Chart Builder: open a snippet in the builder to edit it in place

docs/IMPLEMENTATION-PLAN.md

@@ -515,11 +515,17 @@ is in the maintained plan, not the archive.
 
 **Chart Builder** (`exploration/chart-builder-enhancement-scope.md`):
 
-- **Open-in-builder + builder starter examples (3B/3C)** — the next builder slice in the
-  scope doc: hydrate the **builder** from an existing spec (strict spec→config parse), behind
-  a starter-example front door. Distinct from the shipped onboarding gallery
-  (`core/examples.ts` → `Onboarding.tsx`), which seeds a snippet straight into the editor, not
-  the builder — there is no spec→builder-config path yet.
+- ~~**Open-in-builder (3C, strict hydration)**~~ ✅ shipped (2026-06-18): an editor-toolbar
+  **Open in builder** action reopens a builder-representable snippet to **edit it in place**
+  (`parseChartSpec` is the strict inverse of `buildChartSpec`, gated by re-assemble +
+  deep-compare). Only dataset-referencing specs hydrate (the builder's data model). See the
+  scope doc status log.
+- **Builder starter examples (3B)** — a small set of curated starters, one per covered FT
+  intent, **authored in the builder dialect so they reopen via 3C**. Reshaped by 3C's
+  data-model edge: a builder-openable starter must reference a dataset, so 3B ships paired
+  sample datasets (or is reframed) — decide its shape now that the gate is live. Distinct from
+  the shipped onboarding gallery (`core/examples.ts` → `Onboarding.tsx`), which seeds an
+  inline-data snippet straight into the editor (Monaco-only, never the builder).
 - ~~**Transform-aware data inspector** — show resolved post-transform rows~~ ✅ shipped: an
   Input | Resolved data inspector below the Live Preview and Chart Builder charts, with a
   draggable height divider (spec §04; arch 05 → "data inspector rides the boundary").