cli: faithful argparse port (single flag table, HelpFormatter, textwrap, abbreviations, usage on error)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

taicpp/tests/cli_driver.cpp

@@ -0,0 +1,42 @@
+// Parse-only driver for tests/cli_parity.py: behaves like detz for errors and -h, and for a
+// successful parse prints the argparse Namespace as sorted JSON (see docs/cli.md, Tests).
+#include <algorithm>
+#include <cstdio>
+#include <string>
+#include <vector>
+#include "../src/cli/arg_parser.h"
+#include "../src/cli/cli.h"
+using namespace detz::cli;
+namespace {
+std::string jstr(const std::string& s) {
+    std::string o = "\"";
+    for (unsigned char c : s) {
+        if (c == '"' || c == '\\') { o += '\\'; o += static_cast<char>(c); }
+        else if (c == '\n') o += "\\n";
+        else if (c < 0x20) { char b[8]; std::snprintf(b, sizeof b, "\\u%04x", c); o += b; }
+        else o += static_cast<char>(c);
+    }
+    return o + "\"";
+}
+}  // namespace
+int main(int argc, char** argv) {
+    Command cmd = Parser().parse(argc, argv);
+    if (!cmd.opts.error.empty() || cmd.opts.help) return cmd.run();
+    std::vector<std::string> args(argv + 1, argv + argc);
+    const ParseOutcome r = ArgParser{}.parse(args);
+    std::vector<std::pair<std::string, std::string>> kv;
+    for (auto& [k, v] : r.ns.flags) kv.push_back({k, v ? "true" : "false"});
+    for (auto& [k, v] : r.ns.strings) kv.push_back({k, jstr(v)});
+    for (auto& [k, v] : r.ns.numbers) kv.push_back({k, std::to_string(v)});
+    for (auto& [k, v] : r.ns.lists) {
+        if (k == "prompt" && v.empty()) continue;
+        std::string l = "[";
+        for (size_t i = 0; i < v.size(); ++i) { if (i) l += ", "; l += jstr(v[i]); }
+        kv.push_back({k, l + "]"});
+    }
+    std::sort(kv.begin(), kv.end());
+    std::string out = "{";
+    for (size_t i = 0; i < kv.size(); ++i) { if (i) out += ", "; out += jstr(kv[i].first) + ": " + kv[i].second; }
+    std::puts((out + "}").c_str());
+    return 0;
+}