feat: add ha.h stub + ha.c skeleton; document iomgr/SSL reuse decision (P1-1)

src/controller/ha.c

@@ -0,0 +1,3 @@
+#include "ha.h"
+
+/* P1-2: implementation added in next task */

src/controller/ha.h

@@ -0,0 +1,18 @@
+#ifndef HA_H
+#define HA_H
+
+/*
+ * XCE Controller HA — role management and election (P1).
+ *
+ * P1-1 audit: the existing create_ssl_context() + iomgr_set_ssl_ctx() path
+ * in cluster.c (line 559, set at line 583) covers all controller-to-controller SSL.
+ * HA listeners (heartbeat, election probe, replication accept) reuse the same
+ * ssl_ctx already installed on c->iomgr.
+ * No new TLS infrastructure is needed — XCE runs on a trusted management LAN.
+ * Peer identity is validated by host:port match against the --peers candidate list.
+ * See design doc Part 5.9 and memory: Persistence & HA Trusted LAN Decision.
+ */
+
+/* Full struct definitions and API declarations added in P1-2. */
+
+#endif /* HA_H */

src/controller/meson.build

@@ -1,6 +1,7 @@
 controller_src = [
   'cluster.c',
   'dataex.c',
+  'ha.c',
   'job.c',
   'join.c',
   'main.c',