CST-agent/tests/test_llm_body.c

#include "cJSON.h"
#include "cst_agent.h"
#include "cst_attach.h"
#include "cst_test_util.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static int nfail;

#define EXPECT(cond, msg)                                                      \
  do {                                                                         \
    if (!(cond)) {                                                             \
      fprintf(stderr, "FAIL %s:%d: %s\n", __FILE__, __LINE__, msg);            \
      nfail++;                                                                 \
    }                                                                          \
  } while (0)

static cst_message_t msg(cst_role_t role, const char *content) {
  cst_message_t m;
  memset(&m, 0, sizeof(m));
  m.role = role;
  m.content = (char *)content;
  return m;
}

static cJSON *build(const cst_message_t *msgs, int n, int tools,
                    size_t tool_cap) {
  cst_llm_request_t r;
  memset(&r, 0, sizeof(r));
  r.model = "test-model";
  r.msgs = msgs;
  r.nmsgs = n;
  r.enable_tools = tools;
  r.tool_out_cap = tool_cap;
  char *body = cst_llm_build_body(&r);
  EXPECT(body != NULL, "body built");
  cJSON *j = body ? cJSON_Parse(body) : NULL;
  EXPECT(j != NULL, "body is valid JSON");
  free(body);
  return j;
}

static const char *content_at(const cJSON *root, int i) {
  const cJSON *msgs = cJSON_GetObjectItemCaseSensitive(root, "messages");
  const cJSON *m = cJSON_GetArrayItem(msgs, i);
  const cJSON *c = cJSON_GetObjectItemCaseSensitive(m, "content");
  return cJSON_IsString(c) ? c->valuestring : NULL;
}

static const char *role_at(const cJSON *root, int i) {
  const cJSON *msgs = cJSON_GetObjectItemCaseSensitive(root, "messages");
  const cJSON *m = cJSON_GetArrayItem(msgs, i);
  const cJSON *r = cJSON_GetObjectItemCaseSensitive(m, "role");
  return cJSON_IsString(r) ? r->valuestring : "";
}

static int nmsgs(const cJSON *root) {
  return cJSON_GetArraySize(cJSON_GetObjectItemCaseSensitive(root, "messages"));
}

/* TAB / quotes / backslash / control bytes / CJK must survive verbatim
 * (the old hand-rolled escaper turned a Makefile TAB into HTTP 400). */
static void test_escaping(void) {
  const char *text = "all:\n\tgcc -o \"a b\" x.c \\\n\x01\x1f end 中文";
  cst_message_t m[2] = {msg(CST_ROLE_SYSTEM, "sys"), msg(CST_ROLE_USER, text)};
  cJSON *j = build(m, 2, 0, 0);
  const char *c = content_at(j, 1);
  EXPECT(c && strcmp(c, text) == 0, "user content roundtrips exactly");
  EXPECT(!cJSON_GetObjectItemCaseSensitive(j, "tools"), "no tools when off");
  const cJSON *so = cJSON_GetObjectItemCaseSensitive(j, "stream_options");
  EXPECT(cJSON_IsTrue(cJSON_GetObjectItemCaseSensitive(so, "include_usage")),
         "stream_options.include_usage");
  cJSON_Delete(j);
}

