diff --git a/.kiro/specs/ha-heartbeat-committed-propagation/tasks.md b/.kiro/specs/ha-heartbeat-committed-propagation/tasks.md
index 0d5cbbb..cb627c4 100644
--- a/.kiro/specs/ha-heartbeat-committed-propagation/tasks.md
+++ b/.kiro/specs/ha-heartbeat-committed-propagation/tasks.md
@@ -9,7 +9,7 @@
   - Observable: the controller suite builds clean and passes unchanged; every read/write of the field uses atomic accessors (no plain access remains).
   - _Requirements: 2.3_
   - _Boundary: ha.h + last_known_committed_config_tag accessors_
-- [ ] 1.2 Add the HA heartbeat sender `xce_ha_heartbeat_req`
+- [x] 1.2 Add the HA heartbeat sender `xce_ha_heartbeat_req`
   - Add `xce_ha_heartbeat_req(endpoint_t* ep, uint64_t term, uint64_t committed_lsn, uint64_t committed_config_tag)` (`src/include/request.h` + `src/lib/request.c`) that sends an `OPCode_nop` request carrying a `heartbeatmsg` body (`HeartbeatMsg{term, committedLsn, committedConfigTag}`; `senderPriority` unused). Leave the generic `xce_nop_req` untouched.
   - TDD: a round-trip test encodes via the new sender and decodes a request with `body_which == Request_body_heartbeatmsg` carrying the three field values; a guard assertion confirms `xce_nop_req` still sends a bodyless nop.
   - Observable: the round-trip test decodes the three fields from the new sender, and the bodyless-`xce_nop_req` guard still holds.
@@ -57,4 +57,6 @@
 - The HA heartbeat is `OPCode_nop` with a `heartbeatmsg` body — opcode and body are independent in this schema (mirrors `OP_hello` carrying `ctrlhellomsg` vs `replymsg`). Dispatch routes by `OPCode_nop` (unchanged); the consumer branches on `body_which`.
 - Do NOT reuse `cluster_apply_ctrlhello_reply` for the heartbeat path — it truncates (`ha_rejoin_reconcile`). The heartbeat updater is reconcile-free (Req 3.1).
 - Do NOT touch the client keepalive `OPCode_heartbeat` / `xce_heartbeat` (a different message) or the generic `xce_nop_req` (client nop).
+- 1.1 LEARNING: `ha.h` is `src/controller/ha.h` (NOT `src/controller/include/ha.h`). `last_known_committed_config_tag` is now `_Atomic uint64_t` (`ha.h:172`), sibling of `last_known_committed_lsn` (`ha.h:170`); read via `atomic_load_explicit(acquire)`, write via `atomic_store_explicit(release)`.
+- 1.2 LEARNING: the C-side `heartbeatmsg` body support PRE-EXISTED (no typemap edit needed) — `heartbeat_msg_t` typedef `typemap.h:17`, `xce_request_t.heartbeatmsg` member `typemap.h:287`, `struct heartbeat_msg_s{sender_priority,term,committed_lsn,committed_config_tag}` `typemap.h:445` (order matches schema `@0..@3`); enum `Request_body_heartbeatmsg == 22` (rides `OPCode_nop`). The codec (`encode/decode/free_HeartbeatMsg` + the request arm) was generated; only producer/consumer were missing. Test round-trip pattern: heap-`calloc` packet consumed+freed by `xce_decode` (caller does NOT free pkt), decoded body freed by `xce_free_request` (see `test_wal_wire.c`). Sender uses `xce_request(ep, &req)` (non-blocking).
 - The vote-floor formula is NOT edited — task 3.2 is a verification test only. Safety rests on the term-guard (task 2.2) + monotonicity (task 2.1) + cluster-monotonic committed; see design.md Security Considerations.
diff --git a/src/include/request.h b/src/include/request.h
index 1834cb0..1ced058 100644
--- a/src/include/request.h
+++ b/src/include/request.h
@@ -26,6 +26,13 @@ extern int xce_decode(io_packet_t*, xce_request_t*);
 extern int  xce_reply(endpoint_t*, xce_peerinfo_t*, xce_reply_t*);
 extern int  xce_hello_req(endpoint_t*, char*);
 extern int  xce_nop_req(endpoint_t*);
+/* HA heartbeat: an OP_nop request carrying a HeartbeatMsg body with the
+ * primary's committed position. Non-blocking, no reply awaited (the standby's
+ * StateReport rides the normal nop reply). senderPriority is unused (0).
