Feat/deterministic pseudorandomness abstraction (#558)

[Chucks1093]

Closes #558

Changes

• contracts/grainlify-core/src/pseudo_randomness.rs

  • Added a deterministic pseudo-randomness helper module for verifiable on-chain selection.
  • Implemented seed derivation from:
    • domain tag
    • context bytes
    • external seed (BytesN<32>)
  • Implemented candidate selection by per-candidate hash scoring (instead of simple modulo), reducing index/order bias.
  • Documented security trade-offs and adversarial examples (seed grinding, timing bias, candidate stuffing).

• contracts/grainlify-core/src/lib.rs

  • Exported shared helper via pub mod pseudo_randomness.

• contracts/bounty_escrow/contracts/escrow/src/lib.rs

  • Integrated deterministic selection into claim-ticket flow with:
    • derive_claim_ticket_winner_index(...)
    • derive_claim_ticket_winner(...)
    • issue_claim_ticket_deterministic(...)
  • Added deterministic selection context construction using contract/bounty/amount/expiry/timestamp/ticket-counter material.
  • Added new error variant for invalid selection input.

• contracts/bounty_escrow/contracts/escrow/src/events.rs

  • Added DeterministicSelectionDerived event for verifiable auditability of:
    • selected index
    • candidate count
    • selected beneficiary
    • seed hash
    • winner score

• contracts/bounty_escrow/contracts/escrow/src/test_deterministic_randomness.rs

  • Added deterministic randomness tests:
    • same inputs => same winner
    • order-independent winner selection for the same candidate set
    • deterministic ticket issuance matches derived winner

Testing

• contracts/grainlify-core

  • cargo test --lib ✅

• contracts/bounty_escrow/contracts/escrow

  • cargo fmt --check --all ✅
  • cargo test test_deterministic_randomness -- --nocapture ✅
  • cargo test --lib ✅
  • cargo test --lib invariant_checker_ci ✅

Notes

• This is deterministic pseudo-randomness, not true randomness.
• Verifiability is prioritized: any observer can recompute the selected winner from the published inputs.
• Manipulation resistance depends on seed/context discipline; consumers should prefer commit-reveal style external seeds and bounded submission windows where applicable.

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[Jagadeeshftw]

@Chucks1093 please resolve the conflicts

[Chucks1093]

@Jagadeeshftw please merge this

[Jagadeeshftw]

@Chucks1093 Can you please resolve the conflicts?