/* Settings -> Advanced: the generation parameters go on the wire only when
 * they were set. An absent field is the provider's own default, which
 * "temperature": 0 would not be. */
static void test_gen_params(void) {
  cst_message_t m[1] = {msg(CST_ROLE_USER, "hi")};
  cst_llm_request_t r;
  memset(&r, 0, sizeof(r));
  r.model = "test-model";
  r.msgs = m;
  r.nmsgs = 1;
  r.temperature = 0.2;
  r.top_p = 0.9;
  r.max_tokens = 4096;
  char *body = cst_llm_build_body(&r);
  EXPECT(body != NULL, "body with parameters");
  cJSON *j = body ? cJSON_Parse(body) : NULL;
  free(body);
  const cJSON *t = cJSON_GetObjectItemCaseSensitive(j, "temperature");
  const cJSON *p = cJSON_GetObjectItemCaseSensitive(j, "top_p");
  const cJSON *mt = cJSON_GetObjectItemCaseSensitive(j, "max_tokens");
  EXPECT(cJSON_IsNumber(t) && t->valuedouble > 0.19 && t->valuedouble < 0.21,
         "temperature is sent as a number");
  EXPECT(cJSON_IsNumber(p) && cJSON_IsNumber(mt) && mt->valueint == 4096,
         "top_p and max_tokens are sent");
  cJSON_Delete(j);
  /* unset: none of the three is in the body at all */
  cJSON *plain = build(m, 1, 0, 0);
  EXPECT(!cJSON_GetObjectItemCaseSensitive(plain, "temperature") &&
             !cJSON_GetObjectItemCaseSensitive(plain, "top_p") &&
             !cJSON_GetObjectItemCaseSensitive(plain, "max_tokens"),
         "an unset parameter is not sent at all");
  cJSON_Delete(plain);
}

static void test_invalid_utf8(void) {
  const char text[] = "ok \xff\xfe bad \xe4\xb8 trunc";
  cst_message_t m[1] = {msg(CST_ROLE_USER, text)};
  cJSON *j = build(m, 1, 0, 0);
  const char *c = content_at(j, 0);
  EXPECT(c != NULL, "content present");
  EXPECT(c && strlen(c) == strlen(text), "sanitize keeps byte length");
  EXPECT(c && strstr(c, "ok ") == c, "valid prefix kept");
  cJSON_Delete(j);
}

static void test_tool_calls_and_null_content(void) {
  cst_message_t m[3];
  m[0] = msg(CST_ROLE_USER, "go");
  m[1] = msg(CST_ROLE_ASSISTANT, "");
  m[1].tool_calls_json =
      "[{\"id\":\"c1\",\"type\":\"function\",\"function\":{\"name\":"
      "\"read_file\",\"arguments\":\"{\\\"path\\\":\\\"a\\tb.c\\\"}\"}}]";
  m[2] = msg(CST_ROLE_TOOL, "[tool read_file id=c1 exit=0]\nhello");
  snprintf(m[2].tool_call_id, sizeof(m[2].tool_call_id), "c1");
  cJSON *j = build(m, 3, 1, 0);
  const cJSON *msgs = cJSON_GetObjectItemCaseSensitive(j, "messages");
  const cJSON *a = cJSON_GetArrayItem(msgs, 1);
  EXPECT(cJSON_IsNull(cJSON_GetObjectItemCaseSensitive(a, "content")),
         "assistant content null with tool_calls");
  const cJSON *tc = cJSON_GetObjectItemCaseSensitive(a, "tool_calls");
  EXPECT(cJSON_IsArray(tc) && cJSON_GetArraySize(tc) == 1, "tool_calls kept");
  const cJSON *t = cJSON_GetArrayItem(msgs, 2);
  EXPECT(strcmp(role_at(j, 2), "tool") == 0, "tool role");
  const cJSON *tid = cJSON_GetObjectItemCaseSensitive(t, "tool_call_id");
  EXPECT(cJSON_IsString(tid) && strcmp(tid->valuestring, "c1") == 0,
         "tool_call_id");
  const cJSON *tools = cJSON_GetObjectItemCaseSensitive(j, "tools");
  /* The exact set depends on the host: a tool whose platform probe fails is
   * offered nowhere, so look for a core tool instead of counting. */
  char *tj = tools ? cJSON_PrintUnformatted(tools) : NULL;
  EXPECT(cJSON_IsArray(tools) && cJSON_GetArraySize(tools) >= 4 && tj &&
             strstr(tj, "read_file") != NULL,
         "tools[] schema present");
  free(tj);
  const cJSON *choice = cJSON_GetObjectItemCaseSensitive(j, "tool_choice");
  EXPECT(cJSON_IsString(choice) && strcmp(choice->valuestring, "auto") == 0,
         "tool_choice auto");
  cJSON_Delete(j);
}

