NPCs fail to appear after writing new values to the packfile.

[DarkDragon]

Oh, sweet dear little baby infant Jesus.....

Please, please, pleeeease, be extremely careful when changing packfile formats. Even I go into "serious mode" when doing anything with that file.

This exactly.

There is unfortunately nothing "automatic" about the quest file format. The procedure for adding a field to the quest file is

1. Increment the appropriate section version number
2. Write the save code. Ensure you use the right packfile write command (bit length, endianness, etc) for the type of data you're trying to save.
3. In the quest loading code (in qst.cpp) in the place where you want to read in the new data, add a check for the section version number
- if it's less than the new version number, do NOT attempt to read the new data, but set the values for the new field to some reasonable default instead;
-- IMPORTANT: you might need to do this in several places in the code. Here is some fairly typical code structure:

if(s_version <= 2.0)
{
   // some code for loading legacy 1.90 quests
}
else
{
  // a **huge** block of code for loading modern quests
  
  if(s_version <= 6.0)
  {
    // some code for handling 2.10 quests
  }
  else
  {
    // another huge block

    // here is where you want to read in your new field
  }
}

You need to make sure you cover *all possible* code paths when reading in the quest, and set default values correctly for all cases. In the example above, you will have to add code to set defaults in at least three places. There have been dozens of bugs in the past due to the old quest loading code not being updated properly as new fields are added.
- otherwise, read in the data from the file (using a matching command to the write command, obviously).

Then you test the shit out of the code, on both old quests and newly-created ones. The best-case scenario for a bug here is massive corruption when you try to load old quests. The worst case is a subtle bug that corrupts a quest only when it is loaded and then re-saved in ZQuest, totally screwing any quest author who encounters the bug and doesn't have regular backups of their WIP (yes, we tell them not to work on major projects using betas or RCs, but...)