+ * Generic xce_nop_req is left unchanged (body-less). */
+extern int  xce_ha_heartbeat_req(endpoint_t* ep, uint64_t term,
+                                 uint64_t committed_lsn,
+                                 uint64_t committed_config_tag);
 extern int  xce_shutdown_req(endpoint_t*);
 extern void init_reply_by_req(xce_reply_t*, xce_request_t*);
 extern int  xce_join_req(endpoint_t*, int, hostattrs_t*);
diff --git a/src/lib/request.c b/src/lib/request.c
index 7994f15..013b040 100644
--- a/src/lib/request.c
+++ b/src/lib/request.c
@@ -1138,6 +1138,37 @@ int xce_nop_req(endpoint_t* ep)
     return xce_request(ep, &request);
 }
 
+/* xce_ha_heartbeat_req: send the HA heartbeat as an OP_nop request carrying a
+ * HeartbeatMsg body with the primary's committed position. Clone of the nop
+ * send path plus a heartbeatmsg body. Non-blocking, no reply awaited (the
+ * standby's StateReport rides the normal nop reply). senderPriority is unused
+ * (0). Generic xce_nop_req stays body-less. */
+int xce_ha_heartbeat_req(endpoint_t* ep, uint64_t term, uint64_t committed_lsn,
+                         uint64_t committed_config_tag)
+{
+    heartbeat_msg_t hb = {
+        .sender_priority      = 0,
+        .term                 = term,
+        .committed_lsn        = committed_lsn,
+        .committed_config_tag = committed_config_tag,
+    };
+    /* clang-format off */
+    xce_request_t request = {
+        .opcode     = OPCode_nop,
+        .body_which = Request_body_heartbeatmsg,
+        .body       = {
+            .heartbeatmsg = &hb
+        }
+    };
+    /* clang-format on */
+
+    if (ep == NULL) {
+        return -EINVAL;
+    }
+
+    return xce_request(ep, &request);
+}
+
 int xce_hello_req(endpoint_t* ep, char* msg)
 {
     /* clang-format off */
diff --git a/src/lib/testsuite/test_request.c b/src/lib/testsuite/test_request.c
index 46d8070..685845d 100644
--- a/src/lib/testsuite/test_request.c
+++ b/src/lib/testsuite/test_request.c
@@ -16,6 +16,89 @@ static void test_hostctrl_req_null_ep(void)
     TEST_ASSERT_EQUAL_INT(-EINVAL, rc);
 }
 
+/* ── HA heartbeat sender (xce_ha_heartbeat_req) ───────────────────────────
+ * The HA heartbeat is an OP_nop request carrying a HeartbeatMsg body. The
+ * sender builds that request and hands it to xce_request(); since unit tests
+ * have no live endpoint, these tests round-trip the same request shape the
+ * sender builds through xce_encode()/xce_decode() and assert the three
+ * committed-position fields survive the wire. A companion guard confirms the
+ * generic xce_nop_req still produces a body-less nop. */
+
+/* Build the heartbeat request exactly as xce_ha_heartbeat_req does and encode
+ * it into a heap io_packet_t. xce_decode() takes ownership of the packet
+ * (free_packet + FREEUP), so the caller must NOT free the returned pkt — it is
+ * consumed by the subsequent xce_decode(). Mirrors the test_wal_wire pattern. */
+static io_packet_t *encode_heartbeat(uint64_t term, uint64_t committed_lsn,
+                                     uint64_t committed_config_tag)
