Chart builder: drop unparseable expressions mid-edit, polite glyphed inline feedback

docs/manual-verification.md

@@ -65,3 +65,15 @@
 
 - [ ] Library search / sort / empty states, the storage monitor, About & Donate
       modals, and the busy indicator all look deliberate and behave per spec.
+
+## Driving these checks headlessly
+
+The eye-checks above can be scripted as a headless walk-through (Playwright with the
+already-installed Chromium browser cache) for repeatable screenshots, alongside a live
+browser.
+
+- **Select by accessible name / role / placeholder, never by CSS class.** CSS-module class
+  names are content-hashed and unstable; the component tests select the same way.
+- **Reaching the Chart Builder:** open Datasets from the **header command button** (the
+  pane-toggle-strip `Datasets` button only exists once the workspace has content) → **New
+  Dataset** → paste rows inline → **Build Chart**.