test(WO80/A4): normative rulings for parallel composition

Two rulings pinned as frozen vectors: a parallel block is single-pass
longest-match; duplicate rules resolve last-declared-wins. Each A4
ruling lands this way -- empirical vectors first, the IS-1 v2 normative
text accretes per ruled point.

Author: ronaldtse

spec/isc/semantics_spec.rb

@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+# WO80/A4 — normative rulings for the ISC semantic surface. Each vector
+# pins the reference behavior; IS-1 v2 documents these as normative
+# sections (the spec text accretes one section per ruled point).
+
+require "tmpdir"
+
+RSpec.describe "ISC semantics — parallel composition" do
+  def with_map(name, body)
+    dir = Dir.mktmpdir
+    File.write(File.join(dir, name), body)
+    Interscript.load_path.unshift(dir)
+    yield
+  ensure
+    Interscript.load_path.delete(dir) if dir
+  end
+
+  it "rules: a parallel block is single-pass longest-match" do
+    with_map("tst-long-1.isc", <<~ISC) do
+      system "TST:xx-Latn:Latn:1" {
+        metadata {
+          authority_id tst
+          id 1
+          language iso-639-2:xx
+          source_script Latn
+          destination_script Latn
+        }
+        stage main { parallel {
+          sub "b" "Y"
+          sub "ab" "X"
+        } }
+      }
+    ISC
+      expect(Interscript.transliterate("tst-long-1", "ab")).to eq("X")
+    end
+  end
+
+  it "rules: duplicate rules in a parallel resolve last-declared-wins" do
+    with_map("tst-tie-1.isc", <<~ISC) do
+      system "TST:xx-Latn:Latn:2" {
+        metadata {
+          authority_id tst
+          id 2
+          language iso-639-2:xx
+          source_script Latn
+          destination_script Latn
+        }
+        stage main { parallel {
+          sub "a" "1"
+          sub "a" "2"
+        } }
+      }
+    ISC
+      expect(Interscript.transliterate("tst-tie-1", "a")).to eq("2")
+    end
+  end
+end