diff --git a/codegen/src/targets/native.rs b/codegen/src/targets/native.rs
index b08b401..a6fd86b 100644
--- a/codegen/src/targets/native.rs
+++ b/codegen/src/targets/native.rs
@@ -826,7 +826,9 @@ fn module_test(slug: &str, functions: &[&CompiledFunction]) -> Result<String> {
         .iter()
         .any(|function| matches!(function.core.output, Output::Struct(_)));
     let mut writer = Writer::new();
-    writer.write(format_args!("{HEADER}\n\n#ifdef IMPORT_UMBRELLA\nimport ptfkit;\n#else\nimport ptfkit.{slug};\n#endif\n\n#include \"support/close_enough.h\""));
+    writer.write(format_args!(
+        "{HEADER}\n\nimport ptfkit.{slug};\n\n#include \"support/close_enough.h\""
+    ));
     if type_traits {
         writer.write("\n#include <type_traits>\n\n");
     } else {
diff --git a/docs/src/contributing/development.md b/docs/src/contributing/development.md
index 42c884c..fa97085 100644
--- a/docs/src/contributing/development.md
+++ b/docs/src/contributing/development.md
@@ -131,6 +131,13 @@ These files have no generated-file marker and are not codegen outputs. Edit them
 directly when changing test infrastructure, then run the target verification
 suites. Keep the shared comparison policy consistent across targets.
 
+The handwritten native tests `tests/support/umbrella.c` and
+`tests/support/umbrella.cpp` check function and result-type access through
+`<ptfkit/ptfkit.h>` and `import ptfkit`, respectively. The C test is compiled as
+both C11 and C++23 and checks that all public headers can be included together.
+Generated verification tests use individual source headers or modules without
+repeating the suite through the umbrella.
+
 ### Adding a PTF
 
 The assisted workflow uses the skills in `.agents/skills/`:
diff --git a/targets/ptfkit-native/tests/CMakeLists.txt b/targets/ptfkit-native/tests/CMakeLists.txt
index d687c51..097eb08 100644
--- a/targets/ptfkit-native/tests/CMakeLists.txt
+++ b/targets/ptfkit-native/tests/CMakeLists.txt
@@ -3,16 +3,13 @@ function(ptfkit_add_native_tests case)
         PARSE_ARGV 1 arg
         ""
         ""
-        "SOURCES;LIBRARIES;DEFINITIONS;PROPERTIES;COMPILE_FEATURES"
+        "SOURCES;LIBRARIES;PROPERTIES;COMPILE_FEATURES"
     )
     foreach(source ${arg_SOURCES})
         get_filename_component(name ${source} NAME_WE)
         set(target ${case}_${name})
         add_executable(${target} ${source})
         target_link_libraries(${target} PRIVATE ${arg_LIBRARIES})
-        if(arg_DEFINITIONS)
-            target_compile_definitions(${target} PRIVATE ${arg_DEFINITIONS})
-        endif()
         if(arg_PROPERTIES)
             set_target_properties(${target} PROPERTIES ${arg_PROPERTIES})
         endif()
diff --git a/targets/ptfkit-native/tests/c/CMakeLists.txt b/targets/ptfkit-native/tests/c/CMakeLists.txt
index 2011601..8e89eba 100644
--- a/targets/ptfkit-native/tests/c/CMakeLists.txt
+++ b/targets/ptfkit-native/tests/c/CMakeLists.txt
@@ -1,8 +1,12 @@
 file(GLOB sources CONFIGURE_DEPENDS *.c)
 
 ptfkit_add_native_tests(c
-    SOURCES ${sources}
+    SOURCES ${sources} ../support/umbrella.c
     LIBRARIES ptfkit::c
 )
 
+set_target_properties(c_umbrella PROPERTIES
+    C_STANDARD 11 C_STANDARD_REQUIRED ON C_EXTENSIONS OFF
+)
+
 ptfkit_add_comparator_test(C c_comparator)
diff --git a/targets/ptfkit-native/tests/cpp/CMakeLists.txt b/targets/ptfkit-native/tests/cpp/CMakeLists.txt
index cdd1e23..69829e5 100644
--- a/targets/ptfkit-native/tests/cpp/CMakeLists.txt
+++ b/targets/ptfkit-native/tests/cpp/CMakeLists.txt
@@ -1,16 +1,8 @@
 file(GLOB sources CONFIGURE_DEPENDS *.cpp)
 