static void test_merge_and_orphan_tool(void) {
  cst_message_t m[3];
  m[0] = msg(CST_ROLE_USER, "first");
  m[1] = msg(CST_ROLE_TOOL, "orphan output"); /* no id -> user text */
  m[2] = msg(CST_ROLE_USER, "third");
  cJSON *j = build(m, 3, 0, 0);
  EXPECT(nmsgs(j) == 1, "consecutive user messages merged");
  const char *c = content_at(j, 0);
  EXPECT(c && strstr(c, "first") && strstr(c, "orphan output") &&
             strstr(c, "third"),
         "merged content keeps all parts in order");
  cJSON_Delete(j);
}

static void test_tool_cap_head_tail(void) {
  size_t n = 100000;
  char *big = malloc(n + 1);
  memset(big, 'x', n);
  memcpy(big, "HEAD", 4);
  memcpy(big + n - 4, "TAIL", 4);
  big[n] = 0;
  cst_message_t m[3];
  m[0] = msg(CST_ROLE_USER, "go");
  m[1] = msg(CST_ROLE_ASSISTANT, "");
  m[1].tool_calls_json = "[{\"id\":\"c1\",\"type\":\"function\",\"function\":"
                         "{\"name\":\"run_shell\",\"arguments\":\"{}\"}}]";
  m[2] = msg(CST_ROLE_TOOL, big);
  snprintf(m[2].tool_call_id, sizeof(m[2].tool_call_id), "c1");
  cJSON *j = build(m, 3, 1, 1000);
  const char *c = content_at(j, 2);
  EXPECT(c && strlen(c) < 1200, "tool output capped");
  EXPECT(c && strncmp(c, "HEAD", 4) == 0, "head kept");
  EXPECT(c && strcmp(c + strlen(c) - 4, "TAIL") == 0, "tail kept");
  EXPECT(c && strstr(c, "omitted"), "omission note");
  cJSON_Delete(j);

  /* user text (e.g. text-protocol result frames) is never capped */
  cst_message_t u[1] = {msg(CST_ROLE_USER, big)};
  j = build(u, 1, 0, 1000);
  c = content_at(j, 0);
  EXPECT(c && strlen(c) == n, "user text not capped");
  cJSON_Delete(j);
  free(big);
}

static cJSON *build_req(const cst_llm_request_t *r) {
  char *body = cst_llm_build_body(r);
  EXPECT(body != NULL, "body built");
  cJSON *j = body ? cJSON_Parse(body) : NULL;
  EXPECT(j != NULL, "body is valid JSON");
  free(body);
  return j;
}

static const cJSON *msg_at(const cJSON *root, int i) {
  return cJSON_GetArrayItem(cJSON_GetObjectItemCaseSensitive(root, "messages"),
                            i);
}

static const cJSON *cache_mark(const cJSON *m) {
  const cJSON *c = cJSON_GetObjectItemCaseSensitive(m, "content");
  if (!cJSON_IsArray(c))
    return NULL;
  const cJSON *last = cJSON_GetArrayItem(c, cJSON_GetArraySize(c) - 1);
  return cJSON_GetObjectItemCaseSensitive(last, "cache_control");
}

static void test_reasoning_and_prefix(void) {
  cst_message_t m[4];
  m[0] = msg(CST_ROLE_SYSTEM, "sys");
  m[1] = msg(CST_ROLE_USER, "go");
  m[2] = msg(CST_ROLE_ASSISTANT, "partial answer");
  m[2].reasoning = "thinking it over";
  m[3] = msg(CST_ROLE_ASSISTANT, "cut off here");
  m[3].prefix = 1;
  cst_llm_request_t r;
  memset(&r, 0, sizeof(r));
  r.model = "deepseek-flash";
  r.msgs = m;
  r.nmsgs = 4;
  cJSON *j = build_req(&r);
  EXPECT(!cJSON_GetObjectItemCaseSensitive(msg_at(j, 2), "reasoning_content"),
         "reasoning only when asked for");
  const cJSON *p = cJSON_GetObjectItemCaseSensitive(msg_at(j, 3), "prefix");
  EXPECT(cJSON_IsTrue(p), "prefix:true on the continued message");
  EXPECT(!cJSON_GetObjectItemCaseSensitive(msg_at(j, 2), "prefix"),
         "no prefix on history");
  cJSON_Delete(j);

