improve shx upload error handling

bin/shx-upload

@@ -24,6 +24,44 @@ Notes:
 EOF
 }
 
+have_jq() {
+  command -v jq >/dev/null 2>&1
+}
+
+print_server_message() {
+  local response="$1"
+  local message=""
+
+  [[ -n "$response" ]] || return 0
+
+  if have_jq; then
+    message="$(
+      printf '%s\n' "$response" |
+        jq -r 'if type=="object" then .error // .message // .reason // empty else empty end' 2>/dev/null ||
+        true
+    )"
+  fi
+
+  if [[ -n "$message" ]]; then
+    echo "server: $message" >&2
+  else
+    echo "server response: $response" >&2
+  fi
+}
+
+response_has_files() {
+  local response="$1"
+
+  if have_jq; then
+    printf '%s\n' "$response" | jq -e '.files | arrays and length > 0' >/dev/null 2>&1
+    return $?
+  fi
+
+  [[ "$response" == *'"files"'* ]] || return 1
+  [[ "$response" =~ \"files\"[[:space:]]*:[[:space:]]*\[[[:space:]]*\] ]] && return 1
+  return 0
+}
+
 want_json=0
 if [[ "${1:-}" == "--help" || "${1:-}" == "-h" ]]; then
   usage
@@ -60,25 +98,47 @@ fi
 
 upload_one() {
   local file="$1"
+  local body_file http_code response
   if [[ ! -f "$file" ]]; then
     echo "error: file not found: $file" >&2
     return 1
   fi
 
-  local response
-  response="$(curl -fsS \
+  body_file="$(mktemp)"
+  if ! http_code="$(curl -sS \
+    -o "$body_file" \
+    -w '%{http_code}' \
     -H "authorization: $SHX_TOKEN" \
     "$SHX_URL/api/upload" \
-    -F "file=@$file")"
+    -F "file=@$file")"; then
+    rm -f "$body_file"
+    echo "error: upload request failed for $file" >&2
+    return 1
+  fi
+
+  response="$(cat "$body_file")"
+  rm -f "$body_file"
+
+  if [[ ! "$http_code" =~ ^2[0-9][0-9]$ ]]; then
+    echo "error: upload failed for $file (HTTP $http_code)" >&2
+    print_server_message "$response"
+    return 1
+  fi
+
+  if ! response_has_files "$response"; then
+    echo "error: upload response missing a non-empty .files array for $file" >&2
+    print_server_message "$response"
+    return 1
+  fi
 
   if [[ $want_json -eq 1 ]]; then
     printf '%s\n' "$response"
   else
-    if ! command -v jq >/dev/null 2>&1; then
+    if ! have_jq; then
       echo "error: jq is required unless --json is used" >&2
       return 1
     fi
-    printf '%s\n' "$response" | jq -r 'if .files then .files[] else . end'
+    printf '%s\n' "$response" | jq -r '.files[]'
   fi
 }