[Exchange] Reputation staking — agents stake believability on quality claims done

Goal

Enable agents to stake their reputation (believability score) on quality claims about
artifacts. If the claim proves correct (price moves in predicted direction), the agent's
believability increases. If wrong, it decreases. This creates skin-in-the-game for quality
assessments.

Acceptance Criteria

- agent_id — who is staking
- artifact_id — what they're staking on
- claim — 'high_quality' or 'low_quality'
- stake_amount — believability points at risk (0.01-0.1)
- target_price — predicted price threshold
- deadline — when to evaluate the stake
- outcome — 'correct', 'incorrect', 'pending'
- created_at

Dependencies

• exch-qm-02-PART — Participant accuracy tracking provides the framework

Dependents

• None (enrichment task)

Acceptance Criteria (updated status)

Work Log

2026-04-25 — Slot exch-qm-04-STAK

• Reviewed existing DB: quality_stakes table and quality_staking_leaderboard view already present from prior migration work
• Created scidex/exchange/quality_staking.py with:

- stake_on_artifact() — validates claim, stake_amount (0.01–0.10), 7-day min deadline, 10% max stake relative to current reputation_score, inserts into quality_stakes
- evaluate_pending_stakes() — scans expired pending stakes, compares price direction, updates outcome and agent_registry.reputation_score (±stake_amount × 1.5 / -stake_amount)
- get_agent_stakes() — history query for agent profile pages
- get_staking_leaderboard() — ranks agents by accuracy from the view

• Added 4 API routes to api.py (adjacent to existing exchange bid routes):

- POST /api/quality-stakes — place a stake
- GET /api/agents/{agent_id}/stakes — staking history
- GET /api/staking/leaderboard — accuracy rankings
- POST /api/staking/evaluate — trigger deadline evaluation

• Added staking history section to /senate/agent/{agent_id} profile page
• Validated with live DB: stake placement, validation rejections (short deadline, invalid claim, excess stake), leaderboard query
• Both files pass python3 -m py_compile

2026-04-26 — Merge retry (gate-fix)

• Previous merge attempt blocked by transient git index.lock on deploy server (not a code issue)
• Code verified unchanged: quality_staking.py compiles, all 4 API routes present in api.py
• Re-pushing to re-trigger merge pipeline