  r.send_reasoning = 1;
  j = build_req(&r);
  const cJSON *rc =
      cJSON_GetObjectItemCaseSensitive(msg_at(j, 2), "reasoning_content");
  EXPECT(cJSON_IsString(rc) && strcmp(rc->valuestring, "thinking it over") == 0,
         "reasoning_content passed back");
  EXPECT(!cJSON_GetObjectItemCaseSensitive(j, "prompt_cache_key"),
         "no cache key without a cache style");
  cJSON_Delete(j);
}

static void test_cache_hints(void) {
  cst_message_t m[4];
  m[0] = msg(CST_ROLE_SYSTEM, "sys");
  m[1] = msg(CST_ROLE_USER, "first");
  m[2] = msg(CST_ROLE_ASSISTANT, "reply");
  m[3] = msg(CST_ROLE_USER, "second");
  cst_llm_request_t r;
  memset(&r, 0, sizeof(r));
  r.model = "gpt-4.1";
  r.msgs = m;
  r.nmsgs = 4;
  r.cache_style = CST_CACHE_OPENAI;
  r.cache_key = "sess-1";
  cJSON *j = build_req(&r);
  const cJSON *k = cJSON_GetObjectItemCaseSensitive(j, "prompt_cache_key");
  EXPECT(cJSON_IsString(k) && strcmp(k->valuestring, "sess-1") == 0,
         "prompt_cache_key");
  EXPECT(content_at(j, 3) && !cache_mark(msg_at(j, 3)),
         "OpenAI style leaves content as strings");
  cJSON_Delete(j);

  r.model = "anthropic/claude-sonnet-4";
  r.cache_style = CST_CACHE_ANTHROPIC;
  r.cache_ttl = "1h";
  j = build_req(&r);
  EXPECT(!cJSON_GetObjectItemCaseSensitive(j, "prompt_cache_key"),
         "no prompt_cache_key for Anthropic");
  const cJSON *cs = cache_mark(msg_at(j, 0));
  const cJSON *cl = cache_mark(msg_at(j, 3));
  const cJSON *cu = cache_mark(msg_at(j, 1));
  EXPECT(cs && cl && cu, "breakpoints on system, newest, previous user");
  EXPECT(!cache_mark(msg_at(j, 2)), "no breakpoint on the assistant reply");
  const cJSON *ttl = cJSON_GetObjectItemCaseSensitive(cl, "ttl");
  EXPECT(cJSON_IsString(ttl) && strcmp(ttl->valuestring, "1h") == 0, "ttl");
  const cJSON *parts =
      cJSON_GetObjectItemCaseSensitive(msg_at(j, 3), "content");
  const cJSON *txt =
      cJSON_GetObjectItemCaseSensitive(cJSON_GetArrayItem(parts, 0), "text");
  EXPECT(cJSON_IsString(txt) && strcmp(txt->valuestring, "second") == 0,
         "marked content keeps its text");
  cJSON_Delete(j);
}

static void test_tools_snapshot(void) {
  cst_message_t m[1] = {msg(CST_ROLE_USER, "go")};
  cst_llm_request_t r;
  memset(&r, 0, sizeof(r));
  r.model = "test-model";
  r.msgs = m;
  r.nmsgs = 1;
  r.enable_tools = 1;
  r.tools_json = "[{\"type\":\"function\",\"function\":{\"name\":\"only_me\","
                 "\"parameters\":{\"type\":\"object\"}}}]";
  cJSON *j = build_req(&r);
  const cJSON *tools = cJSON_GetObjectItemCaseSensitive(j, "tools");
  EXPECT(cJSON_IsArray(tools) && cJSON_GetArraySize(tools) == 1,
         "tools[] taken from the snapshot");
  const cJSON *nm = cJSON_GetObjectItemCaseSensitive(
      cJSON_GetObjectItemCaseSensitive(cJSON_GetArrayItem(tools, 0),
                                       "function"),
      "name");
  EXPECT(cJSON_IsString(nm) && strcmp(nm->valuestring, "only_me") == 0,
         "snapshot tool name");
  cJSON_Delete(j);
}

