Wrap corrupt cache reads in CacheCorruptError

lib/fixture_kit.rb

@@ -6,6 +6,7 @@ class DuplicateNameError < Error; end
   class InvalidFixtureDeclaration < Error; end
   class MultipleFixtures < Error; end
   class CacheMissingError < Error; end
+  class CacheCorruptError < Error; end
   class FixtureDefinitionNotFound < Error; end
   class RunnerAlreadyStartedError < Error; end
   class CircularFixtureInheritance < Error; end

lib/fixture_kit/file_cache.rb

@@ -33,6 +33,10 @@ def read
       end
 
       MemoryCache.new(data: data, exposed: exposed)
+    rescue JSON::ParserError, KeyError => e
+      raise FixtureKit::CacheCorruptError,
+        "FixtureKit cache file at #{path} is corrupt or malformed (#{e.class}: #{e.message}). " \
+        "Delete it and re-run to regenerate."
     end
 
     def write(data)

spec/unit/file_cache_spec.rb

@@ -83,6 +83,24 @@
 
       expect(File.exist?(nested_path)).to be(true)
     end
+
+    it "raises CacheCorruptError when the file contains invalid JSON" do
+      FileUtils.mkdir_p(cache_path)
+      File.write(file_path, "this is not json")
+
+      expect { file_cache.read }.to raise_error(FixtureKit::CacheCorruptError) do |error|
+        expect(error.message).to include(file_path)
+        expect(error.message).to include("JSON::ParserError")
+      end
+    end
+
+    it "raises CacheCorruptError when the JSON is missing required keys" do
+      FileUtils.mkdir_p(cache_path)
+      File.write(file_path, JSON.dump({ "data" => {} })) # no "exposed" key
+
+      expect { file_cache.read }
+        .to raise_error(FixtureKit::CacheCorruptError, /is corrupt or malformed.*KeyError/)
+    end
   end
 
   describe "#serialize_exposed" do