stcp: ed25519 pubkey exchange in handshake, fix instance destroy segfault, fix chat_tcp_test

- u_async.c: process immediate_queue BEFORE epoll_wait in uasync_poll
- stcp_link.c: defensive NULL etcp_conn/etcp_link in stcp_link_close
- utun_instance.c: move stcp_server_list_destroy_all to Phase J (before ETCP),
  add deferred drain in both Phase J and L
- stcp.h/c: STCP_HS_ENC_CLIENT 6→38, STCP_HS_ENC_SERVER 7→39,
  exchange ed25519_pubkey in both handshake directions
- etcp_connections.c: copy peer_ed25519 from STCP to ETCP_CONN in
  etcp_link_enter_ready_tcp; guard link->etcp in tcp_link_close_cb
- chat_sync.c: fix lk->conn NULL dereference for TCP links
- test_stcp.c: update stcp_server_create/stcp_client_connect callsites
- tools/chat_tcp_test: change transport udp→tcp

malloc_test.c

@@ -0,0 +1,52 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#define BLOCK_SIZE 10
+
+static int counts[] = {0, 100, 1000, 10000, 100000};
+static int n_counts = 5;
+
+static long read_vm_field(const char *field) {
+    char path[64], buf[256];
+    snprintf(path, sizeof(path), "/proc/%d/status", getpid());
+    FILE *f = fopen(path, "r");
+    if (!f) return -1;
+    long val = -1;
+    while (fgets(buf, sizeof(buf), f)) {
+        if (strncmp(buf, field, strlen(field)) == 0) {
+            sscanf(buf + strlen(field) + 1, "%ld", &val);
+            break;
+        }
+    }
+    fclose(f);
+    return val;
+}
+
+static void measure(const char *label) {
+    long rss = read_vm_field("VmRSS");
+    long data = read_vm_field("VmData");
+    long size = read_vm_field("VmSize");
+    printf("  %-8s  VmRSS=%6ld kB  VmData=%6ld kB  VmSize=%6ld kB\n", label, rss, data, size);
+}
+
+int main(void) {
+    printf("Block size: %d bytes\n", BLOCK_SIZE);
+
+    for (int c = 0; c < n_counts; c++) {
+        int n = counts[c];
+        printf("\n--- %d blocks (requested %d bytes) ---\n", n, n * BLOCK_SIZE);
+        measure("before");
+
+        void **ptrs = malloc(n * sizeof(void*));
+        for (int i = 0; i < n; i++) {
+            ptrs[i] = malloc(BLOCK_SIZE);
+            memset(ptrs[i], 0, BLOCK_SIZE);
+        }
+
+        measure("after ");
+        free(ptrs);
+    }
+    return 0;
+}