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

src/main.c

@@ -1,5 +1,6 @@
 #include "cst_agent.h"
 #include "cst_tools.h"
+#include "cst_version.h"
 #include "os_compat.h"
 
 #include <curl/curl.h>
@@ -26,7 +27,9 @@ static void usage(const char *argv0) {
           "  -N, --new             start a new session\n"
           "  -R, --resume ID       open a session by id or unique prefix\n"
           "  -L, --list-sessions   list sessions and exit\n"
-          "  -y, --yolo            never ask before shell / writes / web\n"
+          "  -A, --approval MODE   ask | auto (default: edits run, shell in\n"
+          "                        the sandbox or by safe rules) | yolo\n"
+          "  -y, --yolo            same as --approval yolo (this run only)\n"
           "  -C, --confirm LIST    shell,write,net (default) | none\n"
           "  -r, --protocol P      native-eos (default) | native-inc | ctl |\n"
           "                        ctl-heredoc | xml\n"
@@ -38,6 +41,7 @@ static void usage(const char *argv0) {
           "  -b, --api-base URL    OpenAI-compatible base URL (…/v1)\n"
           "  -s, --session FILE    explicit session file\n"
           "  -d, --demo-ctl        local CTL parser demo (no API)\n"
+          "  -V, --version         print the version and exit\n"
           "\n"
           "API keys: the TUI asks for a missing key and saves it per provider\n"
           "  in the config dir (credentials, mode 0600); /key changes it.\n"
@@ -48,7 +52,8 @@ static void usage(const char *argv0) {
           "      CST_CONFIRM CST_MAX_STEPS CST_TOOL_OUT_CAP CST_CTX_WINDOW\n"
           "      CST_CTX_TOKENS CST_AUTO_COMPACT=0 CST_SHELL_TIMEOUT\n"
           "      CST_METRICS=0 CST_RECORD_SSE CST_REPLAY_SSE CST_MODELS\n"
-          "      CST_AUTO_APPROVE=1 CST_SHELL CST_NO_PROJECT_NOTES=1 NO_COLOR\n"
+          "      CST_APPROVAL=ask|auto|yolo CST_AUTO_APPROVE=1 (=yolo)\n"
+          "      CST_SANDBOX=off CST_SHELL CST_NO_PROJECT_NOTES=1 NO_COLOR\n"
           "TUI: type /help inside for commands and keys\n",
           argv0);
 }
@@ -235,6 +240,15 @@ int main(int argc, char **argv) {
     return 1;
   }
 
+  int approval = -1;
+  const char *env_appr = getenv("CST_APPROVAL");
+  if (env_appr && env_appr[0] && cst_approval_parse(env_appr, &approval) != 0) {
+    fprintf(stderr, "bad CST_APPROVAL=%s (ask | auto | yolo)\n", env_appr);
+    return 1;
+  }
+  if (cfg.auto_approve)
+    approval = CST_APPROVAL_YOLO;
+
   int do_demo = 0;
   int force_ask_key = 0;
   int session_explicit = 0;
@@ -261,12 +275,14 @@ int main(int argc, char **argv) {
       {"resume", required_argument, 0, 'R'},
       {"list-sessions", no_argument, 0, 'L'},
       {"yolo", no_argument, 0, 'y'},
+      {"approval", required_argument, 0, 'A'},
       {"confirm", required_argument, 0, 'C'},
       {"effort", required_argument, 0, 'e'},
       {"help", no_argument, 0, 'h'},
+      {"version", no_argument, 0, 'V'},
       {0, 0, 0, 0}};
   int c;
-  while ((c = getopt_long(argc, argv, "w:s:b:k:m:P:r:n:T:Hp:dahNcR:LyC:e:", opts, NULL)) !=
+  while ((c = getopt_long(argc, argv, "w:s:b:k:m:P:r:n:T:Hp:dahVNcR:LyA:C:e:", opts, NULL)) !=
          -1) {
     switch (c) {
     case 'w':
@@ -334,7 +350,14 @@ int main(int argc, char **argv) {
       do_list = 1;
       break;
     case 'y':
-      cfg.auto_approve = 1;
+      approval = CST_APPROVAL_YOLO;
+      break;
+    case 'A':
+      if (cst_approval_parse(optarg, &approval) != 0) {
+        fprintf(stderr, "bad --approval %s (ask | auto | yolo)\n", optarg);
+        curl_global_cleanup();
+        return 1;
+      }
       break;
     case 'C':
       if (parse_confirm(optarg, &cfg) != 0) {
@@ -356,6 +379,10 @@ int main(int argc, char **argv) {
       usage(argv[0]);
       curl_global_cleanup();
       return 0;
+    case 'V':
+      printf("cst-agent %s\n", CST_VERSION);
+      curl_global_cleanup();
+      return 0;
     default:
       usage(argv[0]);
       curl_global_cleanup();
@@ -425,6 +452,12 @@ int main(int argc, char **argv) {
   while (alen > 0 && cfg.api_base[alen - 1] == '/')
     cfg.api_base[--alen] = 0;
 
+  /* Option > environment > last picked (settings.json) > auto. */
+  if (approval < 0 && cst_approval_parse(saved.approval, &approval) != 0)
+    approval = CST_DEFAULT_APPROVAL;
+  cfg.approval = approval;
+  cfg.auto_approve = approval == CST_APPROVAL_YOLO;
+
   /* Headless defaults to auto-approve shell/write (no interactive confirm). */
   if (cfg.headless)
     cfg.auto_approve = 1;