feat: add Compiler::JsonIR for interscript-ts compatibility

Adds a new compiler that walks the AST and emits JSON IR consumed by
interscript-ts. Mirrors the structure of Compiler::Javascript but
produces data, not code.

## IR schema (v1)
- schemaVersion: 1
- systemCode, dependencies[], metadata, stages[], aliases, functions

## Stage serialisation
- Each Stage becomes { kind: 'stage', name, rules: [...] }
- Group::Parallel -> { kind: 'parallel', rules: [...] }
- Group::Sequential -> { kind: 'sequential', rules: [...] }

## Rule serialisation
- Sub: from/to/before/after/notBefore/notAfter/priority (omitted if nil)
- Run: stage name + resolved docName (dependency alias -> system code)
- Funcall: name + kwargs

## Item serialisation
- String, CaptureGroup, CaptureRef, Alias, Any, Group, Repeat, Stage

## Resolution
- Run rule's docName resolves via dep_aliases so consumers don't need
  the Ruby dep_aliases indirection

## Rakefile
- New task compile:json_ir (parallel to existing compile:javascript)

Refs: interscript/interscript#3

Author: ronaldtse

Rakefile

@@ -17,6 +17,9 @@ task :compile, [:compiler, :target] do |t, args|
   when "python"
     require "interscript/compiler/python"
     [Interscript::Compiler::Python, "py"]
+  when "json_ir"
+    require "interscript/compiler/json_ir"
+    [Interscript::Compiler::JsonIR, "json"]
   end
 
   FileUtils.mkdir_p(args[:target])

