Detecting Conflicts

When the SAME package needs to satisfy DIFFERENT constraints from different parents, you have a conflict.

my-app
├── express ^4.0.0  (wants debug ^4.0.0)
└── mongoose ^7.0.0 (wants debug ^3.0.0)

debug ^4.0.0 and debug ^3.0.0 are INCOMPATIBLE (no version satisfies both).

Resolution strategies:

Allow multiple installations (npm, yarn): both versions go into the tree, in different paths. JS's module resolution lets each consumer use the version it asked for.

Force one version (Maven, gradle): pick the highest declared OR newest, fail if explicit conflict markers say otherwise. Java's classloader can only have one class per name — multiple versions break.

Backtrack (cargo, pip with resolver): try removing a constraint that's pinning incompatible versions. If we have mongoose ^7.0.0 requiring debug ^3.0.0 and express ^4.0.0 requiring debug ^4.0.0, the resolver might try mongoose ^6.0.0 to see if it allows debug ^4.0.0.

Report and fail (pubspec): give up, ask user to resolve. Friendly error messages are critical here.

For this lesson: conflict detection without resolution.