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

docs/exploration/chart-builder-enhancement-scope.md

@@ -25,6 +25,32 @@
 Newest first. The at-a-glance build-order tracker is §4; per-item detail is §3. This log is
 the quick "where are we" — read it first.
 
+- **2026-06-18 (3C open-in-builder, edit-in-place)** — **the builder became create-and-revise.**
+  Core: `parseChartSpec` / `parseChartSpecText` (`chart-builder.ts`) — the strict inverse of
+  `buildChartSpec`, gated by **re-assemble + canonical deep-compare** (ignoring key order,
+  `$schema`, the injected `mark.tooltip`), so the gate widens for free as the dialect grows and
+  never lets the builder overwrite a richer spec. `unescapeVegaField` added beside its escape
+  twin (`rendering.ts`). Save semantics chosen with the user = **edit in place** (not
+  always-create): `SnippetStore.replaceSnippetSpec` republishes the built spec into both the
+  snippet's versions (auto names re-derive like publish; user names kept), and
+  `ChartBuilderStore` gained `editingSnippetId`/`editingSnippetName` + `openForEdit`/`saveEdits`.
+  Entry point: an **editor-toolbar** _Open in builder_ action (`SpecEditor`), beside _Extract to
+  Dataset_, shown only when the published spec round-trips _and_ its dataset exists — **hidden
+  otherwise** (content-gated, like Extract). The modal's primary becomes **Save changes** with an
+  "Editing _name_" banner; a dedicated `openChartBuilderForEdit` coordinator opener hydrates
+  before showing the modal so the registry's default `init` can't clobber it. **Data-model edge
+  (called out, not a bug):** the builder references a dataset by name, so only dataset-referencing
+  specs hydrate — inline-data snippets (incl. the onboarding gallery) stay Monaco-only. This
+  reshapes **3B**: builder-openable starters need a paired dataset, so 3B's shape is decided
+  _after_ this lands (see §3). Spec §06 gained an _Open in builder_ section. **Placement settled
+  by council:** an initial library metadata-panel placement (beside Duplicate/Delete) tested
+  undiscoverable; `/council` (NN/g #6 recognition / #4 consistency; Carbon button usage) put it in
+  the editor toolbar and settled the hidden-vs-disabled question via the toolbar's own precedent —
+  **content-gated** actions hide (Extract, Open-in-builder), **state-gated** ones disable (Revert,
+  Config). Recorded as a contract rule in `architecture/10` §5; the parked `ux-second-pass.md` row
+  is closed. Verified: typecheck + full tests (1089) + eslint + prettier. **Owed:** a visual/manual
+  pass on the live edit flow (the toolbar action, the "Editing" banner, Save changes).
+
 - **2026-06-13 (guidance: reason over role, not raw type)** — closed a **false-positive class**
   in `builderWarnings` (eng-council + council consult). A histogram (bar, binned-Q X, count Y)
   tripped "two measures → scatter" because `isMeasureMapping`/`effectiveType` ignored `bin`.
@@ -599,8 +625,8 @@ Phase 2  2A value-or-field channels (Property model)  ✓ done
          2B field shelf + in-place type cycling       ✓ done (field-first + on-chart shelves)
 Phase 3  3D entry points & discoverability         ✓ done (2026-06-12)
          3A intent-first front door (Tier C)       ✓ done (2026-06-13); persistent strip
-         3B starter examples                       ← next; pairs with 3C
-         3C open in builder (strict hydration)     ← added 2026-06-11; pairs with 3B
+         3C open in builder (strict hydration)     ✓ done (2026-06-18); edit-in-place
+         3B starter examples                       ← next; now hydrates via 3C
 Marks    +rect (Heatmap)                           ✓ done (2026-06-13)
 Phase 4  (gated) theta/facets/styling-overrides/undo/lookup — decide after Phase 3