Issue 15 — No written threat model / invariants document

[Junman140]

Labels: documentation, security, priority:high
Body:

Problem
There's no document stating the system's core invariants (e.g., "total_supply(wPi) must never exceed verified Pi reserve," "only relayer-attested deposits can mint"). This is a prerequisite for any credible third-party audit.
Proposed fix
Write SECURITY.md covering: trust assumptions (admin key, relayer), invariants, known limitations, and out-of-scope items (e.g., current lack of proof-of-reserve).
Acceptance criteria

SECURITY.md merged
Linked from README

[akinboyewaSamson]

Hello,

I’m a smart contract and full-stack developer interested in contributing to this issue.

I have experience contributing through OnlyDust and have participated in Drips Wave 4, Wave 5, Wave 6, as well as the GrantFox beta campaign.

My technical background includes Rust, Soroban, Cairo, Solidity, and TypeScript, with a focus on building secure, scalable, and maintainable blockchain applications.

Based on the scope of this issue, I’m confident I can deliver a complete and well-tested solution within 10hours of assignment. I prioritize clean code, clear documentation, and efficient implementation.

I’d appreciate the opportunity to contribute and help move this issue forward.

Thank you.