the previous commit
claimed them working, and the tests that passed could not see either fault.

The expander took four attempts, each of which looked right in code:

  - QTreeView::drawBranches is the documented hook and does not work here. It
    runs BEFORE the row's cells, so with the expander on a content column the
    delegate's own background paints over it. A 60-pixel triangle survived as
    8, indistinguishable from the theme's near-invisible dot.
  - Sizing the glyph from the row rather than the branch rect put most of it
    outside that rect.
  - Moving it into SubjectDelegate but calling it from only the no-chip branch
    left every real row without one, since every real row has an account chip
    and takes the other branch.

It is now drawn by the delegate, which owns the cell and paints after the
background, from both branches, with setRootIsDecorated(false) so the style
does not draw its dot underneath.

The indent was 20px and invisible for a reason the geometry could not show: a
thread row draws an account chip before its subject and a reply row does not, so
a reply's text already starts about a chip's width LEFT of its thread's. The
indent has to beat that before any nesting reads at all, hence 72px.

The indent test asserted on visualRect, which was correctly indented the whole
time, and so passed against a build with no visible nesting. It now measures
where the TEXT lands, accounting for the chip, and fails at 20px. The new
expander test counts painted pixels of the glyph colour against a control row
with no replies, and fails when the call is dropped from either branch.

1 files changed, 18 insertions, 3 deletions

diff --git a/src/mainwindow.cpp b/src/mainwindow.cpp
index 720ec60..8bab2e8 100644
--- a/src/mainwindow.cpp
+++ b/src/mainwindow.cpp
@@ -559,9 +559,24 @@ void MainWindow::buildUi()
     // paperclip out of a 28px column entirely.
     m_threadView->setTreePosition(ThreadListModel::SubjectColumn);
 
-    // The root thread rows are the top level, so no decoration for them beyond
-    // the expander a thread with replies gets on its own.
-    m_threadView->setRootIsDecorated(true);
+    // No style-drawn branch decoration. SubjectDelegate draws the expander
+    // itself, because drawBranches runs BEFORE the row's cells and the
+    // delegate's own background paints straight over anything put there: a
+    // 60-pixel triangle survived as 8 pixels, indistinguishable from the
+    // near-invisible dot this replaces. Leaving both enabled would draw the
+    // theme's dot underneath the delegate's glyph.
+    m_threadView->setRootIsDecorated(false);
+
+    // Wider than Qt's default 20px, and the reason is specific rather than
+    // aesthetic. A thread row carries an account chip in front of its subject
+    // and a reply row does not, so a reply's text already starts roughly a
+    // chip's width (~60px) to the LEFT of its thread's. At the default indent
+    // the 20px shift is swallowed by that difference and the replies read as
+    // flush with the thread, or even outdented. Verified against the running
+    // app, not assumed: visualRect reported a correct 20px indent while the
+    // rendered text showed none, because the geometry is indented and the
+    // delegate then lays the text out from its own left edge.
+    m_threadView->setIndentation(SubjectDelegate::kReplyIndent);
 
     // Two delegates, and the split is not cosmetic. RowStyleDelegate carries
     // only the selection fix every column needs: the read/unread dimming