close §9: PanelSlot tested, the section is done

docs/workspace-panel-todo.md

@@ -1035,6 +1035,21 @@ they are marked below, because a dead-code list that is itself wrong is the wors
       try/catch was the whole difference, and the stub was deleted rather than left behind as a comment
       claiming credit for it.
 
+- [x] **`PanelSlot`, and with it this section.** _(`2c00c6a`, branch `agent-coordination-mvp`)_ — 25 tests
+      over the panel chrome, driving `PanelSlot` directly so the workspace can be put into states a whole
+      view cannot easily be pushed into: maximized, mid-swap, mobile. The substance is the mode matrix —
+      `interactive`, `locked`, `isMobile`, `isLastPanel`, `maximizedPanelId` and an app's own `zoomable`
+      /`transparent` flags combine in six separate ternaries spread over the file, and a control present
+      in a mode that should not have it is a way to edit a locked screen. Also pinned: the empty panel's
+      picker honours `availableOnPanel: false`; a screen-supplied `components` entry beats the registry
+      and its `header`/`provider`/`onClose` are all honoured; a throwing app is contained and offered a
+      clear only when the panel is the user's to edit; and the scale is CSS `zoom`, absent entirely at
+      100%, never `transform: scale`.
+      Nothing new found, and that is the honest result to record after two consecutive files where a test
+      found what review had not: the close button was the chrome's one defect and it was pinned by the
+      commit before this. **The Workspace directory is 112 tests across five files, green, and this
+      section is closed.**
+
 - [x] **A panel is told where it is, instead of being handed a key to reverse-engineer.** _(`dbe585f` +
       `717580f` + `585f234`, branch `agent-coordination-mvp`)_ — the first three items of §5.9. The
       context field `dashboardId: string` — which was never an id, always the whole `workspace.key` —