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#architecture

2026-10-07Sentinel: The Command PlaneWhere the system stops observing and becomes able to be wrong in ways that matter: desired and reported held as separate values, a durable claim set, banded arbitration, and a state machine that turns a fire-and-forget write into a verified outcome.23 min
2026-10-05Sentinel Dev Diary: Auditing the WatchdogBuild step four was audited against the watchdog document. One sentence had two halves and a test that asserted the half that worked, three exit criteria passed without a running core anywhere near them, and a stale point's checkpoint never moved until a deployment showed it.13 min
2026-09-30Sentinel: The Watchdog and Derived PointsOne timer wheel for every freshness deadline, why on-change without a heartbeat is a trap, why liveness is a freshness policy rather than a value, and what happens to a derived point whose inputs go stale.17 min
2026-09-28Sentinel Dev Diary: Checks & BalancesFive processes act as checks and balances on the Sentinel build. Code and documents will drift apart on any long project; the aim is to notice quickly and correct it where the next person will see. Here is what each process watches, what keeps it honest, and where it stops.13 min
2026-09-23Sentinel: Ingest Path and Log SchemaTwo logs rather than one, a bus message whose own identity doubles as the dedup key and the ingest watermark, and the native-value column that makes unit conversion reversible - so restart and reprocess both fall out of the schema.20 min
2026-09-21Sentinel Dev Diary: Where the Check LivesThe driver contract says a module emits and says a host reads, and only one of those was built. Three conformance checks placed where one of them can go, a register sentence that was false for three pull requests, and fifty-seven tests that cannot check where a test lives.12 min
2026-09-16Sentinel: The Driver ContractMaking every device look identical to the core while keeping protocol ugliness on the far side of a wire boundary: driver hosts, per-instance supervision, one northbound transport for every protocol, and assignments exported rather than queried.14 min
2026-09-14Sentinel Dev Diary: What the Specification Left UnsaidBuild step one was called complete, then audited against the document that owns it. Six named rejections had become twenty-eight, two of them rules the specification never states, and one guard existed as a function with a fixture and no caller.9 min
2026-09-09Sentinel: The Semantic ModelIdentity, hierarchy and the point descriptor: why a point ID is a dotted slug rather than a UUID, why a component is the unit of independent failure, and why a point is always scalar.17 min
2026-09-08Sentinel Dev Diary: Four Registers and a Drift CheckThe specification was finished before the build started, and then the build began producing statements it had no home for. Four numbered registers, one rule about where a sentence is allowed to live, and the distinction that stops a specification gap being closed by the commit that routed around it.13 min
2026-09-02Sentinel: An IntroductionA soil moisture sensor goes quiet for three days, and nothing in the system says so — a reading and a memory of one look identical. Deciding what that costs is what a specification is for, and this is the first of eleven parts publishing one in full, while the system it describes gets built.20 min
2026-06-30Your CLAUDE.md Is an Architecture Document — Write It Like OneThe patterns worth stealing from a FastAPI project whose agent-instructions file quietly became its architecture doc — layering, config quarantine, the DI trap that breaks transactions, and more.12 min