Stamped technical decisions

The decision board for the technical architecture. Moved out of architecture section 9 on 7 October 2026 so the architecture states what is built and planned, and this file holds what is still to be decided. Internal. Nothing here claims a result at a plant; verified savings are ₹0. The master document hard stops bind every option below.

Waiting on Vinayak#

Each of these is RECOMMENDED — awaiting Vinayak. The architecture follows the recommendation until Vinayak decides; every entry below says how to reverse it.

• D1 — Plant context store. Relational plus event tables in L2, link method and confidence on every edge.
• D2 — Contracts. Draft all ten in SE now as 0.x, experimental, bump on first plant use.
• D3 — Twin runtime. Python on the Plant Box behind a heartbeat gate; compiled core only if the gate fails.
• D4 — Plant Box. Fanless industrial PC on Linux; customer VM as fallback.
• D5 — Value method. Switchback where actions alternate, adjusted baseline otherwise, power analysis first.
• D6 — MSPC and soft sensors. L3, KR analytics moved alongside.
• D7 — Fast-loop channel. WhatsApp plus a local Plant Box display.
• D8 — Time-series foundation models. Shadow-only until a held-out win.
• D9 — Model registry. L3 registry is the single owner; EV becomes a library.
• D10 — Writer protocol. OPC UA write only.
• D11 — TabPFN pin. Pin to a release whose default weights are v2.
• D12 — Client numbers. Script-and-commit rule.
• D15 — Safety filter owner. One filter in the L5 autonomy package, run as edge and cloud copies.
• D16 — Message budgets. Extend L5.
• D17 — NE 178 depth. Pattern-level Verification of Request.
• D20 — L2 hosting. Self-managed Postgres + Timescale on EC2 until 10 plants, then Tiger Cloud.
• D21 — LLM provider and data residency. One gateway, low-cost default model, no plant data to a provider the customer has not approved.

Deferred: D18 (probabilistic stack): choose PyMC, NumPyro or Stan with the first C15 template.

Decided by Vinayak (7 Oct 2026): D13 (Evidence labels), D14 (Calibration thresholds), D19 (MHE solver). The architecture states these as facts.

How to read an entry#

Each decision has a status, the recommendation, the options and trade-offs considered, the evidence, how to reverse it, and what it blocks. D13, D14 and D19 are DECIDED by Vinayak (7 Oct 2026) and D18 is DEFERRED; every other entry is RECOMMENDED and waits for Vinayak. D1–D5 block the most downstream work; D3, D4, D10, D15 and D17 sit on the closed-loop critical path. D20 and D21 were added while finalising: D20 because Amazon RDS does not offer the TimescaleDB extension L2 needs, D21 because data residency decides which LLM a customer will accept.

Section marks (section ) in the entries refer to the architecture. C-numbers are capabilities and E- and I-numbers are evidence, defined in the capability map and the evidence ledger.