ui: draw the sidebar tabs without the placeholder icon

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/claude/invariants-gtk-and-chrome.md

@@ -252,7 +252,12 @@ Part of [CLAUDE.md](../../CLAUDE.md). These are rules that cost a defect to lear
   session file. An icon-only version existed (policy `narrow`, empty titles, the pills named in code by
   `name_side_tabs()`, because `narrow` still draws a label beside an icon); it was reversed because the
   glyphs were not understandable. A page added with an empty title is a blank pill, and
-  `switcher: … pills=N labels=N pages=N` reads it as `labels` below `pills`.
+  `switcher: … pills=N labels=N images=0 pages=N` reads it as `labels` below `pills`. **No icon at all**
+  is not what "no `icon-name`" gives you: `AdwViewSwitcherButton` always builds a `GtkImage` and falls
+  back to `image-missing` (the `[x]` placeholder, which also squeezed the title to "Meas..."), and no
+  property turns it off. `keep_tabs_icon_free()` (`src/ui_source.cpp`) hides every image in the switcher,
+  re-hides one that is shown again, and re-runs on the stack's `items-changed` (connected *after* the
+  switcher's own, so the new button exists) and on the switcher's `map`; `images=0` is the reading.
 - **An *overlaid* sidebar covers the plot, so a drag out of it has nowhere to land.** `collapsed` in an
   `AdwOverlaySplitView` means the sidebar sits *on* the plot rather than beside it: the pointer is over the
   list, never over a drop target, and a signal can be dragged but not dropped. `row_drag_sidebar()` hides