feat: EquipmentRuntime engine owner + secs_gemd gRPC daemon

Extract the SECS/GEM engine wiring out of the secs_server app into a
reusable class, and stand up a language-agnostic gRPC daemon on top so a
tool's software (any language) can drive the equipment without linking C++
or knowing SEMI. Foundation for replacing a vendor's SECS/GEM server.

Engine reuse:
- EquipmentRuntime (include/secsgem/gem/runtime.hpp, src/gem/runtime.cpp):
  owns io_context, passive Server, model, control-state machine, Router;
  thread-safe outbound API (set_variable/emit_event/set_alarm/clear_alarm),
  on_command hook, deliver_or_spool, run()/run_async()/poll()/stop().
- register_default_handlers (src/gem/default_handlers.cpp): the 56 GEM
  handlers + domain emitters, relocated from secs_server so the app and the
  daemon speak byte-identical GEM. secs_server.cpp reduced ~1270 -> 113 lines.
- name_index.hpp: resolve_variable(name) -> VID (the name->id binding layer).

Daemon (apps/secs_gemd.cpp, proto/secsgem/v1/equipment.proto):
- runs the engine + HSMS link on a background thread; serves the gRPC
  Equipment service. Increment 1: SetVariables (name-resolved, plain
  value->Item) and GetControlState. proto carries the full v1 surface
  (universal + carrier/recipe/job tiers); remaining RPCs + the Subscribe
  command stream are next (docs/DAEMON_ROADMAP.md).
- CMake: opt-in SECSGEM_DAEMON, protoc/grpc_cpp_plugin codegen, gracefully
  skipped where protobuf/grpc++ are absent. Dockerfile gains the grpc deps.

Tests (proof): test_runtime, test_default_handlers (S1F1->S1F2, S2F41->hook),
test_name_index. Full suite 458/458, 2795 assertions; live server<->client
GEM300 demo still passes on the refactored server.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_runtime.cpp

@@ -0,0 +1,66 @@
+#include <doctest/doctest.h>
+
+#include <vector>
+
+#include "secsgem/gem/runtime.hpp"
+#include "secsgem/secs2/item.hpp"
+
+using namespace secsgem;
+namespace gem = secsgem::gem;
+namespace s2  = secsgem::secs2;
+
+#ifndef SECSGEM_DATA_DIR
+#error "SECSGEM_DATA_DIR not defined; see CMakeLists.txt"
+#endif
+
+// Port 0 binds an OS-chosen ephemeral port. These tests never call run()/
+// run_async(), so the acceptor is opened but never armed — we exercise the
+// outbound API by posting and draining with poll(), no host involved.
+static gem::EquipmentRuntime::Config test_config() {
+  gem::EquipmentRuntime::Config c;
+  c.equipment_yaml     = SECSGEM_DATA_DIR "/equipment.yaml";
+  c.control_state_yaml = SECSGEM_DATA_DIR "/control_state.yaml";
+  c.process_job_yaml   = SECSGEM_DATA_DIR "/process_job_state.yaml";
+  c.control_job_yaml   = SECSGEM_DATA_DIR "/control_job_state.yaml";
+  c.port = 0;
+  return c;
+}
+
+TEST_CASE("EquipmentRuntime loads the data dictionary from config") {
+  gem::EquipmentRuntime rt(test_config());
+  CHECK(rt.model().svids.all().size() == 3);
+  CHECK(rt.model().alarms.all().size() == 2);
+  CHECK(rt.control_state() == gem::ControlState::HostOffline);
+}
+
+TEST_CASE("EquipmentRuntime.set_variable posts onto the io thread and updates the model") {
+  gem::EquipmentRuntime rt(test_config());
+  rt.set_variable(1, s2::Item::ascii("OnlineRemote"));
+  CHECK(rt.model().svids.value(1) != s2::Item::ascii("OnlineRemote"));  // not yet — posted
+  rt.poll();
+  CHECK(rt.model().svids.value(1) == s2::Item::ascii("OnlineRemote"));
+}
+
+TEST_CASE("EquipmentRuntime.set_alarm / clear_alarm toggle the active flag") {
+  gem::EquipmentRuntime rt(test_config());
+  rt.set_alarm(1);
+  rt.poll();
+  CHECK(rt.model().alarms.active(1));
+  rt.clear_alarm(1);
+  rt.poll();
+  CHECK_FALSE(rt.model().alarms.active(1));
+}
+
+TEST_CASE("EquipmentRuntime.on_command registers the behaviour hook on the model") {
+  gem::EquipmentRuntime rt(test_config());
+  bool ran = false;
+  rt.on_command("START", [&](const std::string& rcmd,
+                             const std::vector<gem::CommandParameter>&) {
+    ran = (rcmd == "START");
+    return gem::HostCmdAck::Accept;
+  });
+  CHECK(rt.model().commands.has_handler("START"));
+  auto res = rt.model().commands.dispatch("START", {});
+  CHECK(ran);
+  CHECK(res.ack == gem::HostCmdAck::Accept);
+}