Observability: emit explicit participant loss outcome events during settlement #168

Summary

Complement payout/refund events with explicit loss outcome events for losing participants.

Why this matters

Analytics and user notifications need loss signals without inferring from absence of payout events.

Where to work

• contracts/src/contract.rs (settlement loops)
• contracts/src/tests/resolution.rs
• docs/EVENT_SCHEMA.md

What to implement

1. Emit outcome_loss (or equivalent) per losing user.
2. Include round id, mode, stake, and side/prediction metadata.
3. Add event assertions in both modes.

Acceptance Criteria

• Winners, losers, and refunds all have explicit event types.
• Event counts match participant outcomes.
• Schema docs updated.

Final result

Indexers no longer need heuristic loss detection.

Difficulty

intermediate