diff --git a/apps/secs_server.cpp b/apps/secs_server.cpp
index 23d8a3f..ee65f66 100644
--- a/apps/secs_server.cpp
+++ b/apps/secs_server.cpp
@@ -766,6 +766,33 @@ int main(int argc, char** argv) {
     return gem::s3f26_carrier_transfer_ack(gem::CarrierActionAck::Accept);
   });
 
+  // S3F19 — Slot Map Verify.  Host sends its expected slot map for
+  // CARRIERID; equipment compares against locally-stored slots and
+  // drives CSMS (NotRead -> Read on Accept, -> Mismatched on Mismatch).
+  router.on(3, 19, [model, logfn](const s2::Message& msg) {
+    auto req = gem::parse_s3f19(msg);
+    if (!req)
+      return gem::s3f20_slot_map_verify_ack(gem::SlotMapVerifyAck::Error);
+    auto* c = model->carriers.get(req->carrierid);
+    if (!c)
+      return gem::s3f20_slot_map_verify_ack(gem::SlotMapVerifyAck::CarrierUnknown);
+    bool match = c->slots.size() == req->slots.size();
+    if (match) {
+      for (std::size_t i = 0; i < req->slots.size(); ++i) {
+        if (static_cast<uint8_t>(c->slots[i].state) !=
+            static_cast<uint8_t>(req->slots[i])) { match = false; break; }
+      }
+    }
+    if (match) {
+      model->carriers.fire_slot_map_event(req->carrierid, gem::SlotMapEvent::Read);
+      logfn("S3F19 CARRIER=" + req->carrierid + " -> S3F20 Accept");
+      return gem::s3f20_slot_map_verify_ack(gem::SlotMapVerifyAck::Accept);
+    }
+    model->carriers.fire_slot_map_event(req->carrierid, gem::SlotMapEvent::Mismatch);
+    logfn("S3F19 CARRIER=" + req->carrierid + " -> S3F20 Mismatch");
+    return gem::s3f20_slot_map_verify_ack(gem::SlotMapVerifyAck::Mismatch);
+  });
+
   // S3F27 — Cancel Carrier (single-EXID form).
   router.on(3, 27, [model, logfn](const s2::Message& msg) {
     auto cid = gem::parse_s3f27(msg);
diff --git a/data/messages.yaml b/data/messages.yaml
index 5ac1dc0..4fbba27 100644
--- a/data/messages.yaml
+++ b/data/messages.yaml
@@ -1335,6 +1335,53 @@ messages:
     builder: s3f26_carrier_transfer_ack
     body: {kind: scalar, item_type: BINARY_BYTE, enum: CarrierActionAck, param: caack}
 
