Purity Ratchet

core/build.gradle

@@ -303,3 +303,42 @@ sourceSets {
         }
     }
 }
+
+tasks.register('bukkitPurityRatchet') {
+    group = 'verification'
+    description = 'Fails if files outside core/purity-allowlist.txt import org.bukkit (the allowlist only shrinks).'
+    File allowlistFile = project.file('purity-allowlist.txt')
+    File sourceRoot = project.file('src/main/java')
+    inputs.file(allowlistFile)
+    inputs.dir(sourceRoot)
+    doLast {
+        Set<String> allowed = allowlistFile.readLines().findAll { String line -> !line.isBlank() }.toSet()
+        List<String> offenders = new ArrayList<>()
+        List<String> coupled = new ArrayList<>()
+        sourceRoot.eachFileRecurse { File f ->
+            if (!f.name.endsWith('.java')) {
+                return
+            }
+            if (f.text.contains('org.bukkit')) {
+                String rel = sourceRoot.toPath().relativize(f.toPath()).toString()
+                coupled.add(rel)
+                if (!allowed.contains(rel)) {
+                    offenders.add(rel)
+                }
+            }
+        }
+        if (!offenders.isEmpty()) {
+            throw new GradleException("Bukkit purity ratchet violated - new org.bukkit coupling in:\n  " + offenders.join('\n  ') + "\nDecouple these files or (only with strong justification) add them to core/purity-allowlist.txt")
+        }
+        int shrunk = allowed.size() - coupled.size()
+        if (shrunk > 0) {
+            println("Purity ratchet: " + coupled.size() + " coupled files (" + shrunk + " fewer than allowlist - consider tightening core/purity-allowlist.txt)")
+        } else {
+            println("Purity ratchet: " + coupled.size() + " coupled files (at allowlist ceiling)")
+        }
+    }
+}
+
+tasks.named('check').configure {
+    dependsOn('bukkitPurityRatchet')
+}