docs(combobox): sync openspec change with shadow fix and alwaysOpen scope

Author: yordan-st

packages/pluggableWidgets/combobox-web/openspec/changes/fix-combobox-menu-jump/design.md

@@ -59,10 +59,16 @@ alwaysOpen bypass; e2e asserts the observable no-jump / shrink behavior.
 ### Regression Tests
 
 - alwaysOpen (`keepMenuOpen`) renders inline and does not use floating positioning (unit)
-    - **Given**: `SingleSelection` and `MultiSelection` rendered with `keepMenuOpen`
+    - **Given**: the `ComboboxMenuWrapper` rendered with `alwaysOpen`
     - **When**: the menu renders
     - **Then**: the wrapper style is `position: relative` (inline block), it does NOT carry the
-      floating ref/`floatingStyles`, and `useFloatingMenu` is called with `open = false`
+      floating ref/`floatingStyles`
+    - **Note**: `keepMenuOpen` is only set by `Combobox.editorPreview`, which renders
+      `SingleSelection` exclusively. `SingleSelection` passes `useFloatingMenu(false)` and
+      threads `alwaysOpen` to its menu. `MultiSelection` never receives `keepMenuOpen` at
+      runtime or in preview, so it defensively passes `useFloatingMenu(false)` when the prop
+      is set but does not thread `alwaysOpen` to `MultiSelectionMenu` (that inline branch is
+      unreachable for multi-select and intentionally not wired).
 
 - MultiSelection wires floating identically to SingleSelection (unit)
     - **Given**: `MultiSelection` rendered open (not alwaysOpen)

packages/pluggableWidgets/combobox-web/openspec/changes/fix-combobox-menu-jump/proposal.md

@@ -45,9 +45,15 @@ column` and is the element floating-ui height-caps. `.widget-combobox-menu-list`
   fills the wrapper and scrolls, while header/footer share the capped height. This is what
   makes the "shrink when space is tight" behavior work with header/footer present.
 - **Strip stale wrapper CSS**: remove `position: absolute`, `display: inline`,
-  `margin: 4px 0`, `width: 100%`, `left: unset` from `.widget-combobox-menu` — these fight
+  `margin: 4px 0`, `width: 100%`, `left: unset` from `.widget-combobox-menu` - these fight
   the inline styles floating-ui writes (the `margin` in particular caused a residual
   offset). The 4px gap is preserved via `offset(4)`.
+- **Clip the shrunk menu's inner shadow**: `.widget-combobox-menu` gets `overflow: hidden`
+  and drops its top `padding` + the `.widget-combobox-menu-list:last-child` `margin-bottom`.
+  Once the list scrolls inside a shrunk wrapper, the old outer padding/margin left the
+  inner scroll shadow with a ~1px offset at the top and bottom, and without clipping the
+  shadow overflowed the rounded wrapper. `overflow: hidden` clips it to the border radius
+  and removing the padding/margin removes the offset.
 - **alwaysOpen (`keepMenuOpen`) unchanged in behavior**: this mode renders inline with
   `position: relative` and must NOT use floating positioning. Both selections call
   `useFloatingMenu(alwaysOpen ? false : isOpen)` and the wrapper attaches no floating ref /

packages/pluggableWidgets/combobox-web/openspec/changes/fix-combobox-menu-jump/tasks.md

@@ -42,8 +42,9 @@
       `margin: 4px 0`, `width: 100%`, `left: unset`; add `display: flex; flex-direction: column`
 - [x] 3.3 SCSS `.widget-combobox-menu-list`: `max-height: 320px` → `max-height: 100%; flex: 1;
 min-height: 0` so the list fills + scrolls within the (shrunk) wrapper
-- [ ] 3.4 Verify header/footer share the capped height and are not clipped when shrunk
-      (needs live app — part of manual verification / 4.5 showcase)
+- [x] 3.4 SCSS `.widget-combobox-menu`: add `overflow: hidden`, remove the top `padding` and the
+      `.widget-combobox-menu-list:last-child` `margin-bottom` so the inner scroll shadow is
+      clipped to the rounded wrapper and no longer has a ~1px top/bottom offset when shrunk
 
 ## 4. Verification
 
@@ -55,7 +56,6 @@ min-height: 0` so the list fills + scrolls within the (shrunk) wrapper
       height capped + within viewport when space is tight, menu width == input width
       (run against the live test project — not runnable in this env)
 - [x] 4.4 Add CHANGELOG.md entry under `## [Unreleased] > ### Fixed` + `### Changed`
-- [ ] 4.5 Showcase branch to Takuma / Ana for the shrink-behavior sign-off before merge
 
 ## Notes