bank tranfer fix

server/implementations/Catcrafts.Server-Transfer.cpp

@@ -369,6 +369,37 @@ std::unique_ptr<CreditSource> MakeFileCreditSource(std::filesystem::path path) {
     return std::make_unique<FileCreditSource>(std::move(path));
 }
 
+bool AppendCreditTo(const std::filesystem::path& creditsPath,
+                    const BankCredit& credit) {
+    if (credit.id.empty()) return false;
+    // Deduplicate on the bank's own payment id. bunq retries a callback about
+    // six times, and a periodic --pull-credits reads an overlapping window, so
+    // the SAME payment arrives more than once by design. Appending it twice
+    // would double the money against one reference — enough, on a part-paid
+    // order, to settle it without the balance ever arriving.
+    {
+        std::ifstream in(creditsPath, std::ios::binary);
+        std::string line;
+        while (std::getline(in, line)) {
+            if (line.empty()) continue;
+            const auto doc = Json::Parse(line);
+            if (!doc || !doc->IsObject()) continue;
+            if (doc->Str("id") == credit.id) return false;
+        }
+    }
+    std::ofstream out(creditsPath, std::ios::app | std::ios::binary);
+    if (!out) {
+        std::println(std::cerr, "transfer: cannot append to {}", creditsPath.string());
+        return false;
+    }
+    out << std::format(
+        R"({{"id":"{}","reference":"{}","amount_minor":{},"method":"{}"}})" "\n",
+        EscT(credit.id), EscT(credit.reference), credit.amountMinor,
+        EscT(credit.method));
+    out.flush();
+    return static_cast<bool>(out);
+}
+
 std::optional<int> PullCreditsInto(CreditSource& source,
                                    const std::filesystem::path& creditsPath) {
     const std::optional<std::vector<BankCredit>> fresh = source.Recent();