feat(2.0): inset axes — qv.Inset as a structural element + pane [D152]–[D154]

CHANGELOG.md

@@ -8,6 +8,21 @@ All notable changes to qtviz are documented here. The format follows
 
 ### Added
 
+- **Inset axes ([D152]–[D154], `design/inset-axes.md`):** `qv.Inset(child,
+  rect=(x0, y0, w, h), label=…, indicate=…)` — a child surface floating on a
+  parent, composed like an annotation: `overview * qv.Inset(zoom,
+  rect=(0.55, 0.55, 0.4, 0.4), label="zoom")`. `rect` is axes-fraction of
+  the parent's plot area; the child is a full surface (own title, lims,
+  scales via `.opts()`). On `Inset`, `label=` is the **pane label** (an
+  inset has no legend entry — it is chrome, like annotations): a labeled
+  inset is a pane, so its zoom window survives rebuilds and backend
+  switches via `LayoutState`, `view.pane("zoom").set_range(…)` drives it,
+  events from inside it carry `pane="zoom"`, and `pane.export(…)` writes
+  just the inset. `indicate=True` draws the parent-side rectangle marking
+  the child's declared x/y window. Rendered natively on pyqtgraph and
+  matplotlib; the webengine backend warns and skips insets for now (the
+  parent renders normally).
+
 - **Structured axis sharing ([D146]):** `link_x`/`link_y` widen from bools to
   `bool | "col" | "row"` — `True` links all panes (unchanged), `"col"`/`"row"`
   link within each grid column/row, with spanning panes merging groups

CLAUDE.md

@@ -38,7 +38,7 @@ Test markers: `tier1` (pure core, no QApplication), `tier2` (Qt event loop + bac
 Layering (strict, one-directional — core never imports a concrete backend):
 
 - **`src/qtviz/core/`** — the spec's abstractions: `Element` (immutable, value-hashed, Qt-free declarative data), the **Mark IR** ([D121]/[D122]: `marks.py` — 9 typed drawing primitives in linear data space; `lowering.py` — `Element.lower(ctx) -> Lowered`), `Backend` protocol + `RenderContext`/`RenderHandle`/`ViewState` (`core/backend.py`), composition via operators (`a * b` → `Overlay`, `a + b` → `Layout`, in `compose.py`) with `.opts()` surface sugar ([D133]), `View` + `show()` (`core/view.py`), `Theme`/`Palette`/`Color`/`Norm`, typed events on an `EventBus`, `Capabilities` and backend negotiation, threading discipline.
-- **`src/qtviz/elements/`** — the 28 element classes. Pure data constructors; a **tail of 14 lowers** (Quiver, Streamlines, Stem, Spread, Ecdf + the 9 annotations: one `lower()` in core, zero backend edits) and **14 stay native** (Scatter, Curve, Bars, Histogram, Area, BoxPlot, Violin, Image, Heatmap, Mesh, Contour, ErrorBars, Pie, RawFigure — engine idioms a lowering would visibly change; rationale in the 2.0 doc §8).
+- **`src/qtviz/elements/`** — the 29 element classes. Pure data constructors; a **tail of 14 lowers** (Quiver, Streamlines, Stem, Spread, Ecdf + the 9 annotations: one `lower()` in core, zero backend edits), **14 stay native** (Scatter, Curve, Bars, Histogram, Area, BoxPlot, Violin, Image, Heatmap, Mesh, Contour, ErrorBars, Pie, RawFigure — engine idioms a lowering would visibly change; rationale in the 2.0 doc §8), and **Inset** ([D152]) is structural — a child surface drawn in the backends' surface loop, its labeled pane riding the [D147] machinery.
 - **`src/qtviz/data/`** — container-agnostic data layer. `DataRef` (tabular vs gridded), a priority-ordered adapter registry (dict/NumPy/pandas/Arrow eager; dask/xarray/zarr lazy), channel **accessors** (column name, serializable `Expression` via `col()`/`lit()`, callable, or raw array — **every channel keyword takes the full union, never just column names**), streaming sources, viewport regridding. `resolve_node` dispatches on `Element.DATA_KIND`; big-data side-channels ride the typed `_aux` slot (`RasterAux`/`GridAux`, [D124]).
 - **`src/qtviz/backends/{pyqtgraph,matplotlib,webengine}/`** — each implements the `Backend` protocol and registers through the **`qtviz.backends` entry-point group** ([D125]; a third-party backend needs zero qtviz edits). Each has a `_marks.py` adapter (~8 drawers, written once) for lowered elements — the pyqtgraph adapter is the one place its log pretransform lives — plus native renderers for the head elements; **a registered native renderer wins over lowering** (the fast-path override). Each maps `ViewState` to/from native ranges so pan/zoom/selection survive backend switches. The webengine backend hosts a Qt↔JS bridge (`core/`) with library extensions (`ext/`); `_runtime.py` files there are JavaScript embedded as Python strings (ruff E501 ignored, excluded from coverage).
 - **`src/qtviz/adapter/`** (holoviews/hvplot ingestion) and **`src/qtviz/ext/`** (datashader: large data → screen-resolution rasters that re-aggregate on zoom).