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_e2e.cpp

@@ -3,6 +3,7 @@
 // the observable outcome as JSON. tests/agent_e2e.py runs the same scenario
 // through tai.py and compares.
 #include "../src/agent/agent.h"
+#include "../src/agent/detz_tools.h"
 #include "../src/llm/http_transport.h"
 #include "../src/llm/py.h"
 #include "agent_memstore.h"
@@ -153,6 +154,7 @@ std::string slurp(const std::string& path) {
 }  // namespace
 
 int main(int argc, char** argv) {
+  agent::DetzTools::set_enabled(false);   // compare the tai.py tool set only
   if (argc < 3) { std::fprintf(stderr, "usage: agent_e2e scenario.json workdir\n"); return 2; }
   Value sc = Value::loads(slurp(argv[1]));
   std::string workdir = argv[2];