fix(driver): pin polar api version

docs/windows-driver.md

@@ -352,6 +352,12 @@ portal URL changes, then rebuild the Windows package. No Polar access token or
 webhook secret is compiled into the client:
 activation, validation, and deactivation use Polar's
 [public customer license-key API](https://polar.sh/docs/features/benefits/license-keys).
+Those requests pin Polar's date-based API contract to `2026-04` with the
+`Polar-Version` header. Before Polar removes that version, update
+`polar_request_headers` in
+`src/platform/windows/broker/libvirtualhid_broker.cpp`, review Polar's
+[API versioning guidance](https://polar.sh/docs/api-reference/versioning), and
+validate the license response contract before rebuilding the Windows package.
 
 The production configuration accepts organization
 `3db9f05a-44d7-42f1-ba7c-a0f198235fb7` with yearly license-key benefit

src/platform/windows/broker/libvirtualhid_broker.cpp

@@ -80,6 +80,10 @@ namespace lvh::detail::windows_broker_service {
   constexpr int polar_connect_timeout = 5000;
   constexpr int polar_send_timeout = 5000;
   constexpr int polar_receive_timeout = 10000;
+  constexpr auto polar_request_headers =
+    L"Accept: application/json\r\n"
+    L"Content-Type: application/json\r\n"
+    L"Polar-Version: 2026-04\r\n";
   constexpr auto license_validation_interval = std::chrono::days {1};
   constexpr auto license_validation_retry_interval = std::chrono::seconds {60};
   constexpr auto license_outage_device_retention = std::chrono::hours {1};
@@ -944,8 +948,7 @@ namespace lvh::detail::windows_broker_service {
       return result;
     }
 
-    auto body = request_body.dump(-1, ' ', false, nlohmann::json::error_handler_t::replace);
-    if (constexpr auto headers = L"Accept: application/json\r\nContent-Type: application/json\r\n"; ::WinHttpSendRequest(request.get(), headers, static_cast<DWORD>(-1), body.data(), static_cast<DWORD>(body.size()), static_cast<DWORD>(body.size()), 0) == FALSE) {
+    if (auto body = request_body.dump(-1, ' ', false, nlohmann::json::error_handler_t::replace); ::WinHttpSendRequest(request.get(), polar_request_headers, static_cast<DWORD>(-1), body.data(), static_cast<DWORD>(body.size()), static_cast<DWORD>(body.size()), 0) == FALSE) {
       result.error = "WinHttpSendRequest failed: " + windows_error_message(::GetLastError());
       return result;
     }

tests/fixtures/include/fixtures/windows_broker_service_test_hooks.hpp

@@ -48,6 +48,7 @@ namespace lvh::detail::test {
     int connect_timeout = 0;
     int send_timeout = 0;
     int receive_timeout = 0;
+    std::wstring request_headers;
     std::string body;
     std::string error;
   };

tests/fixtures/windows_broker_service_test_hooks.cpp

@@ -48,6 +48,7 @@ namespace {
     int connect_timeout = 0;
     int send_timeout = 0;
     int receive_timeout = 0;
+    std::wstring request_headers;
   };
 
   BrokerServiceTestState &broker_service_test_state() {
@@ -285,14 +286,22 @@ namespace {
 
   BOOL WINAPI broker_test_win_http_send_request(
     HINTERNET,
-    LPCWSTR,
-    DWORD,
+    LPCWSTR headers,
+    DWORD headers_length,
     std::byte *,
     DWORD,
     DWORD,
     DWORD_PTR
   ) {
-    if (broker_service_test_state().polar_scenario == BrokerPolarScenario::send_failure) {
+    auto &state = broker_service_test_state();
+    if (headers == nullptr) {
+      state.request_headers.clear();
+    } else if (headers_length == static_cast<DWORD>(-1)) {
+      state.request_headers = headers;
+    } else {
+      state.request_headers.assign(headers, headers_length);
+    }
+    if (state.polar_scenario == BrokerPolarScenario::send_failure) {
       ::SetLastError(ERROR_WINHTTP_CONNECTION_ERROR);
       return FALSE;
     }
@@ -466,6 +475,7 @@ namespace lvh::detail::test {
     state.connect_timeout = 0;
     state.send_timeout = 0;
     state.receive_timeout = 0;
+    state.request_headers.clear();
     const auto result =
       lvh::detail::windows_broker_service::post_polar_license_request(
         L"/test",
@@ -480,6 +490,7 @@ namespace lvh::detail::test {
       .connect_timeout = state.connect_timeout,
       .send_timeout = state.send_timeout,
       .receive_timeout = state.receive_timeout,
+      .request_headers = state.request_headers,
       .body = result.body,
       .error = result.error,
     };

tests/unit/test_windows_broker_service.cpp

@@ -395,6 +395,7 @@ TEST(WindowsBrokerImplementationTest, ReportsDpapiAndPolarFailures) {
   EXPECT_EQ(succeeded.connect_timeout, 5000);
   EXPECT_EQ(succeeded.send_timeout, 5000);
   EXPECT_EQ(succeeded.receive_timeout, 10000);
+  EXPECT_NE(succeeded.request_headers.find(L"Polar-Version: 2026-04\r\n"), std::wstring::npos);
 }
 
 TEST(WindowsBrokerImplementationTest, BoundsOfflineSubscriptionValidation) {