 ptfkit_add_native_tests(cpp
-    SOURCES ${sources}
+    SOURCES ${sources} ../support/umbrella.cpp
     LIBRARIES ptfkit::cpp
     PROPERTIES
         CXX_SCAN_FOR_MODULES ON
 )
-
-ptfkit_add_native_tests(cpp_umbrella
-    SOURCES ${sources}
-    LIBRARIES ptfkit::cpp
-    DEFINITIONS IMPORT_UMBRELLA
-    PROPERTIES
-        CXX_SCAN_FOR_MODULES ON
-)
diff --git a/targets/ptfkit-native/tests/cpp/ahuja1984.cpp b/targets/ptfkit-native/tests/cpp/ahuja1984.cpp
index 9465f67..1a85255 100644
--- a/targets/ptfkit-native/tests/cpp/ahuja1984.cpp
+++ b/targets/ptfkit-native/tests/cpp/ahuja1984.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.ahuja1984;
-#endif
 
 #include "support/close_enough.h"
 
diff --git a/targets/ptfkit-native/tests/cpp/aimrun2009.cpp b/targets/ptfkit-native/tests/cpp/aimrun2009.cpp
index 01362b4..604ee13 100644
--- a/targets/ptfkit-native/tests/cpp/aimrun2009.cpp
+++ b/targets/ptfkit-native/tests/cpp/aimrun2009.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.aimrun2009;
-#endif
 
 #include "support/close_enough.h"
 
diff --git a/targets/ptfkit-native/tests/cpp/beniaich2023.cpp b/targets/ptfkit-native/tests/cpp/beniaich2023.cpp
index 7dfe7a6..93219ca 100644
--- a/targets/ptfkit-native/tests/cpp/beniaich2023.cpp
+++ b/targets/ptfkit-native/tests/cpp/beniaich2023.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.beniaich2023;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/chakraborty2011.cpp b/targets/ptfkit-native/tests/cpp/chakraborty2011.cpp
index b027703..a980595 100644
--- a/targets/ptfkit-native/tests/cpp/chakraborty2011.cpp
+++ b/targets/ptfkit-native/tests/cpp/chakraborty2011.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.chakraborty2011;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/clapp1978.cpp b/targets/ptfkit-native/tests/cpp/clapp1978.cpp
index af6f2af..31034ab 100644
--- a/targets/ptfkit-native/tests/cpp/clapp1978.cpp
+++ b/targets/ptfkit-native/tests/cpp/clapp1978.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.clapp1978;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/cosby1984.cpp b/targets/ptfkit-native/tests/cpp/cosby1984.cpp
index e6949f4..612c69e 100644
--- a/targets/ptfkit-native/tests/cpp/cosby1984.cpp
+++ b/targets/ptfkit-native/tests/cpp/cosby1984.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.cosby1984;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/dharumarajan2019.cpp b/targets/ptfkit-native/tests/cpp/dharumarajan2019.cpp
index 0290f16..8ad0618 100644
--- a/targets/ptfkit-native/tests/cpp/dharumarajan2019.cpp
+++ b/targets/ptfkit-native/tests/cpp/dharumarajan2019.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.dharumarajan2019;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/dijkerman1988.cpp b/targets/ptfkit-native/tests/cpp/dijkerman1988.cpp
index 03d5af0..4467f04 100644
--- a/targets/ptfkit-native/tests/cpp/dijkerman1988.cpp
+++ b/targets/ptfkit-native/tests/cpp/dijkerman1988.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.dijkerman1988;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/ferrerjulia2004.cpp b/targets/ptfkit-native/tests/cpp/ferrerjulia2004.cpp
index fcc1539..a0f8176 100644
--- a/targets/ptfkit-native/tests/cpp/ferrerjulia2004.cpp
+++ b/targets/ptfkit-native/tests/cpp/ferrerjulia2004.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.ferrerjulia2004;
-#endif
 
 #include "support/close_enough.h"
 
diff --git a/targets/ptfkit-native/tests/cpp/gunarathna2019.cpp b/targets/ptfkit-native/tests/cpp/gunarathna2019.cpp
index 092daa2..952f489 100644
--- a/targets/ptfkit-native/tests/cpp/gunarathna2019.cpp
+++ b/targets/ptfkit-native/tests/cpp/gunarathna2019.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.gunarathna2019;
-#endif
 
