Program Escrow Event Ordering Guarantee

Overview

Soroban executes contract host functions sequentially within a transaction. Each call to env.events().publish() appends an event to the transaction's ordered event log. This means event topic order is deterministic and matches the exact call order of the invoking functions.

Off-chain indexers rely on this ordering to reconstruct an accurate, ordered activity feed for a program.

Payout Event Topics

Function	Event Topic	Struct
single_payout / single_payout_by	Payout	PayoutEvent
batch_payout / batch_payout_by	BatchPay	BatchPayoutEvent

Pause State-Change Event Topics

Function	Event Topics	Struct
set_paused	PauseSt (v1 legacy)	PauseStateChanged
	PauseStV2 (v2)	PauseStateChangedV2

Each call to set_paused emits two events per mode toggled: a legacy PauseSt event followed by a PauseStV2 event. If multiple modes are toggled in a single call (e.g., lock=true, release=true), four events are emitted in lock-then-release order.

Ordering Guarantee

Within a single Soroban transaction:

1. Events are appended to the log in the exact order the host function publish() is called.
2. There is no reordering, batching, or deferred emission.
3. When single_payout and batch_payout (or their _by variants) are invoked in sequence, the resulting Payout / BatchPay events appear in the precise call order.
4. Pause state-change events emitted by set_paused between payout calls are interleaved at their exact call position.

Example

single_payout(r1, 1000)       → emits Payout
set_paused(lock=true)         → emits PauseSt, PauseStV2
batch_payout([r2], [2000])    → emits BatchPay
set_paused(lock=false)        → emits PauseSt, PauseStV2

Event log (in order):

1. Payout
2. PauseSt (lock)
3. PauseStV2 (lock)
4. BatchPay
5. PauseSt (lock unpause)
6. PauseStV2 (lock unpause)

Implications for Indexers

• Events can be safely ordered by their position in the transaction event log.
• No secondary sort key (e.g., timestamp) is needed for within-transaction ordering.
• The version field (currently 2) on payout and pause V2 events enables schema evolution without breaking ordering assumptions.

Test Coverage

The deterministic event ordering for interleaved payout and pause calls is verified in:

• contracts/program-escrow/src/test_event_ordering.rs

Tests cover:

• Single-then-batch and batch-then-single ordering
• Four-call alternating sequence (single, batch, single, batch)
• Pause events interleaved between payouts
• Multi-mode pause (lock + release) between payouts
• Cross-run determinism (identical topic order across independent runs)
• V2 version tag presence on all payout events