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ADP-002 — Construction Hooks and Runtime Contracts

• Status: Approved & Implemented
• Deciders: Poppy Team
• Phase: Wave 1 (P00-G13 / P00-G14)

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Context

The language needed a unified, low-cognitive-overhead mechanism to validate struct states without requiring developers to write verbose boilerplate constructors or artificial getters and setters.

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Decisions Taken

1. init() Hook:

   • Executes immediately after struct field assignment during instantiation.
   • Used for structural validation, normalization, and rejecting invalid initial states with fail.

2. invariant() Invariants:

   • Declared directly in the struct body.
   • Evaluated upon creation and on all stable field mutations.
   • Predicate failures immediately reject the mutation.

3. Transactional Rollback inside attempt:

   • When mutations occur inside an attempt block, the VM maintains an in-memory rollback journal.
   • Any failure automatically restores pre-block state, guaranteeing atomic consistency.