help: the search block's (i) on its header, a 12 px mark, and a real search page

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

@@ -544,26 +544,34 @@ The `Help` submenu, the contextual help's "?" and the guided tour, and the traps
   sits *on* whatever is under it -- and every panel heading already has a switch or a pencil in a
   corner. `src/ui_context_help.cpp` is a table of (id, title, body, shortcut, host) where the host is
   the *row* -- a panel's heading usually, and the row of a specific control (the "record events"
-  switch, the pre-trigger share) where that is the thing being explained. The one exception is the
+  switch, the pre-trigger share, the search block's expander *header*) where that is the thing being
+  explained. The one exception is the
   plot, which has no heading: its "(i)" is an overlay child of the overlay the layout editor already
   uses, and its corner is free. The icon is **`dialog-information-symbolic`** -- `help-about-symbolic`
   is *already* the status bar's information button, and two "help" glyphs meaning different things on
   the same line is the trap the seven app icons exist to avoid; the dump reads the name back through
   the theme for the same reason the pane [edit] buttons do. `math_head` exists only while the math
   editor is open, so that row is skipped when it is null.
-- **A `GtkMenuButton` ignores both `min-width` and a size request; its subnodes are where a small
-  one is made.** The "(i)" is meant to be a *mark*, not a button, and the default is 34x34 (a 24 px
-  floor plus 5 px of padding from Adwaita's `button` rule). Measured on libadwaita 1.10: setting
+- **A `GtkMenuButton` ignores both `min-width` and a size request, and the icon is a node *below*
+  its `button` subnode.** The "(i)" is meant to be a *mark*, not a button, and the default is 34x34 (a
+  24 px floor plus 5 px of padding from Adwaita's `button` rule). Measured on libadwaita 1.10: setting
   `min-width`/`min-height` on the widget changed nothing, and neither did `gtk_widget_set_size_request()`
-  -- the menu button's own measure wins. Three selectors are needed, all in `install_css()`:
-  `menubutton.udpscope-hint` (the outer node), `menubutton.udpscope-hint > button` (its subnode) and
-  `... > button > image` (the glyph), with `min-width: 0; min-height: 0; padding: 0` -- and the result
-  is **16x16**, the glyph's own size, because a `min-width` is a floor and not a cap. (A class on the
-  outer node alone leaves the subnode at 34; a class on the subnode alone shrank the width to 16 and
-  left the height at 26.) The dump's `hint=` reading is that number, and it is measured with
-  `gtk_widget_compute_bounds()` on the first *visible* hint -- a hint inside a collapsed `GtkExpander`
-  is not in the widget-parent chain at all and reads 0x0, which would look like a mark shrunk to
-  nothing.
+  -- the menu button's own measure wins. The node tree is `menubutton > button > box > image` (read off
+  the CSS node dump), so `install_css()` reaches the glyph as
+  `menubutton.udpscope-hint > button > box > image`. The direct-grandchild form `> button > image`
+  matches **nothing** and is silent about it -- the glyph keeps its natural 16 px, which is why an
+  earlier version shipped a 16x16 mark and took that for the floor it was not. Zeroing the outer node
+  and the `button` subnode and asking the glyph for **12 px** (`min-width`/`min-height` *and*
+  `-gtk-icon-size`, the latter what actually *scales* the drawing rather than clamping its box) gives
+  **12x12**. (A class on the outer node alone leaves the subnode at 34; a class on the subnode alone
+  shrank the width to 16 and left the height at 26.) There is no lower floor: the symbolic glyph renders
+  at any request (measured down to 4 px), so 12 px is a legibility choice and not a limit. The dump's
+  `hint=` reading is that number, measured with `gtk_widget_compute_bounds()` on the first *visible*
+  hint -- a hint inside a collapsed `GtkExpander`'s *child* is not in the widget-parent chain at all and
+  reads 0x0, which would look like a mark shrunk to nothing. That is why the search block's hint rides
+  the expander's **header** (a `label-widget` box, `search_head` in `src/ui/trigger-panel.ui`, which
+  *is* in the tree) rather than its child, and why the `[helpui] collapsed search:` reading asserts the
+  header hint is mapped and 12x12 while the block is collapsed.
 - **Off is gone, not greyed, and the buttons are found by a data key rather than kept in a list.** The
   list is what the math editor cannot survive: its heading lives in a builder that is dropped and
   rebuilt on every opening, so a stored pointer into it would go stale one dialog later. A key on the