Enhanced Multi-Migration

Manage canister state evolution through a chain of migration modules. Each migration captures one logical change (add, rename, drop, transform a field) and the compiler verifies the entire chain is consistent.

When to Use

• Adding, removing, or renaming persistent actor fields
• Changing a field's type
• Restructuring state across canister upgrades
• Project has [canisters.<name>.migrations] configured in mops.toml

Critical Rules

• Never use stable keyword, preupgrade/postupgrade, or inline (with migration = ...)
• Actor variables are declared without initializers — values come from the migration chain
• The actor body must be static (no top-level side effects except <system> calls like timers)
• Each migration file exports public func migration({...}) : {...}
• Files are applied in lexicographic order — use timestamp prefixes