static void test_images_off(void) {
  cst_attachment_t img;
  memset(&img, 0, sizeof(img));
  snprintf(img.id, sizeof(img.id), "img-1");
  snprintf(img.rel, sizeof(img.rel), "img-1.png");
  snprintf(img.name, sizeof(img.name), "shot.png");
  snprintf(img.mime, sizeof(img.mime), "image/png");
  img.width = 640;
  img.height = 480;
  img.bytes = 2048;
  cst_message_t m[4];
  m[0] = msg(CST_ROLE_USER, "what is this");
  m[0].attach = &img;
  m[0].nattach = 1;
  m[1] = msg(CST_ROLE_ASSISTANT, "");
  m[1].tool_calls_json = "[{\"id\":\"c1\",\"type\":\"function\",\"function\":"
                         "{\"name\":\"view_image\",\"arguments\":\"{}\"}}]";
  m[2] = msg(CST_ROLE_TOOL, "view_image shot.png");
  snprintf(m[2].tool_call_id, sizeof(m[2].tool_call_id), "c1");
  m[2].attach = &img;
  m[2].nattach = 1;
  m[3] = msg(CST_ROLE_USER, "and now?");
  cst_llm_request_t r;
  memset(&r, 0, sizeof(r));
  r.model = "deepseek-flash";
  r.msgs = m;
  r.nmsgs = 4;
  r.images_off = 1;
  r.session_path = "/nonexistent/s.jsonl";
  cJSON *j = build_req(&r);
  char *s = cJSON_PrintUnformatted(j);
  EXPECT(s && !strstr(s, "image_url"), "no image parts when images are off");
  free(s);
  const char *c0 = content_at(j, 0);
  EXPECT(c0 && strstr(c0, "what is this") &&
             strstr(c0, "[image \"shot.png\" (640x480") &&
             strstr(c0, "not sent: this model does not take images"),
         "user image becomes a plain-text note");
  const char *c2 = content_at(j, 2);
  EXPECT(c2 && strstr(c2, "view_image shot.png") && strstr(c2, "not sent"),
         "tool image noted inside the tool result");
  EXPECT(nmsgs(j) == 4, "no extra user message for deferred tool images");
  cJSON_Delete(j);
}

/* Every element of every content array must be a typed part object. */
static int parts_typed(const cJSON *root) {
  const cJSON *m;
  cJSON_ArrayForEach(m, cJSON_GetObjectItemCaseSensitive(root, "messages")) {
    const cJSON *c = cJSON_GetObjectItemCaseSensitive(m, "content");
    if (!cJSON_IsArray(c))
      continue;
    const cJSON *p;
    cJSON_ArrayForEach(p, c) {
      const cJSON *t = cJSON_GetObjectItemCaseSensitive(p, "type");
      if (!cJSON_IsObject(p) || !cJSON_IsString(t))
        return 0;
    }
  }
  return 1;
}

