Custody engineering · Backend systems · Applied research
Field notes from systems where edge cases move money.
Bitcoin, EVM, Solana and the backend paths that turn chain state into balances, transactions and evidence. Written for engineers who need the failure modes, not a product overview.
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Custody engineering
SIGHASH Is a Security Parameter, Not a Construction Detail
Why Bitcoin signature hash modes belong in custody policy rather than transaction plumbing.
Balance at 14:00 UTC Does Not Exist
Chains never close, so a point-in-time balance has to be derived, not queried. The anchor problem, the per-chain traps, and why reproducibility is the real requirement.
A Multisig Nobody Can See
Taproot, MuSig2 and the operational trade-offs between privacy, cost and auditability in custody.
Upgradeable Tokens: Where Do the Balances Actually Live?
Delegatecall, proxy storage and the custody consequences of upgradeable token architecture.
Why Your Deposit Detection Misses Money
Proxy contracts, fee-on-transfer tokens, reorgs, UTXO edge cases and Solana token accounts - and why continuous reconciliation is the only real fix.
Transaction State Machines for Multi-Chain Custody
Broadcast is not done, confirmed is not final, and retries are where money gets lost. What breaks, chain by chain.
UTXO Coin Selection in Production
Your Bitcoin balance is not a number, it is a set. Fees, dust, privacy and the concurrency problem the tutorials skip.
Stuck Transactions at Scale
RBF, CPFP, nonce queues, expiring blockhashes and the pinning problem - a remediation playbook for transactions that will not confirm.
Engineering notes
Money in Rust: Making Illegal States Unrepresentable
Newtypes, phantom-typed currencies, checked arithmetic and typestate - how much of a financial bug class the compiler can take off your hands, for zero bytes.
Your Backtest Is Lying to You
Look-ahead bias, survivorship, point-in-time data and overfitting - why a backtest is a replay engine, and what that demands of it.
You Are Overfitting Your Training the Same Way You Overfit a Backtest
Why short training logs are noisy time series, and how to distinguish adherence from meaningful signal.
AI-assisted engineering
AI Coding Agents in Production: What Actually Changes
A field-tested operating model for using AI coding agents in production: context, task decomposition, review, guardrails and the real verification cost.
The Rules for Agent-Written Code in a Regulated Codebase Just Changed
A practical reading of AI-assisted engineering obligations and evidence expectations in regulated software delivery.