 #include "support/close_enough.h"
 
diff --git a/targets/ptfkit-native/tests/cpp/hodnett2002.cpp b/targets/ptfkit-native/tests/cpp/hodnett2002.cpp
index 06dfa8f..f66c05b 100644
--- a/targets/ptfkit-native/tests/cpp/hodnett2002.cpp
+++ b/targets/ptfkit-native/tests/cpp/hodnett2002.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.hodnett2002;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/jabro1992.cpp b/targets/ptfkit-native/tests/cpp/jabro1992.cpp
index 3a1cba7..38e351a 100644
--- a/targets/ptfkit-native/tests/cpp/jabro1992.cpp
+++ b/targets/ptfkit-native/tests/cpp/jabro1992.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.jabro1992;
-#endif
 
 #include "support/close_enough.h"
 
diff --git a/targets/ptfkit-native/tests/cpp/lal1979.cpp b/targets/ptfkit-native/tests/cpp/lal1979.cpp
index 37a2f1c..f9134ed 100644
--- a/targets/ptfkit-native/tests/cpp/lal1979.cpp
+++ b/targets/ptfkit-native/tests/cpp/lal1979.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.lal1979;
-#endif
 
 #include "support/close_enough.h"
 
diff --git a/targets/ptfkit-native/tests/cpp/li2007.cpp b/targets/ptfkit-native/tests/cpp/li2007.cpp
index 957701b..f4c2d1a 100644
--- a/targets/ptfkit-native/tests/cpp/li2007.cpp
+++ b/targets/ptfkit-native/tests/cpp/li2007.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.li2007;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/mayr1999.cpp b/targets/ptfkit-native/tests/cpp/mayr1999.cpp
index a8dc624..7caef16 100644
--- a/targets/ptfkit-native/tests/cpp/mayr1999.cpp
+++ b/targets/ptfkit-native/tests/cpp/mayr1999.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.mayr1999;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/oosterveld1980.cpp b/targets/ptfkit-native/tests/cpp/oosterveld1980.cpp
index 41475ec..8bb44c2 100644
--- a/targets/ptfkit-native/tests/cpp/oosterveld1980.cpp
+++ b/targets/ptfkit-native/tests/cpp/oosterveld1980.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.oosterveld1980;
-#endif
 
 #include "support/close_enough.h"
 
diff --git a/targets/ptfkit-native/tests/cpp/pidgeon1972.cpp b/targets/ptfkit-native/tests/cpp/pidgeon1972.cpp
index c66ab99..821e734 100644
--- a/targets/ptfkit-native/tests/cpp/pidgeon1972.cpp
+++ b/targets/ptfkit-native/tests/cpp/pidgeon1972.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.pidgeon1972;
-#endif
 
 #include "support/close_enough.h"
 
diff --git a/targets/ptfkit-native/tests/cpp/puckett1985.cpp b/targets/ptfkit-native/tests/cpp/puckett1985.cpp
index bf4173b..ac6bfd4 100644
--- a/targets/ptfkit-native/tests/cpp/puckett1985.cpp
+++ b/targets/ptfkit-native/tests/cpp/puckett1985.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.puckett1985;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/rawls1982.cpp b/targets/ptfkit-native/tests/cpp/rawls1982.cpp
index 86b6222..cf684df 100644
--- a/targets/ptfkit-native/tests/cpp/rawls1982.cpp
+++ b/targets/ptfkit-native/tests/cpp/rawls1982.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.rawls1982;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/saxton2006.cpp b/targets/ptfkit-native/tests/cpp/saxton2006.cpp
index 1d02e3d..dc0d405 100644
--- a/targets/ptfkit-native/tests/cpp/saxton2006.cpp
+++ b/targets/ptfkit-native/tests/cpp/saxton2006.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.saxton2006;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/tiwary2014.cpp b/targets/ptfkit-native/tests/cpp/tiwary2014.cpp
index 2e8b147..bc722ef 100644
--- a/targets/ptfkit-native/tests/cpp/tiwary2014.cpp
+++ b/targets/ptfkit-native/tests/cpp/tiwary2014.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.tiwary2014;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/varallyai1982.cpp b/targets/ptfkit-native/tests/cpp/varallyai1982.cpp
index 112627a..6ccf835 100644
--- a/targets/ptfkit-native/tests/cpp/varallyai1982.cpp
+++ b/targets/ptfkit-native/tests/cpp/varallyai1982.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.varallyai1982;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/vereecken1989.cpp b/targets/ptfkit-native/tests/cpp/vereecken1989.cpp
index 37e0104..1af525f 100644
--- a/targets/ptfkit-native/tests/cpp/vereecken1989.cpp
+++ b/targets/ptfkit-native/tests/cpp/vereecken1989.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.vereecken1989;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/wang2012.cpp b/targets/ptfkit-native/tests/cpp/wang2012.cpp
index b8f3586..2089a54 100644
--- a/targets/ptfkit-native/tests/cpp/wang2012.cpp
+++ b/targets/ptfkit-native/tests/cpp/wang2012.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.wang2012;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/weber2020.cpp b/targets/ptfkit-native/tests/cpp/weber2020.cpp
index 5adec18..71a84f9 100644
--- a/targets/ptfkit-native/tests/cpp/weber2020.cpp
+++ b/targets/ptfkit-native/tests/cpp/weber2020.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.weber2020;
-#endif
 
