[Dimank92]

Summary

Resolves #202 by reconstructing the streams contract from a non-compiling shell into a fully functional Soroban smart contract implementing linear token streaming, stepped milestones, and cliff vesting.

Changes

1. Schedule Architecture:
   • Resolved Soroban contracttype macro enum limitations by converting Schedule variants from named fields to tuple variants: Linear, LinearWithCliff(u64), and Stepped(Vec<(u64, i128)>).
   • Implemented validate_schedule ensuring strictly increasing milestone checkpoints up to MAX_CHECKPOINTS (64) bounded within [start, end] and terminating at total.
2. Stream Lifecycle & Entrypoints:
   • create_stream & create_stream_stepped: upfront token deposit pull with TransferShortfall balance delta verification, preventing underfunded or fee-on-transfer shortfalls.
   • withdraw: allows recipients to withdraw accrued vested tokens computed via deterministic time-based curve.
   • cancel: funder or governance cancellation with exact pro-rata split (accrued balance paid to recipient, remainder refunded to funder).
   • transfer: recipient reassigns stream ownership and unwithdrawn accruals to a new recipient.
   • funding ops: top_up, extend_duration, increase_rate, and set_funding_delegate rebase the schedule via monotonic checkpoints so vested tokens never decrease.
   • schema_version, migrate, migrate_batch: fully integrated schema migration guards.
3. Spec-Conforming Events v2:
   • Implemented typed InitializedEvent, StreamCreatedEvent, WithdrawnEvent, StreamCanceledEvent, and StreamTransferredEvent conforming to events.json.
4. Testing:
   • 37/37 tests pass (cargo test -p zenith-streams), including unit tests, adversarial token tests, and proptests (prop_withdrawn_never_exceeds_deposit, prop_withdrawable_never_decreases, prop_vested_is_monotonic_across_funding_calls).
   • Clean Clippy check with zero warnings (cargo clippy -p zenith-streams --tests --no-deps -- -D warnings).

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Payout Wallet: 0xC345C07229307d4f1c7935aD2cAe48e390215808 (Polygon / Base / Arbitrum / Stellar)