+  # S3F19 / S3F20 — Slot Map Verify.  Host sends its expected slot map
+  # for the carrier; equipment compares against its locally-read map
+  # and replies SVACK (Accept/Mismatch).  On Accept, CSMS transitions
+  # to Read; on Mismatch, CSMS goes to Mismatched.
+  - id: S3F19
+    stream: 3
+    function: 19
+    w: true
+    builder: s3f19_slot_map_verify
+    parser: parse_s3f19
+    body:
+      kind: list
+      struct_name: SlotMapVerifyRequest
+      fields:
+        - {name: carrierid, shape: {kind: scalar, item_type: ASCII}}
+        - name: slots
+          shape: {kind: list_of, element: {kind: scalar, item_type: BINARY_BYTE}}
+
+  - id: S3F20
+    stream: 3
+    function: 20
+    builder: s3f20_slot_map_verify_ack
+    body: {kind: scalar, item_type: BINARY_BYTE, enum: SlotMapVerifyAck, param: svack}
+
+  # S3F21 / S3F22 — Slot Map Report.  Equipment-initiated report of
+  # the slot map it sees (typically pushed after a CARRIERID is read
+  # so the host can decide whether to ProceedWithCarrier).
+  - id: S3F21
+    stream: 3
+    function: 21
+    w: true
+    builder: s3f21_slot_map_report
+    parser: parse_s3f21
+    body:
+      kind: list
+      struct_name: SlotMapReport
+      fields:
+        - {name: carrierid, shape: {kind: scalar, item_type: ASCII}}
+        - name: slots
+          shape: {kind: list_of, element: {kind: scalar, item_type: BINARY_BYTE}}
+
+  - id: S3F22
+    stream: 3
+    function: 22
+    builder: s3f22_slot_map_report_ack
+    body: {kind: scalar, item_type: BINARY_BYTE, enum: SlotMapVerifyAck, param: svack}
+
   # S3F27 / S3F28 — Cancel Carrier (host cancels a carrier operation).
   - id: S3F27
     stream: 3
diff --git a/include/secsgem/gem/messages_helpers.hpp b/include/secsgem/gem/messages_helpers.hpp
index 266a96f..245943f 100644
--- a/include/secsgem/gem/messages_helpers.hpp
+++ b/include/secsgem/gem/messages_helpers.hpp
@@ -189,4 +189,13 @@ enum class PortGroupAck : uint8_t {
   Error  = 1,
 };
 
+// E87 slot-map verify ack code (SVACK).  Same byte used by S3F20
+// (verify reply) and S3F22 (host's ack of equipment's slot-map report).
+enum class SlotMapVerifyAck : uint8_t {
+  Accept       = 0,
+  Mismatch     = 1,
+  CarrierUnknown = 2,
+  Error        = 3,
+};
+
 }  // namespace secsgem::gem
diff --git a/tests/test_messages.cpp b/tests/test_messages.cpp
index e04dd30..879bf0e 100644
--- a/tests/test_messages.cpp
+++ b/tests/test_messages.cpp
@@ -782,6 +782,34 @@ TEST_CASE("S3F25 / S3F26 CarrierTransfer round-trip") {
   CHECK(*ack_byte(s3f26_carrier_transfer_ack(CarrierActionAck::Accept)) == 0);
 }
 
+TEST_CASE("S3F19 / S3F20 SlotMapVerify round-trip") {
+  std::vector<std::string> raw_slots = {std::string({0x01, 0x01, 0x00, 0x01})};
+  // Build via the typed builder: list of BINARY_BYTE per slot.
+  std::vector<uint8_t> slots = {0x01, 0x01, 0x00, 0x01};
+  auto m = s3f19_slot_map_verify("CAR-001", slots);
+  CHECK(m.stream == 3);
+  CHECK(m.function == 19);
+  CHECK(m.reply_expected);
+
+  auto parsed = parse_s3f19(m);
+  REQUIRE(parsed.has_value());
+  CHECK(parsed->carrierid == "CAR-001");
+  CHECK(parsed->slots == slots);
+
+  CHECK(*ack_byte(s3f20_slot_map_verify_ack(SlotMapVerifyAck::Accept))   == 0);
+  CHECK(*ack_byte(s3f20_slot_map_verify_ack(SlotMapVerifyAck::Mismatch)) == 1);
+}
+
+TEST_CASE("S3F21 / S3F22 SlotMapReport round-trip") {
+  std::vector<uint8_t> slots = {0x01, 0x00};
+  auto m = s3f21_slot_map_report("CAR-002", slots);
+  auto parsed = parse_s3f21(m);
+  REQUIRE(parsed.has_value());
+  CHECK(parsed->carrierid == "CAR-002");
+  CHECK(parsed->slots == slots);
+  CHECK(*ack_byte(s3f22_slot_map_report_ack(SlotMapVerifyAck::Accept)) == 0);
+}
+
 TEST_CASE("S3F27 / S3F28 CancelCarrier round-trip") {
   auto m = s3f27_cancel_carrier("CAR-001");
   auto parsed = parse_s3f27(m);