vmsig: management daemon, runtime endpoint lifecycle, roster, discovery, in-tree drivers, packaging

- core: runtime attach/detach of a per-endpoint adapter trio (runtime-safe add_adapter + vmsig_core_detach_endpoint, deferred reap)
- roster: VMSIG_EV_ROSTER + CAP_ROSTER, retained per-endpoint and replayed to late subscribers
- discovery: inotify trigger dir, vmid/endpoint slot allocator, host probe; vmsigd daemon with config + per-uid admission
- input driver and vgpu perception built in-tree; vgpu perception as a separate library
- memctx: own the supplied ro_fd (closed at detach)
- deb packaging: install rules, systemd unit, tmpfiles, default config

src/adapter/memctx/memctx.c

@@ -85,7 +85,7 @@ struct vmsig_adapter {
     int           stub;
     const char*   ram_path;       /* armed: RAM-backing path (NOT published outward) */
     uint64_t      low;
-    int           cfg_ro_fd;      /* >=0 => infra-sealed RO-fd (policy); <0 => default */
+    int           cfg_ro_fd;      /* >=0 => infra-sealed RO-fd (owned by adapter, closed in mc_close); <0 => default */
     vmsig_emit    emit;
     int           registered;     /* register_memctx already called                 */
     vmsig_worker* worker;         /* off-loop bootstrap + atomic writes            */
@@ -398,7 +398,11 @@ static void mc_close(vmsig_adapter* a) {
     if (a->win) vmie_win32_close(a->win);   /* AFTER worker join: no in-flight gva_write */
 #endif
     if (a->stub_fd >= 0) close(a->stub_fd);
-    /* cfg_ro_fd belongs to the infrastructure (the open caller) — do NOT close it. */
+    /* ro_fd ownership transferred to the adapter at open(): close it here so a re-grant
+     * (detach + re-attach with a fresh infra ro_fd) does not leak the prior one. Infra
+     * that must keep its own copy dups before handing it in — symmetric to the holder
+     * side, which dups the borrowed RO-fd it receives. */
+    if (a->cfg_ro_fd >= 0) close(a->cfg_ro_fd);
     free(a);
 }