v0.7.5: arrow keys, image request fix, deepseek-flash vision, musl CI

TUI keys: register both CSI and SS3 forms of the cursor/Home/End keys and
the xterm modifier sequences when terminfo lacks them, so an arrow sent in
the "other" form no longer turns into Esc + a typed letter. Up/Down move by
visual (soft-wrapped) row, and the draft survives a trip through history.
scripts/tui_keys drives the TUI in a pty to check all of this.

Images: text inside a multimodal content array is now a {"type":"text"}
part; DeepSeek rejected the bare string with HTTP 422. deepseek-flash
(and its deepseek-chat / deepseek-reasoner aliases) read images, so the
registry marks them vision; deepseek-v4-pro stays text only.

CI: models.c lost _DEFAULT_SOURCE in 0.7.0 and gmtime_r broke the musl
build; tests sleep with poll() instead of usleep for the same reason.

tests/test_llm_body.c

@@ -1,5 +1,7 @@
 #include "cJSON.h"
 #include "cst_agent.h"
+#include "cst_attach.h"
+#include "cst_test_util.h"
 
 #include <stdio.h>
 #include <stdlib.h>
@@ -325,8 +327,88 @@ static void test_images_off(void) {
   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);
+}
+
 int main(void) {
   test_images_off();
+  test_images_on();
   test_reasoning_and_prefix();
   test_cache_hints();
   test_tools_snapshot();