newc dev field cant be 0

in the packer, if dev (or a number of others) are nullish, including 0 because js Is js, then it sets them to defaults. the default for dev is not 0, it is 777777 octal, which means you cannot set dev to 0.
suggested fix: either make the default 0, or exclude 0 from the override by using "this = this ?? that" instead of "if (!this) this = that" in pack.js.

Start in pack.js and inspect how nullish packer fields are replaced with defaults. Ensure an explicit dev value of 0 is preserved rather than treated as missing, then verify that packing with dev set to 0 produces the requested value instead of the default.

Written by the indexing model from the issue text.