schema: ludicc --emit-schema / ludic schema, --check --diagnostics=json, and editor attributes

--emit-schema FILE writes the compiler's resolved view once the program type-checks: every
record (fields, types, defaults as written, docs, places, attributes), every registry with its
entries in their final order after the open-registry merge (key, constant, index, file:line:col
of the entry and of each field value, and which file contributed which keys), every const, and
the zero-argument functions a fn value can name. Deterministic, schema_version 1; the runtime is
left out. `ludic schema [file] [-o FILE]` wraps it.

--check --diagnostics=json prints every error as one JSON array on stdout: the checker's and the
module rules' all, a parse or lowering error as the last. Tokens and nodes now carry a column.

Fields take several @attributes; @Ref(Registry), @OneOf(PREFIX_), @Range(lo, hi), @Unit("..."),
@Asset("..."), @Color on a field and @AppendOnly / @ByKey on a registry change nothing but go into
the schema, and @Ref naming no registry is an error (every one reported). Fixtures:
examples/lang/attributes.ludic, examples/rejected/ref_unknown.ludic, cases in ludic-dev test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/lang/attributes.ludic

@@ -0,0 +1,38 @@
+# attributes.ludic — editor metadata on the @-syntax: which registry a field indexes, which constants
+# it takes, its range, its unit, the kind of file it names, that it is a colour, and a registry's own
+# rules (append only, saved by key). None of them changes what the program does: `ludicc
+# --emit-schema` carries them to an editor with every record, registry entry and const. One is
+# checked - @Ref must name a registry that exists.
+#
+# Running it prints:  2 1 Lantern 2
+program Attributes {
+  # a shop in the valley
+  property Vendor {
+    key: string = ""
+    name: string = ""                          # what the sign over the counter says
+  }
+  @AppendOnly @ByKey
+  registry Vendors of Vendor as VD
+  def Vendors store { name: "General store" }
+  def Vendors marina { name: "Marina" }
+
+  # a tool a camp keeps
+  property Tool {
+    key: string = ""
+    name: string = ""
+    @Ref(Vendors) seller: int = 0              # who sells it
+    @Range(0, 20.5) @Unit("kg") weight: float = 1.0
+    @Asset("gltf")
+    model: string = ""                         # its model, under assets/kit
+    @Color tint: int = 16777215
+    @OneOf(VD_) stocked_at: int = VD_STORE
+  }
+  @AppendOnly
+  registry Tools of Tool as TL from "data/attr_tools.lres"
+  const CAMP_TOOLS: int = 2 * VD_COUNT         # how many a camp can carry
+  # the tool a new camp starts with
+  function first_tool() -> string { return Tools[0].name }
+  entry {
+    print(`{TL_COUNT} {Tools[TL_LANTERN].seller} {Tools[TL_LANTERN].name} {CAMP_TOOLS / 2}`)
+  }
+}

examples/lang/data/attr_tools.lres

@@ -0,0 +1,8 @@
+# attr_tools.lres - the tools attributes.ludic's registry reads when it is compiled
+axe { name: "Axe", seller: VD_STORE, weight: 1.5, model: "kit/axe.gltf" }
+lantern {
+  name: "Lantern"
+  seller: VD_MARINA
+  weight: 0.75
+  stocked_at: VD_MARINA
+}

examples/rejected/ref_unknown.ludic

@@ -0,0 +1,10 @@
+# attributes: @Ref names a registry - there is no registry Vendorz, nor Shops (both are reported)
+program R {
+  property Vendor { key: string = "" }
+  registry Vendors of Vendor
+  property Tool {
+    @Ref(Vendorz) seller: int = 0
+    @Ref(Shops) shop: int = 0
+  }
+  entry { print(VENDORS_COUNT) }
+}