notes
Things I wrote down so I'd stop re-learning them.
Each note starts from something that went wrong, or nearly did, in a system I built, and ends with the rule I keep because of it.
- 9 Oct 2026Unmeasured is not zeroWhat I learned building a per-user ledger for every token, page and image an AI service pays for, and why “we don't know” has to be a value.cost · observability · 5 mindraft
- 9 Oct 2026Spreadsheets are not documentsWhy chunk-and-embed fails on spreadsheets, what replaced it, and the two independent locks on SQL a model writes.retrieval · sql · safety · 5 mindraft
- 9 Oct 2026Never hand the model the keysHow an agent can work in someone's mailbox without the model ever holding their credentials, and the four-times “send it?” bug that moved approval out of the tool.agents · safety · mcp · 6 mindraft