feat(real-world-vfc-slice): add labeled OpenSSL/Firefox/Chromium/curl pair corpus

Harvest 176 isolated vuln-vs-fix functions (109 CVEs, 352 training rows)
into benchmarks/pairs/vfc with provenance and a JSONL training manifest.
Score the slice as an honesty dashboard (ousast pairs --slice vfc);
keep the pair gate on the local fixtures only.

benchmarks/pairs/vfc/chromium-cve-2019-5786/fixed.cc

@@ -0,0 +1,67 @@
+/* Provenance: Chromium FileReaderLoader::ArrayBufferResult after CVE-2019-5786.
+ * repo: chromium/chromium
+ * commit: ba9748e78ec7e9c0d594e7edf7b2c07ea2a90449
+ * parent: 9f3fccdba567f30ea39b08f57d8d5b49cd832b4a
+ * commit_url: https://github.com/chromium/chromium/commit/ba9748e78ec7e9c0d594e7edf7b2c07ea2a90449
+ * cve: CVE-2019-5786
+ * license: BSD-3-Clause
+ * function: FileReaderLoader::ArrayBufferResult
+ * relpath: third_party/blink/renderer/core/fileapi/file_reader_loader.cc
+ */
+#include <cstdint>
+#include <memory>
+
+enum class FileErrorCode { kOK };
+
+class ArrayBuffer {
+ public:
+    static void *Create(const void *data, size_t length) {
+        (void)data;
+        (void)length;
+        return nullptr;
+    }
+};
+
+class DOMArrayBuffer {
+ public:
+    static DOMArrayBuffer *Create(void *buffer) {
+        (void)buffer;
+        return nullptr;
+    }
+};
+
+struct RawData {
+    void *ToArrayBuffer() { return nullptr; }
+    size_t ByteLength() const { return 0; }
+    const void *Data() const { return nullptr; }
+};
+
+class FileReaderLoader {
+ public:
+    DOMArrayBuffer *ArrayBufferResult();
+
+    DOMArrayBuffer *array_buffer_result_ = nullptr;
+    std::unique_ptr<RawData> raw_data_;
+    FileErrorCode error_code_ = FileErrorCode::kOK;
+    bool finished_loading_ = false;
+
+    void AdjustReportedMemoryUsageToV8(int64_t delta) { (void)delta; }
+};
+
+DOMArrayBuffer *FileReaderLoader::ArrayBufferResult() {
+    if (array_buffer_result_)
+        return array_buffer_result_;
+
+    // If the loading is not started or an error occurs, return an empty result.
+    if (!raw_data_ || error_code_ != FileErrorCode::kOK)
+        return nullptr;
+
+    if (!finished_loading_) {
+        return DOMArrayBuffer::Create(ArrayBuffer::Create(raw_data_->Data(), raw_data_->ByteLength()));
+    }
+
+    array_buffer_result_ = DOMArrayBuffer::Create(raw_data_->ToArrayBuffer());
+    AdjustReportedMemoryUsageToV8(-1 * static_cast<int64_t>(raw_data_->ByteLength()));
+    raw_data_.reset();
+    return array_buffer_result_;
+}