C3: AlarmSeverity bit-flag enum + classification helpers

ALCD's lower 7 bits are a bitmap of category flags per E5 §10.3 and
E30 §6.13; a single alarm may carry multiple categories at once
(e.g. an irrecoverable equipment-safety fault is 0x10 | 0x02).
Adds:

  enum class AlarmSeverity : uint8_t
    PersonalSafety  EquipmentSafety  ParameterError  ParameterWarning
    Irrecoverable   EquipmentStatus  Attention

  has_severity(alcd, bit), severity_bits(alcd)
  Alarm::has(bit), Alarm::is_safety()
  constexpr severity_mask = 0x7F

Tests cover single-category alarms, multi-category combos, and that
the bit-7 SET/CLEAR flag is correctly excluded from category bits.

Closes Tranche C (E5 alarm/exception state model).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

include/secsgem/gem/store/alarms.hpp

@@ -10,13 +10,40 @@
 
 namespace secsgem::gem {
 
+// ALCD bit-flag categories (E5 §10.3 / E30 §6.13).  The lower 7 bits
+// of ALCD are a bitmap — an alarm may carry multiple categories at
+// once (e.g. an irrecoverable equipment-safety fault is 0x10 | 0x02).
+// Bit 7 is the alarm SET/CLEAR flag, applied at emit time and not
+// part of the category bitmap.
+enum class AlarmSeverity : uint8_t {
+  PersonalSafety      = 0x01,
+  EquipmentSafety     = 0x02,
+  ParameterError      = 0x04,  // parameter control error
+  ParameterWarning    = 0x08,  // parameter control warning
+  Irrecoverable       = 0x10,
+  EquipmentStatus     = 0x20,  // equipment status warning
+  Attention           = 0x40,  // attention flag (lowest-priority)
+};
+
+inline constexpr uint8_t severity_mask = 0x7F;
+
+inline bool has_severity(uint8_t alcd, AlarmSeverity bit) {
+  return (alcd & static_cast<uint8_t>(bit)) != 0;
+}
+
+inline uint8_t severity_bits(uint8_t alcd) { return alcd & severity_mask; }
+
 struct Alarm {
   uint32_t id;
   std::string text;
-  // Lower 7 bits of ALCD: severity category (1=personal safety,
+  // Lower 7 bits of ALCD: severity bitmap (see AlarmSeverity).  Bit 7
-  // 2=equipment safety, 4=parameter control error, ...).  Bit 7 marks
+  // marks set vs cleared and is applied at emit time.
-  // set vs cleared and is applied at emit time.
   uint8_t severity_category;
+
+  bool has(AlarmSeverity bit) const { return has_severity(severity_category, bit); }
+  bool is_safety() const {
+    return has(AlarmSeverity::PersonalSafety) || has(AlarmSeverity::EquipmentSafety);
+  }
 };
 
 enum class AlarmAck : uint8_t {

tests/test_data_model.cpp

@@ -169,6 +169,34 @@ TEST_CASE("alarm enable / set / clear / list") {
   CHECK(r.all().size() == 2);
 }
 
+TEST_CASE("AlarmSeverity bit-flag helpers (E5 §10.3 / E30 §6.13)") {
+  // Single-category alarms.
+  Alarm safety{1, "door open", static_cast<uint8_t>(AlarmSeverity::PersonalSafety)};
+  CHECK(safety.has(AlarmSeverity::PersonalSafety));
+  CHECK_FALSE(safety.has(AlarmSeverity::EquipmentSafety));
+  CHECK(safety.is_safety());
+
+  Alarm temp_warn{2, "chiller high",
+                  static_cast<uint8_t>(AlarmSeverity::ParameterWarning)};
+  CHECK_FALSE(temp_warn.is_safety());
+  CHECK(temp_warn.has(AlarmSeverity::ParameterWarning));
+
+  // Multi-category alarms: combine Irrecoverable + EquipmentSafety.
+  Alarm combo{3, "spindle seized",
+              static_cast<uint8_t>(
+                  static_cast<uint8_t>(AlarmSeverity::EquipmentSafety) |
+                  static_cast<uint8_t>(AlarmSeverity::Irrecoverable))};
+  CHECK(combo.is_safety());
+  CHECK(combo.has(AlarmSeverity::Irrecoverable));
+  CHECK(combo.has(AlarmSeverity::EquipmentSafety));
+  CHECK_FALSE(combo.has(AlarmSeverity::PersonalSafety));
+
+  // The ALCD set-bit is *not* part of the category bitmap.
+  const uint8_t set_alcd = static_cast<uint8_t>(combo.severity_category | 0x80);
+  CHECK(severity_bits(set_alcd) == combo.severity_category);
+  CHECK(has_severity(set_alcd, AlarmSeverity::Irrecoverable));
+}
+
 // ---- Process programs ----------------------------------------------------
 
 TEST_CASE("recipe CRUD") {