Architecture

An annual exchange rate that exists only months after the year ends, a cache keyed so that corrections cannot be stored, and three Postgres gotchas from making it immutable.

An instrument catalog looked mandatory for a tax engine. Its main attribute only decides whether an event happens, and the ledger already records that. Ask what each attribute changes before you maintain data for it.

End-to-end encryption fails when the server is the calculator. Disk encryption still lets the operator read everything. List what the computation needs, then give each reader its own zone and key.

Design notes from a Go MCP server in front of a shared password vault: annotations that never fire, schema tags that enforce nothing, a fence the JSON encoder rewrites, and error paths that talk to the model.