test(events): verify deterministic event emission order across contract operations

[Ajadu-Saviour]

Summary

This PR adds comprehensive event sequence tests to ensure all contract operations emit the expected events in the correct order. The new test suite validates the exact event count, topic symbols, and emission sequence, preventing regressions where events are emitted out of order, duplicated, or omitted during future refactoring.

Motivation

Many integrations rely on contract events for indexing, analytics, notifications, and off-chain processing. Changes to event emission order or missing events can silently break downstream consumers even when contract logic remains functionally correct.

This PR establishes deterministic event sequence validation to safeguard the contract's event interface.

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Changes

Event Sequence Validation

Added tests that capture the complete list of emitted events using:

env.events().all()

Each test validates:

• Exact number of emitted events
• Event topic symbols
• Event emission order
• Absence of unexpected events
• Presence of all expected events

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Covered Operations

Added event sequence assertions for all state-changing operations:

• create_shipment
• submit_proof
• confirm_milestone
• raise_dispute
• resolve_dispute
• cancel_shipment

Each operation is validated independently to ensure deterministic behavior.

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Strict Event Assertions

The test suite now fails if any of the following occur:

• Events are emitted in the wrong order
• An expected event is missing
• An additional event is emitted
• Event topics differ from the expected values
• Event count changes unexpectedly

This provides strong regression protection for event-driven integrations.

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Testing

Added comprehensive coverage for:

• Event count verification
• Topic symbol validation
• Event ordering
• Duplicate event detection
• Missing event detection
• Unexpected event detection
• Deterministic event emission across all supported operations

The tests rely on env.events().all() to validate the complete event stream after each contract call.

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Benefits

• Prevents accidental changes to event ordering during refactoring
• Protects downstream indexers and event consumers
• Ensures event contracts remain stable over time
• Improves confidence when modifying event emission logic
• Provides clear regression signals when event behavior changes

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Acceptance Criteria

• Added event sequence assertions for all six state-changing operations
• Verified exact event count for each operation
• Verified exact topic symbols
• Verified deterministic event ordering
• Tests fail on extra emitted events
• Tests fail on missing emitted events
• Tests remain resilient to internal event emission refactoring

Result

The contract now has deterministic event regression tests that enforce the exact sequence, count, and topics of emitted events, ensuring a stable event interface for off-chain consumers and reducing the risk of breaking changes during future development.

Closes #123