Merge remote-tracking branch 'origin/feat/update' into dev

# Conflicts:
#	src/client/client_cli.c
#	src/client/usage.c
#	src/shared/file.c
#	src/shared/file.h
#	src/shared/file_receive.c
#	tests/test_client_cli.c

tests/integration/test_features.py

@@ -474,6 +474,61 @@ class TestIncremental:
         assert not mismatches, f"Mismatch: {mismatches}"
 
 
+class TestUpdate:
+    def test_update_skips_older_destination_and_allows_equal_or_newer_source(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+
+        received = get_dest_received_dir(DEST_DIR, SOURCE_DIR)
+        source_file = os.path.join(SOURCE_DIR, "small.txt")
+        received_file = os.path.join(received, "small.txt")
+        source_stat = os.stat(source_file)
+
+        with open(received_file, "wb") as f:
+            f.write(b"newer destination\n")
+        os.utime(received_file, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns + 10_000_000_000))
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+        with open(received_file, "rb") as f:
+            assert f.read() == b"newer destination\n"
+
+        os.utime(received_file, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns))
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+        with open(received_file, "rb") as f:
+            assert f.read() == b"hello world\n"
+
+    def test_update_skips_unreadable_newer_destination(self, shared_server):
+        clean_dir(DEST_DIR)
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+
+        received_file = os.path.join(get_dest_received_dir(DEST_DIR, SOURCE_DIR), "small.txt")
+        source_stat = os.stat(os.path.join(SOURCE_DIR, "small.txt"))
+        with open(received_file, "wb") as f:
+            f.write(b"protected destination\n")
+        os.utime(received_file, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns + 10_000_000_000))
+        original_mode = os.stat(received_file).st_mode
+        try:
+            os.chmod(received_file, 0)
+            result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+            assert result.returncode == 0
+            os.chmod(received_file, original_mode)
+            with open(received_file, "rb") as f:
+                assert f.read() == b"protected destination\n"
+        finally:
+            os.chmod(received_file, original_mode)
+
+        with open(received_file, "wb") as f:
+            f.write(b"older destination\n")
+        os.utime(received_file, ns=(source_stat.st_atime_ns, source_stat.st_mtime_ns - 10_000_000_000))
+        result, _ = run_client(SOURCE_DIR, DEST_DIR, flags=["-u"], port=shared_server.port)
+        assert result.returncode == 0
+        with open(received_file, "rb") as f:
+            assert f.read() == b"hello world\n"
+
+
 class TestDelete:
     def test_delete_removes_extra_files(self, shared_server):
         clean_dir(DEST_DIR)