Verifiable exchange with replayable execution

Problem

An exchange screen cannot show whether its operator omitted an order, invented a fill, or replaced an earlier database. The project asks what an outside observer can verify from public data.

Constraints

• The demo had to remain auditable through public endpoints without database access or an operator account.
• Exact message bytes, integer price grids, and matching rules had to replay identically across implementations.
• The system uses synthetic markets. It does not hold funds, settle trades, replace a stopped sequencer, or prevent censorship.

What failed

• Unused-account trade and profit-and-loss queries scanned durable history. Bounded read paths and rate limits removed that cheap denial-of-service path.
• Passive visits persisted raw demo keys and the page could be framed. Key persistence became explicit and the deployment added browser security policies.
• Chart reads rebuilt candles and stale symbol responses could replace newer data. Bounded projections, cancellation, caching, and generation guards fixed both paths.
• Market partial fills and post-only or fill-or-kill refusals were correct but poorly explained. The ticket now states the price bound, slippage, fill, and cancelled remainder.

Tests and checks

• The public audit command downloads signed claims and messages, replays the history, and compares the resulting roots and trade counts.
• An architecture test keeps the validator implementation separate from the matcher it checks.
• Regression tests cover recovery, signatures, replay defense, order semantics, proofs, expensive empty-account queries, and browser security behavior.
• The public release uses one parentless commit whose files, Git objects, and container inputs were scanned before publication.