static void test_images_on(void) {
  char dir[1024], sess[1100], err[256];
  if (test_tmpdir(dir, sizeof(dir), "cst-body") != 0) {
    EXPECT(0, "scratch dir");
    return;
  }
  snprintf(sess, sizeof(sess), "%s/s.jsonl", dir);
  static const unsigned char png[32] = {0x89, 'P', 'N', 'G', '\r', '\n', 0x1A,
                                        '\n', 0, 0, 0, 13, 'I', 'H', 'D', 'R',
                                        0, 0, 0, 2, 0, 0, 0, 2};
  cst_attachment_t *img = cst_attach_import_bytes(sess, "shot.png",
                                                  (const char *)png,
                                                  sizeof(png), err, sizeof(err));
  EXPECT(img != NULL, "image stored");
  if (!img)
    return;
  cst_attachment_t gone = *img;
  snprintf(gone.rel, sizeof(gone.rel), "missing.png");
  cst_message_t m[5];
  m[0] = msg(CST_ROLE_USER, "what is this");
  m[0].attach = img;
  m[0].nattach = 1;
  m[1] = msg(CST_ROLE_ASSISTANT, "");
  m[1].tool_calls_json = "[{\"id\":\"c1\",\"type\":\"function\",\"function\":"
                         "{\"name\":\"view_image\",\"arguments\":\"{}\"}}]";
  m[2] = msg(CST_ROLE_TOOL, "view_image shot.png");
  snprintf(m[2].tool_call_id, sizeof(m[2].tool_call_id), "c1");
  m[2].attach = img;
  m[2].nattach = 1;
  m[3] = msg(CST_ROLE_USER, "and now?");
  m[4] = msg(CST_ROLE_USER, "");
  m[4].attach = &gone;
  m[4].nattach = 1;
  cst_llm_request_t r;
  memset(&r, 0, sizeof(r));
  r.model = "deepseek-flash";
  r.msgs = m;
  r.nmsgs = 5;
  r.session_path = sess;
  cJSON *j = build_req(&r);
  EXPECT(parts_typed(j), "content arrays hold only typed parts");
  const cJSON *p0 = cJSON_GetObjectItemCaseSensitive(
      cJSON_GetArrayItem(cJSON_GetObjectItemCaseSensitive(j, "messages"), 0),
      "content");
  const cJSON *t0 = cJSON_GetObjectItemCaseSensitive(
      cJSON_GetArrayItem(p0, 0), "text");
  const cJSON *u1 = cJSON_GetObjectItemCaseSensitive(
      cJSON_GetObjectItemCaseSensitive(cJSON_GetArrayItem(p0, 1), "image_url"),
      "url");
  EXPECT(cJSON_IsString(t0) && strcmp(t0->valuestring, "what is this") == 0,
         "user text is a text part");
  EXPECT(cJSON_IsString(u1) &&
             strncmp(u1->valuestring, "data:image/png;base64,", 22) == 0,
         "image is a data URL part");
  char *s = cJSON_PrintUnformatted(j);
  EXPECT(s && strstr(s, "and now?") && strstr(s, "not sent"),
         "follow-up text and the missing-image note are parts too");
  free(s);
  cJSON_Delete(j);
  cst_attach_free(img);
}

/* Every text part of message i, joined (malloc'd, "" when there is none). */
static char *text_of(const cJSON *root, int i) {
  const cJSON *m =
      cJSON_GetArrayItem(cJSON_GetObjectItemCaseSensitive(root, "messages"), i);
  const cJSON *c = cJSON_GetObjectItemCaseSensitive(m, "content");
  if (cJSON_IsString(c)) {
    size_t n = strlen(c->valuestring);
    char *out = malloc(n + 1);
    if (out)
      memcpy(out, c->valuestring, n + 1);
    return out;
  }
  size_t len = 1;
  const cJSON *p, *t, *s;
  cJSON_ArrayForEach(p, c) {
    t = cJSON_GetObjectItemCaseSensitive(p, "type");
    s = cJSON_GetObjectItemCaseSensitive(p, "text");
    if (cJSON_IsString(t) && strcmp(t->valuestring, "text") == 0 &&
        cJSON_IsString(s))
      len += strlen(s->valuestring) + 1;
  }
  char *out = calloc(1, len);
  if (!out)
    return NULL;
  cJSON_ArrayForEach(p, c) {
    t = cJSON_GetObjectItemCaseSensitive(p, "type");
    s = cJSON_GetObjectItemCaseSensitive(p, "text");
    if (cJSON_IsString(t) && strcmp(t->valuestring, "text") == 0 &&
        cJSON_IsString(s)) {
      strcat(out, s->valuestring);
      strcat(out, "\n");
    }
  }
  return out;
}

