Add source code.

include/Tokenizer.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <cstddef>
+#include <string>
+#include <vector>
+
+namespace Tokenizer {
+
+// Splits a command line on whitespace. Double quotes group words into a single
+// token ("Breeze A"). Throws std::invalid_argument on an unterminated quote.
+std::vector<std::string> split(const std::string& line);
+
+// Lenient split for tab completion: completed words, plus the word being typed.
+struct PartialLine {
+    std::vector<std::string> words;  // completed words (quotes removed)
+    std::string current;             // word being typed (quotes removed, may be empty)
+    std::size_t start = 0;           // index in the text where that word begins
+};
+
+PartialLine splitPartial(const std::string& text);
+
+}  // namespace Tokenizer