feat(daemon): Phase D — GEM300 in-the-loop (jobs, recipes, EC changes)

Semantics settled and documented: v1 is observe-and-report. The engine keeps
acking S16/S3/S7/S2F15 from its FSM tables — exactly the behaviour both
reference implementations validated — while the tool observes lifecycle
events on the Subscribe stream and reports physical progress back. Gating
stays the documented v2 deferred-reply item.

Engine: two new store observers (HandlerSlot pattern) — RecipeStore fires
(ppid, body) after an add (S7F3 downloads), EquipmentConstantStore fires
(id, value) on ACCEPTED S2F15 writes only. Unit-tested.

Daemon: the service registers PJ/recipe/EC observers (io thread; add_
observers coexist with register_default_handlers' primaries) and fans the
new HostRequest variants out via push_request (fire-and-forget, no-
buffering contract). ProcessJob carries action (Start->START, Resume->
RESUME, Paused->PAUSE, Stopping->STOP, Aborting->ABORT) + recipe + material
bindings read store-side on the io thread. ReportProcessJob maps SETTING_UP
->SetupComplete, COMPLETE->ProcessComplete, ABORTED->AbortComplete via
read_sync; PROCESSING is informational; unknown job => INVALID_OBJECT,
table-rejected transition => CANNOT_DO_NOW. Carriers deferred (CarrierStore
has no observer machinery; ReportCarrier stays UNIMPLEMENTED) — roadmap.

Python client: on_process_job / on_recipe / on_constant_change decorators +
report_job(job_id, state); ProcessJob dataclass exported.

Tests: daemon suite 141 -> 175 assertions — the full in-process loop
(S16F11 create -> tool setup -> S16F5 PJSTART -> stream ProcessJob with
recipe+carriers -> ReportProcessJob(COMPLETE) -> FSM at ProcessComplete),
rejection paths, S7F3 -> ProcessProgram, S2F15 -> ConstantChange with the
configured name. Core 475/3097 (observer units). Live regression: daemon
interop 20 checks + pyclient 13 checks still green against the running
daemon.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

include/secsgem/gem/store/equipment_constants.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstdint>
+#include <functional>
 #include <map>
 #include <optional>
 #include <stdexcept>
@@ -9,6 +10,7 @@
 #include <variant>
 #include <vector>
 
+#include "secsgem/gem/handler_slot.hpp"
 #include "secsgem/secs2/item.hpp"
 
 namespace secsgem::gem {
@@ -59,10 +61,18 @@ class EquipmentConstantStore {
     if (it == by_id_.end()) return EquipmentAck::Denied_UnknownEcid;
     if (!in_range(it->second, value)) return EquipmentAck::Denied_OutOfRange;
     it->second.value = std::move(value);
+    if (on_changed_) on_changed_(id, it->second.value);
     return EquipmentAck::Accept;
   }
 
+  // Observe ACCEPTED host writes (S2F15): fires after the value is stored.
+  // The tool reacts to process-parameter tuning; rejected writes don't fire.
+  using ChangedHandler = std::function<void(uint32_t, const s2::Item&)>;
+  void add_changed_handler(ChangedHandler h) { on_changed_.add(std::move(h)); }
+
  private:
+  HandlerSlot<uint32_t, const s2::Item&> on_changed_;
+
   // For numeric formats, parse min_str / max_str as integers / doubles and
   // compare against the first value of the array (we don't support setting
   // multi-element ECs in this implementation).