diff --git a/build.sh b/build.sh
index 79e36a05..41d7940f 100755
--- a/build.sh
+++ b/build.sh
@@ -52,7 +52,7 @@ for tool in make sha256sum; do
     command -v "$tool" >/dev/null || { echo "ERROR: required tool not found: $tool" >&2; exit 1; }
 done
 read -r -a COMPILER <<< "${CC:-gcc}"
-command -v "${COMPILER[0]}" >/dev/null || { echo "ERROR: compiler not found: ${CC:-gcc}" >&2; exit 1; }
+COMPILER_PATH=$(command -v "${COMPILER[0]}") || { echo "ERROR: compiler not found: ${CC:-gcc}" >&2; exit 1; }
 COMPILER_ID=$("${COMPILER[@]}" --version) || { echo "ERROR: cannot identify compiler: ${CC:-gcc}" >&2; exit 1; }
 
 # Хеши учитывают содержимое и имена файлов, включая добавление/удаление макросов.
@@ -91,7 +91,7 @@ if command -v pkg-config >/dev/null && pkg-config --exists "${FFMPEG_PACKAGES[@]
     FFMPEG_LDFLAGS=$(pkg-config --libs-only-L "${FFMPEG_PACKAGES[@]}")
 fi
 request_sum=$({
-    printf '%s\0' "$MODE" "${OSTYPE:-}" "${MSYSTEM:-}" "${MSYSTEM_PREFIX:-}" "${CC:-gcc}" "$COMPILER_ID"
+    printf '%s\0' "$MODE" "${OSTYPE:-}" "${MSYSTEM:-}" "${MSYSTEM_PREFIX:-}" "${CC:-gcc}" "$COMPILER_PATH" "$COMPILER_ID"
     printf '%s\0' "${CFLAGS+x}" "${CFLAGS-}" "${CPPFLAGS+x}" "${CPPFLAGS-}" "${LDFLAGS+x}" "${LDFLAGS-}"
     printf '%s\0' "${LIBS+x}" "${LIBS-}" "${MAKEFLAGS-}" "${DEBUG_FLAGS+x}" "${DEBUG_FLAGS-}"
     printf '%s\0' "$FFMPEG_OPTION" "$FFMPEG_ID" "$FFMPEG_CFLAGS" "$FFMPEG_LDFLAGS"
diff --git a/tests/test_build_script.py b/tests/test_build_script.py
index 8cdb1939..f216fc0e 100644
--- a/tests/test_build_script.py
+++ b/tests/test_build_script.py
@@ -1,8 +1,8 @@
 #!/usr/bin/env python3
 """Проверка настоящего build.sh на маленьком проекте Autotools, без изменения исходников uTun."""
 from pathlib import Path
-import json
 import os
+import shlex
 import shutil
 import subprocess
 import sys
@@ -92,7 +92,9 @@ int main(void) { printf("%d\\n", worker() + fixture() + opus_fixture()); return
     write('src/worker.c', '#include "api.h"\nint worker(void) { return VALUE + LOCAL_OPTION; }\n')
     write('src/api.h', '#include "nested.h"\n')
     write('src/nested.h', '#define VALUE 10\n')
-    write('tests/Makefile.am', 'noinst_PROGRAMS = probe\nprobe_SOURCES = probe.c\n')
+    test_rules = (script.parent / 'tests/Makefile.am').read_text()
+    config_rules = test_rules[test_rules.index('all-local: copy-test-configs'):test_rules.index('# Test logs directory')]
+    write('tests/Makefile.am', 'noinst_PROGRAMS = probe\nprobe_SOURCES = probe.c\n' + config_rules)
     write('tests/probe.c', 'int main(void) { return 0; }\n')
     package_tool = write('bin/pkg-config', '''#!/bin/bash
 [[ "${BUILD_TEST_FFMPEG:-0}" = 1 ]] || exit 1
@@ -141,6 +143,14 @@ esac
     build('CFLAGS=-g -O0 -DUSER_OPTION=1')
     check('repeat build with quoted flags is incremental', initial == times())
     build()
+    gcc = shutil.which('gcc')
+    for directory in ['compiler-first', 'compiler-second']:
+        wrapper = write(directory + '/gcc', '#!/bin/bash\nexec ' + shlex.quote(gcc) + ' "$@"\n')
+        wrapper.chmod(0o755)
+    build(extra_environment={'PATH': str(base / 'compiler-first') + os.pathsep + environment['PATH']})
+    result = build(extra_environment={'PATH': str(base / 'compiler-second') + os.pathsep + environment['PATH']})
+    check('compiler path change is detected even with identical version', 'INFO: configuring:' in result.stdout)
+    build()
     time.sleep(1.1)
     write('src/Makefile.am', (base / 'src/Makefile.am').read_text().replace('LOCAL_OPTION=1', 'LOCAL_OPTION=2'))
     result = build()
@@ -161,8 +171,11 @@ esac
     write('src/.deps/worker.Po', '# dummy\n')
     result = build()
     check('dummy dependencies force rebuild', 'missing_dependencies=1' in result.stdout)
+    write('tests/test_preserve.conf', 'preserve configuration\n')
+    write('tests/test_preserve.json', '{"preserve":true}\n')
     result = build('--clean')
     check('explicit clean does not reconfigure', 'INFO: cleaning objects:' in result.stdout and 'INFO: configuring:' not in result.stdout)
+    check('in-source clean preserves configuration files', (base / 'tests/test_preserve.conf').exists() and (base / 'tests/test_preserve.json').exists())
     result = build('--full')
     check('explicit full regenerates, configures and rebuilds', 'INFO: regenerating' in result.stdout and 'INFO: configuring:' in result.stdout)
     (base / 'src/Makefile').unlink()
@@ -191,6 +204,19 @@ esac
     result = run(['bash', 'build.sh', '-j', '3'], ok=False)
     check('GUI failure propagates and success is not printed', result.returncode != 0 and 'Build completed successfully!' not in result.stdout)
     check('GUI receives selected job count', (base / 'gui-arguments').read_text().strip() == '--build tools/chatgui/build --parallel 3')
+    run(['make', 'distclean'])
+    output_dir = base / 'out'
+    output_dir.mkdir()
+    for args in [['../configure'], ['make', '-j2'], ['make', '-C', 'tests', 'clean-local']]:
+        result = subprocess.run(args, cwd=output_dir, env=environment, capture_output=True, text=True)
+        with log.open('a') as output:
+            output.write(f'OUT-OF-TREE {args!r}\nexit={result.returncode}\n{result.stdout}{result.stderr}\n')
+        if result.returncode:
+            raise AssertionError(f'out-of-tree {args!r}: see {log}')
+        if args[0] == 'make' and '-j2' in args:
+            check('out-of-tree build copies test configurations', (output_dir / 'tests/test_preserve.conf').exists())
+    check('out-of-tree clean removes copies and preserves source configurations',
+          not (output_dir / 'tests/test_preserve.conf').exists() and (base / 'tests/test_preserve.conf').exists())
     print(f'[PASS] build.sh: {len(checks)} checks completed', flush=True)
     shutil.rmtree(base)
 except Exception: