OpenCode-style TUI, model probing, sandboxed auto approval

- TUI: centered home screen with logo, boxed input with mode line, sidebar
  (>=120 cols), Ctrl+P palette, Tab Build/Plan, Shift+Tab approval cycle,
  mouse (cards, cursor, pickers, wheel), /sidebar /mouse /approval
- /models probing: key check on entry (401 re-asks), API models in /model
- Shell sandbox in C: Linux Landlock (writes limited to workspace/tmp,
  ABI>=4 blocks TCP), macOS sandbox_init, rules fallback elsewhere
- Approval modes ask/auto/yolo (default auto); read-only command whitelist;
  ask to rerun outside the sandbox when a command looks blocked
- Upgradable bootstrap scripts (git pull --ff-only, rebuild, reinstall) and
  cst-agent-update; cst-agent --version
- tests: test_sandbox, test_models

tests/test_models.c

@@ -0,0 +1,130 @@
+#ifndef _DEFAULT_SOURCE
+#define _DEFAULT_SOURCE
+#endif
+
+#include "cst_agent.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifdef _WIN32
+int main(void) {
+  puts("test_models: skipped on Windows");
+  return 0;
+}
+#else
+
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <pthread.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#define CHECK(c)                                                               \
+  do {                                                                         \
+    if (!(c)) {                                                                \
+      fprintf(stderr, "%s:%d: CHECK(%s) failed\n", __FILE__, __LINE__, #c);   \
+      exit(1);                                                                 \
+    }                                                                          \
+  } while (0)
+
+/* One canned HTTP response per accepted connection. */
+static const char *g_responses[8];
+static int g_nresp;
+static int g_listen = -1;
+static char g_request[4096];
+
+static void *serve(void *arg) {
+  (void)arg;
+  for (int i = 0; i < g_nresp; i++) {
+    int c = accept(g_listen, NULL, NULL);
+    if (c < 0)
+      return NULL;
+    ssize_t n = recv(c, g_request, sizeof(g_request) - 1, 0);
+    g_request[n > 0 ? n : 0] = 0;
+    const char *r = g_responses[i];
+    ssize_t off = 0, len = (ssize_t)strlen(r);
+    while (off < len) {
+      ssize_t w = send(c, r + off, (size_t)(len - off), 0);
+      if (w <= 0)
+        break;
+      off += w;
+    }
+    close(c);
+  }
+  return NULL;
+}
+
+static int start_server(void) {
+  g_listen = socket(AF_INET, SOCK_STREAM, 0);
+  CHECK(g_listen >= 0);
+  int one = 1;
+  setsockopt(g_listen, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
+  struct sockaddr_in a;
+  memset(&a, 0, sizeof(a));
+  a.sin_family = AF_INET;
+  a.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+  CHECK(bind(g_listen, (struct sockaddr *)&a, sizeof(a)) == 0);
+  CHECK(listen(g_listen, 8) == 0);
+  socklen_t al = sizeof(a);
+  CHECK(getsockname(g_listen, (struct sockaddr *)&a, &al) == 0);
+  return ntohs(a.sin_port);
+}
+
+#define RESP(status, body)                                                     \
+  "HTTP/1.1 " status "\r\nContent-Type: application/json\r\n"                  \
+  "Connection: close\r\n\r\n" body
+
+int main(void) {
+  g_responses[0] = RESP("200 OK", "{\"object\":\"list\",\"data\":["
+                                  "{\"id\":\"deepseek-flash\"},"
+                                  "{\"id\":\"deepseek-v4-pro\"},"
+                                  "{\"id\":\"deepseek-flash\"}]}");
+  g_responses[1] = RESP("401 Unauthorized", "{\"error\":\"bad key\"}");
+  g_responses[2] = RESP("200 OK", "<html>not json</html>");
+  g_responses[3] = RESP("200 OK", "{\"models\":[{\"name\":\"m1\"},"
+                                  "{\"name\":\"m2\"}]}");
+  g_responses[4] = RESP("500 Internal Server Error", "{}");
+  g_nresp = 5;
+  int port = start_server();
+  pthread_t th;
+  CHECK(pthread_create(&th, NULL, serve, NULL) == 0);
+
+  char base[64];
+  snprintf(base, sizeof(base), "http://127.0.0.1:%d/v1/", port);
+  char ids[8][128], err[256];
+
+  /* data[].id, duplicates folded, trailing slash on the base */
+  int n = cst_llm_list_models(base, "sk-test", ids, 8, err, sizeof(err));
+  CHECK(n == 2);
+  CHECK(strcmp(ids[0], "deepseek-flash") == 0);
+  CHECK(strcmp(ids[1], "deepseek-v4-pro") == 0);
+  CHECK(strncmp(g_request, "GET /v1/models ", 15) == 0);
+  CHECK(strstr(g_request, "Authorization: Bearer sk-test") != NULL);
+
+  n = cst_llm_list_models(base, "sk-bad", ids, 8, err, sizeof(err));
+  CHECK(n == CST_MODELS_AUTH);
+  CHECK(strstr(err, "401") != NULL);
+
+  n = cst_llm_list_models(base, "sk-test", ids, 8, err, sizeof(err));
+  CHECK(n == -1);
+  CHECK(err[0]);
+
+  n = cst_llm_list_models(base, "sk-test", ids, 8, err, sizeof(err));
+  CHECK(n == 2 && strcmp(ids[1], "m2") == 0);
+
+  n = cst_llm_list_models(base, "sk-test", ids, 8, err, sizeof(err));
+  CHECK(n == -1 && strstr(err, "500") != NULL);
+
+  pthread_join(th, NULL);
+  close(g_listen);
+
+  /* nothing listening: network error, not an auth failure */
+  n = cst_llm_list_models(base, "sk-test", ids, 8, err, sizeof(err));
+  CHECK(n == -1);
+
+  puts("test_models: ok");
+  return 0;
+}
+#endif