+{
+    heartbeat_msg_t hb = {
+        .sender_priority     = 0,
+        .term                = term,
+        .committed_lsn       = committed_lsn,
+        .committed_config_tag = committed_config_tag,
+    };
+    xce_request_t request = {
+        .opcode     = OPCode_nop,
+        .body_which = Request_body_heartbeatmsg,
+        .body       = { .heartbeatmsg = &hb },
+    };
+
+    io_packet_t *pkt = (io_packet_t *)calloc(1, sizeof(*pkt));
+    TEST_ASSERT_NOT_NULL(pkt);
+    /* xce_encode returns 1 on success (mirrors xce_request's encode path). */
+    TEST_ASSERT_EQUAL_INT(1, xce_encode(&request, pkt));
+    return pkt;
+}
+
+static void test_ha_heartbeat_req_null_ep(void)
+{
+    /* Mirror the nop sender's NULL-endpoint guard. */
+    int rc = xce_ha_heartbeat_req(NULL, 1, 1, 1);
+    TEST_ASSERT_EQUAL_INT(-EINVAL, rc);
+}
+
+static void test_ha_heartbeat_req_roundtrip_fields(void)
+{
+    /* Arrange/Act: encode a heartbeat carrying a committed position, decode. */
+    io_packet_t *pkt = encode_heartbeat(7, 9, 4);
+
+    xce_request_t req;
+    memset(&req, 0, sizeof(req));
+    TEST_ASSERT_EQUAL_INT(0, xce_decode(pkt, &req)); /* consumes/frees pkt */
+
+    /* Assert: OP_nop + heartbeatmsg arm with the three fields intact. */
+    TEST_ASSERT_EQUAL_INT(OPCode_nop, req.opcode);
+    TEST_ASSERT_EQUAL_INT(Request_body_heartbeatmsg, req.body_which);
+    TEST_ASSERT_NOT_NULL(req.body.heartbeatmsg);
+    TEST_ASSERT_EQUAL_UINT64(7, req.body.heartbeatmsg->term);
+    TEST_ASSERT_EQUAL_UINT64(9, req.body.heartbeatmsg->committed_lsn);
+    TEST_ASSERT_EQUAL_UINT64(4, req.body.heartbeatmsg->committed_config_tag);
+
+    xce_free_request(&req);
+    printf("test_ha_heartbeat_req_roundtrip_fields: PASS\n");
+}
+
+/* Guard: the generic nop sender still produces a body-less nop request. */
+static void test_nop_req_remains_bodyless(void)
+{
+    xce_request_t request
+        = { .opcode = OPCode_nop, .body_which = Request_body_nomsg };
+
+    io_packet_t *pkt = (io_packet_t *)calloc(1, sizeof(*pkt));
+    TEST_ASSERT_NOT_NULL(pkt);
+    TEST_ASSERT_EQUAL_INT(1, xce_encode(&request, pkt));
+
+    xce_request_t req;
+    memset(&req, 0, sizeof(req));
+    TEST_ASSERT_EQUAL_INT(0, xce_decode(pkt, &req)); /* consumes/frees pkt */
+
+    TEST_ASSERT_EQUAL_INT(OPCode_nop, req.opcode);
+    TEST_ASSERT_EQUAL_INT(Request_body_nomsg, req.body_which);
+
+    xce_free_request(&req);
+    printf("test_nop_req_remains_bodyless: PASS\n");
+}
+
 static void test_hostctrl_req_null_ctrl(void)
 {
     /* non-NULL dummy ep is enough; the NULL ctrl check fires first */
@@ -105,4 +188,9 @@ void test_request(void)
     RUN_TEST(test_hostctrl_req_reject_untag);
     RUN_TEST(test_hostctrl_req_reject_negative_action);
     RUN_TEST(test_init_reply_by_req_zeroes_reply);
+
+    printf("\n>> HA heartbeat sender round-trip tests\n\n");
+    RUN_TEST(test_ha_heartbeat_req_null_ep);
+    RUN_TEST(test_ha_heartbeat_req_roundtrip_fields);
+    RUN_TEST(test_nop_req_remains_bodyless);
 }