feat(isc): ISC ↔ YAML round-trip via lutaml-model

Adds three new components:

1. Model layer (lib/interscript/isc/model/) — 9 lutaml-model classes
   mirroring the ISC document hash: Document, Metadata (open hash),
   Test, Alias, Stage, StageItem, Rule, Constraint, Item (polymorphic
   with 12 discriminated types)

2. YamlBridge (lib/interscript/isc/yaml_bridge.rb) — converts between
   document hash and lutaml-model objects in both directions

3. Serializer (lib/interscript/isc/serializer.rb) — converts document
   hash back to ISC source text, handling all item types including
   Set (any()), Concat (+), CaptureGroup (capture()), constraints,
   parallel/sequence blocks, run directives, compose, string_case

API:
  yaml = Isc::YamlBridge.to_yaml(doc_hash)
  doc = Isc::YamlBridge.from_yaml(yaml)
  isc = Isc::Serializer.serialize(doc_hash)

Round-trip verified: ISC → YAML → ISC → parse produces equivalent
document hash for alalc-amh-Ethi-Latn-1997.

Author: ronaldtse

lib/interscript/isc.rb

@@ -11,6 +11,9 @@ module Isc
     autoload :Items, "interscript/isc/items"
     autoload :Codemod, "interscript/isc/codemod"
     autoload :NodeAdapter, "interscript/isc/node_adapter"
+    autoload :Model, "interscript/isc/model"
+    autoload :YamlBridge, "interscript/isc/yaml_bridge"
+    autoload :Serializer, "interscript/isc/serializer"
 
     SCHEMA_VERSION = 1
 

lib/interscript/isc/model.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require "lutaml/model"
+
+module Interscript
+  module Isc
+    module Model
+      autoload :Item, "interscript/isc/model/item"
+      autoload :Constraint, "interscript/isc/model/constraint"
+      autoload :Rule, "interscript/isc/model/rule"
+      autoload :StageItem, "interscript/isc/model/stage_item"
+      autoload :Stage, "interscript/isc/model/stage"
+      autoload :Alias, "interscript/isc/model/alias"
+      autoload :Test, "interscript/isc/model/test"
+      autoload :Dependency, "interscript/isc/model/dependency"
+      autoload :Document, "interscript/isc/model/document"
+    end
+  end
+end

lib/interscript/isc/model/alias.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "lutaml/model"
+require "interscript/isc/model/item"
+
+module Interscript
+  module Isc
+    module Model
+      class Alias < Lutaml::Model::Serializable
+        attribute :name, :string
+        attribute :value, Item
+
+        yaml do
+          map "name", to: :name
+          map "value", to: :value
+        end
+      end
+    end
+  end
+end

lib/interscript/isc/model/constraint.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "lutaml/model"
+require "interscript/isc/model/item"
+
+module Interscript
+  module Isc
+    module Model
+      class Constraint < Lutaml::Model::Serializable
+        attribute :kind, :string
+        attribute :item, Item
+
+        yaml do
+          map "kind", to: :kind
+          map "item", to: :item
+        end
+      end
+    end
+  end
+end

lib/interscript/isc/model/dependency.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+require "lutaml/model"
+
+module Interscript
+  module Isc
+    module Model
+      class Dependency < Lutaml::Model::Serializable
+        attribute :target, :string
+        attribute :alias_name, :string
+
+        yaml do
+          map "target", to: :target
+          map "alias", to: :alias_name
+        end
+      end
+    end
+  end
+end

lib/interscript/isc/model/document.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require "lutaml/model"
+require "interscript/isc/model/test"
+require "interscript/isc/model/alias"
+require "interscript/isc/model/stage"
+require "interscript/isc/model/dependency"
+
+module Interscript
+  module Isc
+    module Model
+      class Document < Lutaml::Model::Serializable
+        attribute :system_code, :string
+        attribute :metadata, :hash
+        attribute :tests, Test, collection: true
+        attribute :aliases, Alias, collection: true
+        attribute :stages, Stage, collection: true
+        attribute :dependencies, Dependency, collection: true
+
+        yaml do
+          map "system_code", to: :system_code
+          map "metadata", to: :metadata
+          map "tests", to: :tests
+          map "aliases", to: :aliases
+          map "stages", to: :stages
+          map "dependencies", to: :dependencies
+        end
+      end
+    end
+  end
+end

lib/interscript/isc/model/item.rb

@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+require "lutaml/model"
+require "interscript/isc/model"
+
+module Interscript
+  module Isc
+    module Model
+      # Polymorphic representation of an ISC item (StringValue, AliasRef, etc.)
+      # Serialized as a discriminated union keyed by the `type` field.
+      #
+      # YAML shape:
+      #   type: string
+      #   value: "hello"
+      #   ---
+      #   type: alias_ref
+      #   name: my_alias
+      #   ---
+      #   type: concat
+      #   parts:
+      #     - type: string
+      #       value: "a"
+      #     - type: alias_ref
+      #       name: consonants
+      class Item < Lutaml::Model::Serializable
+        attribute :type, :string
+        attribute :value, :string
+        attribute :name, :string
+        attribute :index, :integer
+        attribute :lo, :string
+        attribute :hi, :string
+        attribute :chars, :string, collection: true
+        attribute :parts, Item, collection: true
+        attribute :inner, Item
+
+        yaml do
+          map "type", to: :type
+          map "value", to: :value
+          map "name", to: :name
+          map "index", to: :index
+          map "lo", to: :lo
+          map "hi", to: :hi
+          map "chars", to: :chars
+          map "parts", to: :parts
+          map "inner", to: :inner
+        end
+      end
+    end
+  end
+end

lib/interscript/isc/model/rule.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require "lutaml/model"
+require "interscript/isc/model/item"
+require "interscript/isc/model/constraint"
+
+module Interscript
+  module Isc
+    module Model
+      class Rule < Lutaml::Model::Serializable
+        attribute :from, Item
+        attribute :to, Item
+        attribute :constraints, Constraint, collection: true
+
+        yaml do
+          map "from", to: :from
+          map "to", to: :to
+          map "constraints", to: :constraints
+        end
+      end
+    end
+  end
+end

lib/interscript/isc/model/stage.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "lutaml/model"
+require "interscript/isc/model/stage_item"
+
+module Interscript
+  module Isc
+    module Model
+      class Stage < Lutaml::Model::Serializable
+        attribute :name, :string
+        attribute :body, StageItem, collection: true
+
+        yaml do
+          map "name", to: :name
+          map "body", to: :body
+        end
+      end
+    end
+  end
+end

lib/interscript/isc/model/stage_item.rb

@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+require "lutaml/model"
+require "interscript/isc/model/rule"
+require "interscript/isc/model/item"
+
+module Interscript
+  module Isc
+    module Model
+      # A single item in a stage body. Discriminated by `kind`:
+      #   parallel, sequence, bare_rule, run, separate, compose, string_case
+      class StageItem < Lutaml::Model::Serializable
+        attribute :kind, :string
+        attribute :rules, Rule, collection: true
+        attribute :rule, Rule
+        attribute :dependency, :string
+        attribute :stage, :string
+        attribute :separator, Item
+        attribute :op, :string
+
+        yaml do
+          map "kind", to: :kind
+          map "rules", to: :rules
+          map "rule", to: :rule
+          map "dependency", to: :dependency
+          map "stage", to: :stage
+          map "separator", to: :separator
+          map "op", to: :op
+        end
+      end
+    end
+  end
+end