 #include "support/close_enough.h"
 #include <type_traits>
diff --git a/targets/ptfkit-native/tests/cpp/zhao2016.cpp b/targets/ptfkit-native/tests/cpp/zhao2016.cpp
index 975aa29..1375ad5 100644
--- a/targets/ptfkit-native/tests/cpp/zhao2016.cpp
+++ b/targets/ptfkit-native/tests/cpp/zhao2016.cpp
@@ -1,10 +1,6 @@
 /* @generated by ptfkit-codegen; DO NOT EDIT. */
 
-#ifdef IMPORT_UMBRELLA
-import ptfkit;
-#else
 import ptfkit.zhao2016;
-#endif
 
 #include "support/close_enough.h"
 
diff --git a/targets/ptfkit-native/tests/cpp_fallback/CMakeLists.txt b/targets/ptfkit-native/tests/cpp_fallback/CMakeLists.txt
index 2114835..fcf54db 100644
--- a/targets/ptfkit-native/tests/cpp_fallback/CMakeLists.txt
+++ b/targets/ptfkit-native/tests/cpp_fallback/CMakeLists.txt
@@ -1,4 +1,5 @@
 file(GLOB sources CONFIGURE_DEPENDS ../c/*.c)
+list(APPEND sources "${CMAKE_CURRENT_SOURCE_DIR}/../support/umbrella.c")
 
 set_source_files_properties(
     ${sources}
@@ -12,3 +13,7 @@ ptfkit_add_native_tests(cpp_fallback
 )
 
 ptfkit_add_comparator_test(CXX cpp_comparator)
+
+set_target_properties(cpp_fallback_umbrella PROPERTIES
+    CXX_STANDARD 23 CXX_STANDARD_REQUIRED ON CXX_EXTENSIONS OFF
+)
diff --git a/targets/ptfkit-native/tests/support/umbrella.c b/targets/ptfkit-native/tests/support/umbrella.c
new file mode 100644
index 0000000..13b7077
--- /dev/null
+++ b/targets/ptfkit-native/tests/support/umbrella.c
@@ -0,0 +1,11 @@
+#include <ptfkit/ptfkit.h>
+
+#include "close_enough.h"
+
+int main(void) {
+    const saxton2006_ptf_result result = calc_ptf_saxton2006(0.88, 0.05, 2.5);
+    // Expected value from specs/functions/saxton2006.yaml, table_3_sand.
+    assert_close(result.theta_1500, 0.05022058, 0.001, 0.0, "volumetric_water_content",
+                 "volume_fraction", "registry", "table_3_sand");
+    return 0;
+}
diff --git a/targets/ptfkit-native/tests/support/umbrella.cpp b/targets/ptfkit-native/tests/support/umbrella.cpp
new file mode 100644
index 0000000..db4ec20
--- /dev/null
+++ b/targets/ptfkit-native/tests/support/umbrella.cpp
@@ -0,0 +1,12 @@
+import ptfkit;
+
+#include "close_enough.h"
+
+int main() {
+    const ptfkit::saxton2006::Saxton2006PTFResult result =
+        ptfkit::saxton2006::calc_ptf_saxton2006(0.88, 0.05, 2.5);
+    // Expected value from specs/functions/saxton2006.yaml, table_3_sand.
+    assert_close(result.theta_1500, 0.05022058, 0.001, 0.0, "volumetric_water_content",
+                 "volume_fraction", "registry", "table_3_sand");
+    return 0;
+}