lib/interscript/compiler/json_ir.rb

@@ -0,0 +1,189 @@
+# frozen_string_literal: true
+
+require "json"
+
+# JSON IR compiler — emits a data-only intermediate representation consumable
+# by non-Ruby runtimes (e.g. interscript-ts). Unlike Compiler::Javascript,
+# which emits imperative JS that calls into a runtime, this emits a pure-data
+# JSON document describing the AST.
+#
+# The shape is versioned via SCHEMA_VERSION. Runtimes should refuse to load
+# IR with an unknown schema.
+class Interscript::Compiler::JsonIR < Interscript::Compiler
+  SCHEMA_VERSION = 1
+
+  CompiledResult = Struct.new(:code) do
+    # JsonIR output is already JSON. The runtime treats .code as opaque
+    # text; consumers parse via JSON.parse.
+    def to_json(*)
+      code
+    end
+  end
+
+  def compile(map, debug: false)
+    @map = map
+    @c = JSON.pretty_generate(serialise_document(map))
+    self
+  end
+
+  def code
+    @c
+  end
+
+  private
+
+  def serialise_document(doc)
+    {
+      schemaVersion: SCHEMA_VERSION,
+      systemCode: doc.name.to_s,
+      dependencies: doc.dependencies.map(&:full_name),
+      metadata: serialise_metadata(doc.metadata),
+      stages: serialise_stages(doc.stages),
+      aliases: serialise_aliases(doc.aliases),
+      functions: {}
+    }
+  end
+
+  def serialise_metadata(metadata)
+    return {} unless metadata
+    out = {}
+    metadata.data.each do |k, v|
+      out[k.to_s] = case v
+                    when Symbol then v.to_s
+                    else v
+                    end
+    end
+    out
+  end
+
+  def serialise_stages(stages)
+    # Document#stages returns Hash{name => Stage} for the document's own stages,
+    # but may also include imported stages. Iterate values and skip anything
+    # that isn't an Interscript::Node::Stage (e.g. imported Hash entries).
+    stages.values.map { |s| serialise_stage(s) if s.is_a?(Interscript::Node::Stage) }.compact
+  end
+
+  def serialise_stage(stage)
+    {
+      kind: "stage",
+      name: stage.name.to_s,
+      rules: stage.children.map { |r| serialise_rule(r) }
+    }
+  end
+
+  def serialise_rule(rule)
+    case rule
+    when Interscript::Node::Rule::Sub
+      serialise_sub_rule(rule)
+    when Interscript::Node::Rule::Run
+      serialise_run_rule(rule)
+    when Interscript::Node::Rule::Funcall
+      serialise_funcall_rule(rule)
+    when Interscript::Node::Group::Parallel
+      # Parallel rule groups contain sub-rules that are applied simultaneously.
+      # In IR, we emit them as a marker rule so the runtime can decide.
+      {
+        kind: "parallel",
+        rules: rule.children.map { |r| serialise_rule(r) }
+      }
+    when Interscript::Node::Group::Sequential
+      {
+        kind: "sequential",
+        rules: rule.children.map { |r| serialise_rule(r) }
+      }
+    else
+      raise Interscript::MapLogicError, "Cannot serialise rule of type #{rule.class}"
+    end
+  end
+
+  def serialise_sub_rule(rule)
+    out = {kind: "sub"}
+    out[:from] = serialise_item(rule.from) if rule.from
+    out[:to] = serialise_to(rule.to)
+    out[:before] = serialise_item(rule.before) if rule.before
+    out[:after] = serialise_item(rule.after) if rule.after
+    out[:notBefore] = serialise_item(rule.not_before) if rule.not_before
+    out[:notAfter] = serialise_item(rule.not_after) if rule.not_after
+    out[:priority] = rule.priority if rule.priority
+    out
+  end
+
+  def serialise_run_rule(rule)
+    stage = rule.stage
+    doc_name = stage.map
+    if doc_name && @map.respond_to?(:dep_aliases) && @map.dep_aliases[doc_name.to_sym]
+      resolved = @map.dep_aliases[doc_name.to_sym].document
+      doc_name = resolved.name.to_s if resolved && resolved.respond_to?(:name)
+    end
+    {
+      kind: "run",
+      stage: stage.name.to_s,
+      docName: doc_name&.to_s
+    }
+  end
+
+  def serialise_funcall_rule(rule)
+    {
+      kind: "funcall",
+      name: rule.name.to_s,
+      kwargs: symbolise_keys(rule.kwargs)
+    }
+  end
+
+  def serialise_to(to)
+    case to
+    when Symbol
+      {kind: "funcall_inline", name: to.to_s}
+    else
+      serialise_item(to)
+    end
+  end
+
+  def serialise_item(item)
+    case item
+    when Interscript::Node::Item::String
+      {kind: "string", value: item.data}
+    when Interscript::Node::Item::CaptureGroup
+      {kind: "capture_group", data: serialise_item(item.data)}
+    when Interscript::Node::Item::CaptureRef
+      {kind: "capture_ref", id: item.id}
+    when Interscript::Node::Item::Alias
+      out = {kind: "alias", name: item.name.to_s}
+      out[:map] = item.map if item.map
+      out
+    when Interscript::Node::Item::Any
+      data = item.data || []
+      {kind: "any", of: data.map { |i| serialise_item(i) }}
+    when Interscript::Node::Item::Group
+      {kind: "group", items: item.children.map { |i| serialise_item(i) }}
+    when Interscript::Node::Item::Repeat
+      {kind: "repeat", item: serialise_item(item.data), min: 0, max: Float::INFINITY}
+    when Interscript::Node::Item::Stage
+      {kind: "stage_ref", name: item.name.to_s}
+    when nil
+      nil
+    else
+      raise Interscript::MapLogicError, "Cannot serialise item of type #{item.class}"
+    end
+  end
+
+  def capture_index(_item)
+    # CaptureGroup index is determined by position in pattern compilation.
+    # Runtimes should treat as a placeholder; the actual index is computed
+    # during pattern compilation based on capture-group ordering.
+    0
+  end
+
+  def serialise_aliases(aliases)
+    out = {}
+    aliases.each do |name, defn|
+      out[name.to_s] = serialise_item(defn.data)
+    end
+    out
+  end
+
+  def symbolise_keys(hash)
+    return {} if hash.nil?
+    hash.transform_keys(&:to_s)
+  end
+end