whatsapp: native C++ client + terminal-screenshot tool

Native WhatsApp Web multi-device client in C++ (src/whatsapp/, namespace
detz::wa), built on OpenSSL plus a vendored public-domain ed25519 ref10
(third_party/ed25519, zlib) for XEdDSA and the nayuki QR generator
(third_party/qrcodegen, MIT); no new runtime dependency.

- WaCrypto, WaBinary, WaProto, WaNoise, WaSignal, WaDevice, WaSocket,
  WaClient, WaStore, WaQr, WaWizard.
- Verified offline against golden vectors captured from the real Baileys
  client (tests/whatsapp_data, from jfelipesjc/wa-go, MIT): HKDF/PBKDF2 RFC
  vectors, XEdDSA roundtrips, codec battery 19/19, ClientPayload byte-exact,
  the Noise handshake, and a 4-exchange Signal session byte-exact. Unit test
  build/whatsapp_test (16/16), run_all step whatsapp.unit.
- Verified live against web.whatsapp.com: `detz --whatsapp-link` connects,
  completes the Noise handshake, receives pair-device, renders a scannable QR
  in the terminal, and persists the device to the vault (whatsapp/<profile>.db).
  Also --whatsapp-status / --whatsapp-unlink.
- Agent tools whatsapp_send and whatsapp_contacts (detz-only, in DetzTools).
- Pairing completion after the phone scans, and the message send path
  (usync + prekey fetch + Signal encrypt + send node), are ported faithfully
  from whatsmeow but unverified in-tree (no linked account in development).
  send_image and own-device fan-out are not wired yet. See docs/whatsapp.md.

Also in this snapshot: the terminal-screenshot tool (src/termshot/,
terminal_screenshot, docs/termshot.md, research/terminal-screenshot-rendering)
and a concurrent session's in-progress llm/muse failover changes carried along
in the shared files.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

taicpp/tests/agent_diff.cpp

@@ -4,6 +4,7 @@
 #include "../src/agent/agent.h"
 #include "../src/agent/text.h"
 #include "../src/agent/data.h"
+#include "../src/agent/detz_tools.h"
 #include "../src/llm/chat_client.h"
 #include "../src/llm/cli_backends.h"
 #include "../src/llm/http_transport.h"
@@ -326,6 +327,7 @@ std::map<std::string, Fn> registry() {
 }  // namespace
 
 int main() {
+  agent::DetzTools::set_enabled(false);   // compare the tai.py tool set only
   auto reg = registry();
   std::string line;
   while (std::getline(std::cin, line)) {