A field declared identically across multiple subclasses; the agent verifying changes to the field's shape must update every subclass consistently.
The field lives on the parent with one declaration; reading any subclass's storage resolves through inheritance to the parent's one field instead of paying the cost of loading every subclass to verify the declaration matches.
Before the refactoring
class Manager extends Employee { _name; }class Engineer extends Employee { _name; }
After the refactoring
class Employee { _name; }class Manager extends Employee {}class Engineer extends Employee {}
Refactoring the field's type or default requires the agent to touch every subclass; consistency drift hides bugs.
If subclasses use the field with different defaults, visibility, or semantic role, pulling up creates surprise behavior the agent must constantly disambiguate.
Changes to the field's type or default land in one parent declaration; generated code that constructs any subclass inherits the field without the agent having to verify that N subclasses still agree on the declaration.
Pulling up a field that subclasses use with different defaults or semantic roles creates one declaration the agent reads as shared; generated code that initializes the field at the parent level misses the subclass-specific values the original separate declarations carried.