http_response() builds a JSON envelope wrapping the body. If the caller
previously called fs_read() (which sets _tl_fs_read_len = file_size),
http_worker used that stale value as the response copy length — truncating
the larger envelope to the original file size before it reached
http_send_response. The truncated envelope had the body field cut mid-string;
jp_parse_string_raw failed, env_body = "", and http_send_all sent file_size
bytes of garbage past the empty string.
Fix: reset _tl_fs_read_len = 0 at the start of http_response(). The hint
was set for the raw file bytes; the envelope is a new string and must use
strlen() for its length.
will.anderson