ci: drop sanitizers job; harden test_subagent fake server

test_subagent segfaulted in the Docker runner: the fake SSE handler took
user + strlen(user) - 1 with an empty user string. Guard JSON access and
format the child report with an empty-safe last character. Remove the
sanitizers job entirely (if: false still queued it and blocked the runner).

.gitea/workflows/ci.yml

@@ -49,37 +49,6 @@ jobs:
           ./cst-agent --workspace "$PWD" --list-sessions
           ./cst-agent --demo-ctl --workspace .
 
-  # Disabled: Docker runner lacks SYS_PTRACE; ASan spins on DEADLYSIGNAL and
-  # wedged the only runner. Re-enable after the runner gets --cap-add SYS_PTRACE
-  # (or seccomp=unconfined).
-  sanitizers:
-    if: false
-    runs-on: ubuntu-latest
-    timeout-minutes: 15
-    steps:
-      - name: Checkout
-        env:
-          GITHUB_SERVER_URL: ${{ github.server_url }}
-          GITHUB_REPOSITORY: ${{ github.repository }}
-          GITHUB_SHA: ${{ github.sha }}
-        run: |
-          curl -fsSL "$GITHUB_SERVER_URL/$GITHUB_REPOSITORY/raw/commit/$GITHUB_SHA/scripts/ci_checkout.sh" \
-            -o /tmp/ci_checkout.sh
-          bash /tmp/ci_checkout.sh
-      - name: Install dependencies
-        run: |
-          SUDO=$(command -v sudo || true)
-          $SUDO bash scripts/ci_pkg_mirror.sh
-          $SUDO apt-get update
-          $SUDO apt-get install -y --no-install-recommends \
-            build-essential pkg-config libcurl4-openssl-dev libncurses-dev
-      - name: ASan + UBSan
-        timeout-minutes: 10
-        env:
-          ASAN_OPTIONS: abort_on_error=1:halt_on_error=1:detect_leaks=0:use_sigaltstack=0
-          UBSAN_OPTIONS: halt_on_error=1:print_stacktrace=1
-        run: timeout -s KILL 480 make asan
-
   musl:
     runs-on: ubuntu-latest
     timeout-minutes: 30

tests/test_subagent.c

@@ -93,7 +93,7 @@ static void reply_calls(test_sock_t fd, const char *const *calls, int n) {
     cJSON *tc = cJSON_AddArrayToObject(d, "tool_calls");
     cJSON *c = cJSON_CreateObject();
     cJSON_AddNumberToObject(c, "index", i);
-    char id[16];
+    char id[32];
     snprintf(id, sizeof(id), "call_%d", i);
     cJSON_AddStringToObject(c, "id", id);
     cJSON_AddStringToObject(c, "type", "function");
@@ -120,19 +120,30 @@ static int has_tool(const cJSON *body, const char *name) {
 
 static void handle(test_sock_t fd, const char *body_txt) {
   cJSON *body = cJSON_Parse(body_txt);
+  if (!body) {
+    const char *err = "HTTP/1.1 400 Bad Request\r\nConnection: close\r\n\r\n";
+    send_all(fd, err, strlen(err));
+    return;
+  }
   const cJSON *msgs = cJSON_GetObjectItemCaseSensitive(body, "messages");
-  int nm = cJSON_GetArraySize(msgs);
-  const cJSON *sys = cJSON_GetObjectItemCaseSensitive(
-      cJSON_GetArrayItem(msgs, 0), "content");
-  const cJSON *last = cJSON_GetArrayItem(msgs, nm - 1);
-  const char *last_role =
-      cJSON_GetObjectItemCaseSensitive(last, "role")->valuestring;
+  int nm = cJSON_IsArray(msgs) ? cJSON_GetArraySize(msgs) : 0;
+  const cJSON *sys = NULL;
+  const char *last_role = "";
   const char *user = "";
+  if (nm > 0) {
+    sys = cJSON_GetObjectItemCaseSensitive(cJSON_GetArrayItem(msgs, 0),
+                                           "content");
+    const cJSON *last = cJSON_GetArrayItem(msgs, nm - 1);
+    const cJSON *lr = cJSON_GetObjectItemCaseSensitive(last, "role");
+    if (cJSON_IsString(lr))
+      last_role = lr->valuestring;
+  }
   for (int i = 0; i < nm; i++) {
     const cJSON *m = cJSON_GetArrayItem(msgs, i);
     const cJSON *r = cJSON_GetObjectItemCaseSensitive(m, "role");
     const cJSON *c = cJSON_GetObjectItemCaseSensitive(m, "content");
-    if (strcmp(r->valuestring, "user") == 0 && cJSON_IsString(c))
+    if (cJSON_IsString(r) && strcmp(r->valuestring, "user") == 0 &&
+        cJSON_IsString(c))
       user = c->valuestring;
   }
   const char *hdr = "HTTP/1.1 200 OK\r\nContent-Type: text/event-stream\r\n"
@@ -160,8 +171,10 @@ static void handle(test_sock_t fd, const char *body_txt) {
       const char *calls[] = {"read_file", "{\"path\":\"a.txt\"}"};
       reply_calls(fd, calls, 1);
     } else {
-      char out[256];
-      snprintf(out, sizeof(out), "child report %s", user + strlen(user) - 1);
+      /* last char of the user prompt (e.g. "Find A" -> "A"); empty-safe */
+      char tag = user[0] ? user[strlen(user) - 1] : '?';
+      char out[64];
+      snprintf(out, sizeof(out), "child report %c", tag);
       reply_text(fd, out);
     }
     atomic_fetch_sub(&g_child_active, 1);