/* A document is inlined as text, so a text-only model and a message that
 * also carries an image both keep it; the image is what becomes a note. */
static void test_document_parts(void) {
  char dir[1024], sess[1100], err[256], src[1200];
  if (test_tmpdir(dir, sizeof(dir), "cst-body-doc") != 0) {
    EXPECT(0, "scratch dir");
    return;
  }
  snprintf(sess, sizeof(sess), "%s/s.jsonl", dir);
  snprintf(src, sizeof(src), "%s/paper.pdf", dir);
  static const char PDF[] =
      "%PDF-1.4\n"
      "1 0 obj\n<< /Type /Catalog /Pages 2 0 R >>\nendobj\n"
      "2 0 obj\n<< /Type /Pages /Kids [3 0 R] /Count 1 >>\nendobj\n"
      "3 0 obj\n<< /Type /Page /Parent 2 0 R /Resources << /Font << /F1 4 0 R "
      ">> >> /Contents 5 0 R >>\nendobj\n"
      "4 0 obj\n<< /Type /Font /Subtype /Type1 /BaseFont /Helvetica >>\n"
      "endobj\n"
      "5 0 obj\n<< >>\nstream\n"
      "BT /F1 12 Tf 72 720 Td (Inlined paper text) Tj ET\n"
      "endstream\nendobj\n"
      "trailer\n<< /Root 1 0 R >>\n%%EOF\n";
  FILE *f = fopen(src, "wb");
  EXPECT(f != NULL, "write the PDF");
  if (!f)
    return;
  fwrite(PDF, 1, strlen(PDF), f);
  fclose(f);
  cst_attachment_t *doc = cst_attach_import_file(sess, src, err, sizeof(err));
  EXPECT(doc != NULL, "PDF stored");
  if (!doc)
    return;
  static const unsigned char png[32] = {0x89, 'P', 'N', 'G', '\r', '\n', 0x1A,
                                        '\n', 0, 0, 0, 13, 'I', 'H', 'D', 'R',
                                        0, 0, 0, 2, 0, 0, 0, 2};
  cst_attachment_t *img = cst_attach_import_bytes(
      sess, "shot.png", (const char *)png, sizeof(png), err, sizeof(err));
  EXPECT(img != NULL, "image stored");
  if (!img) {
    cst_attach_free(doc);
    return;
  }
  cst_attachment_t both[2] = {*doc, *img};
  cst_message_t m[2];
  m[0] = msg(CST_ROLE_USER, "what does this say?");
  m[0].attach = both;
  m[0].nattach = 2;
  m[1] = msg(CST_ROLE_USER, "thanks");
  cst_llm_request_t r;
  memset(&r, 0, sizeof(r));
  r.model = "deepseek-flash";
  r.msgs = m;
  r.nmsgs = 2;
  r.images_off = 1; /* a text-only model */
  r.session_path = sess;
  cJSON *j = build_req(&r);
  char *txt = text_of(j, 0);
  EXPECT(txt && strstr(txt, "[document \"paper.pdf\"") &&
             strstr(txt, "Inlined paper text") &&
             strstr(txt, "[-- end of document --]"),
         "the PDF text is inlined even when images are off");
  EXPECT(txt && strstr(txt, "[image \"shot.png\"") && strstr(txt, "not sent"),
         "the image beside it is still only a note");
  free(txt);
  char *s = cJSON_PrintUnformatted(j);
  EXPECT(s && !strstr(s, "image_url"), "no image part with images off");
  free(s);
  cJSON_Delete(j);
  cst_attach_free(doc);
  cst_attach_free(img);
}

int main(void) {
  test_images_off();
  test_images_on();
  test_document_parts();
  test_reasoning_and_prefix();
  test_cache_hints();
  test_tools_snapshot();
  test_gen_params();
  test_escaping();
  test_invalid_utf8();
  test_tool_calls_and_null_content();
  test_merge_and_orphan_tool();
  test_tool_cap_head_tail();
  if (nfail) {
    fprintf(stderr, "test_llm_body: %d failed\n", nfail);
    return 1;
  }
  printf("test_llm_body: OK\n");
  return 0;
}