Core: classify spec data blocks by Vega-Lite fidelity (spec-data) for dataset refs

docs/exploration/multi-view-data-model-scope.md

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+# Multi-view data model — scope & plan
+
+Astrolabe authors arbitrary Vega-Lite, including **composed** specs (`layer`,
+`hconcat`/`vconcat`/`concat`, `facet`, `repeat`). Most of the spec-structure
+machinery already handles composition; the data-facing features carried
+single-view assumptions. This memo records the assessment, the data-model
+contract that anchors the work, and the milestone plan to make multi-view support
+durable. The guiding constraint: **extend Vega-Lite, never break it** — every
+native data form must keep working.
+
+## The data-model contract
+
+A dataset reference is exactly Vega-Lite **named data**: a `data` block with a
+string `name` and no `values`/`url`/generator key, whose name the spec does not
+self-define via top-level `datasets`. This mirrors Vega-Lite's `isNamedData`
+(`reference/vega-lite/src/data.ts`). The classification is owned by
+`core/spec-data` (`classifyData`, `libraryRefName`); reference extraction
+(`spec-refs`), rename (`spec-refs`), and render-time resolution (`rendering`) all
+route through it. See `docs/architecture/07` §3.1.
+
+Library references resolve to inline data before embedding
+(`core/rendering` → `prepareSpecForRender`); a self-defined `datasets` name is
+left for Vega-Lite to resolve natively.
+
+## Assessment: already multi-view vs. single-view assumptions
+
+**Already composition-aware** (recurse all view operators): ref extraction/rename
+(`spec-refs`), reference resolution + fit-mode (`rendering`), structural wrap/
+unwrap/add-view (`spec-transforms`, `spec-cursor`, `spec-insert`), derived-field
+collection (`spec-fields`), config baking (`spec-config`), standalone export
+(`chart-export`, reuses `prepareSpecForRender`).
+
+**Single-view assumptions** (the work):
+
+- **Editor data context** (`app/services/active-dataset`) resolves _one_ dataset
+  for the whole draft (first ref, or first inline data), with no notion of which
+  view the cursor sits in. Completion/hover/inlay (`spec-dataset-hints`) and the
+  facet/repeat field defaults (`spec-transform-actions`) therefore offer the wrong
+  view's columns in a composition whose views bind different datasets.
+- **Extract inline data** (`app/stores/ExtractStore`) lifts only the top-level
+  `data` block.
+- **Data inspector** (`core/result-data`, `DataInspector`) surfaces one input +
+  one resolved table; a composition produces several `source_<n>`/`data_<n>`.
+- **`deriveSnippetName`** (`core/snippet`) reads top-level `mark`/`encoding` only,
+  so a composed spec falls back to the default name (graceful, not a bug).
+- **Chart builder** is single-view by design; its strict round-trip hydration
+  returns `null` for composed specs, so they stay Monaco-only (correct).
+
+## Vega-Lite fidelity clashes
+
+1. **Named inline/url data misread as a reference** — classifying on "has a
+   string `name`" alone caught named-inline (`{ name, values }`) and named-url,
+   breaking valid specs (spurious `DatasetNotFoundError`, or clobbered inline
+   values). _Resolved_ by the `core/spec-data` classifier (M1).
+2. **Shadowing** — a library dataset whose name equals a self-defined `datasets`
+   key is silently ignored (self-defined wins). Documented precedence; candidate
+   for a user-facing note, no code change required.
+3. **Case-rule split** — library matching is case-insensitive (`naming.ts`);
+   self-defined exclusion and Vega-Lite's own named-data lookup are case-sensitive.
+   These are distinct namespaces, so the split is defensible; minor.
+4. **Runtime-injected named data** — Vega-Lite allows binding `{ name }` at
+   runtime; Astrolabe always pre-resolves, so an imported spec relying on runtime
+   injection won't render. Out of scope.
+
+## Milestone plan
+
+- **M1 — data-model foundation** ✅ — `core/spec-data` classifier mirroring
+  `isNamedData`; `spec-refs` + `rendering` routed through it. Closes clash 1.
+- **M2 — view-scoped editor context** — pure `dataContextAtPath(spec, path)`:
+  climb the cursor's JSON path to the nearest enclosing `data` (honoring
+  Vega-Lite's parent→child data inheritance), classify it, and collect
+  ancestor-chain derived fields. Rework `active-dataset` to be cursor-scoped and
+  thread the offset through the three Monaco providers and the facet/repeat
+  defaults. Resolve columns for every form: library ref, inline `values`,
+  named-inline, self-defined `datasets`, url (no static rows), generator (none).
+- **M3 — view-scoped extract** — seed Extract from the focused view's inline data
+  (reusing the cursor-scope machinery) and rewrite that view's `data`.
+- **M4 — multi-view inspection** — group the dataflow's datasets into per-view
+  input/resolved pairs (`result-data`) and add a view selector to `DataInspector`
+  (new interactive widget → `/council`).
+
+Delivery is incremental, one milestone per commit, verified against real behavior.
+The consolidated data-model contract write-up into `docs/architecture` (05/08)
+lands once the shape is final.