Solar on every roof, BOI solar correction, open source section

Solar (user, 17 Oct 2026: "use as much roof space as possible")
- PV on every roof and canopy: ~640 kWp on the Payap scenario plot
  (factory roof ~523, canopies ~54, flat office roof ~65 kWp around the
  AC units); ~300 kWp on the Mueang Chi hall. Calculator: pvKWp 640,
  new pvSelf 85 % (zero export, hourly sketch), PV cost per kWp times the
  array, office-roof PV in the iso view, roofs drawn full.
- 12.8M to 16.6M THB at 20 to 26 THB/W; CSV baseline 34.37M to 56.34M;
  launch plant ~168M / 231M / 294M THB with contingency; Plan B ~216M
  (label ~215M), ~39M above Plan A; Plan A unchanged (it leases the
  array), its solar lever ~17.5M. PV payback ~4.2 to 5.9 years.
- Permits (rooftop solar no factory licence since 28 Dec 2024, ERC
  exemption under 1,000 kVA, PEA zero export) and PPA discounts sourced
  in sustainability.md.

BOI correction
- Announcement 3/2568 (in force 1 July 2025) ended BOI promotion for
  solar installations; only the battery may qualify (12M THB per MW cap).
  Removed the "BOI solar measure" from boi.md, total-investment,
  revenue-model, sustainability, site-candidates and both plan versions;
  Plan B's case for owning the array is the PPA bill it avoids
  (~0.07M USD a year).

Open source (user, 17 Oct 2026)
- digital-factory.md "Open source throughout, and working with other
  plants": everything we run and build is open source on NixOS, our code
  published (licence to decide), vendor firmware the stated exception;
  later the stack and factory-automation services for other pressing
  plants, not in the revenue.
- Business plan section 5.6 plus an executive-summary bullet, reading
  guide and not-modelled mentions; draft 0.3 rebuilt (A 60, B 61 pages),
  renders re-made with the roofs full.

docs/digital-factory.md

@@ -35,6 +35,50 @@ rows, instrument raw files and images, audio captures. That stays in the
 machine-data store on the plant core, keyed to ERPNext's document names
 ([ERPNext](#erpnext-the-plants-erp)).
 
+## Open source throughout, and working with other plants
+
+Decided (user, 17 October 2026): **everything the plant runs and
+everything we build is open source**, and our own code is published.
+
+| Layer | What runs | Licence |
+|---|---|---|
+| Operating system and deployment | NixOS on every server, gateway, collector and kiosk, declared in the cnx-network clan (clan-core) | nixpkgs: MIT |
+| System of record | ERPNext on the Frappe framework, self-hosted ([ERPNext](#erpnext-the-plants-erp)) | ERPNext: GPLv3; Frappe: MIT |
+| Machine data | PostgreSQL, VictoriaMetrics, Grafana, Mosquitto (MQTT), Telegraf | PostgreSQL licence, Apache-2.0, AGPLv3, EPL-2.0, MIT |
+| Edge and backup | Caddy, BorgBackup, ZFS | Apache-2.0, BSD, CDDL |
+| Our applications | the factory application (`cnx-factory`, Rust: axum, SQLx, minijinja, HTMX), the plant overview, the artist platform (name undecided), the plant and business plan calculator, instrument adapters, NixOS modules | ours, to be published |
+| Design and documents | FreeCAD for the plant model, python-docx and LibreOffice for the business plan | LGPL, MIT, MPL-2.0 |
+
+- **Our licence is a decision point.** AGPL-3.0 keeps hosted copies of the
+  factory application open; Apache-2.0 or MIT is the easiest for another
+  plant to adopt. Decide before the first public release.
+- **The exceptions are inside the machines.** The presses' PLCs and HMIs
+  (Newbilt's Siemens, Pheenix's Beckhoff), the instruments (Keyence, the
+  vision controllers), inverter and battery firmware and the vendors'
+  OPC UA licences are closed. They are appliances: they export data into
+  the NixOS estate and host none of our services. The fleet's access-point
+  controller in the router module is closed too.
+- **What it gives the plant:** no licence fees (ERPNext has no per-seat
+  fee), no vendor lock-in, every machine rebuilt from the repository, and
+  a record a customer can audit (the hash-chained event log).
+
+**Later: a service for other pressing plants.** Once the plant has run
+the stack in production (at least a year), it can be offered to other
+plants around the world:
+
+1. **An open vinyl plant stack**: the NixOS modules, an ERPNext app for
+   pressing (stampers and their genealogy, test pressings, the three
+   gates), the press adapters for Newbilt and Pheenix over OPC UA, S7 or
+   ADS, the kiosk and QC tools.
+2. **Services**: factory automation and data acquisition for another
+   plant (integration and commissioning), remote monitoring and support,
+   hosting of ERPNext and the factory application, training.
+3. **Shared development**: each plant that joins contributes the adapters
+   for its own machines, so the stack covers more presses over time.
+
+None of this is in the business plan's revenue: no price or volume is
+set, and it is an upside like stamper supply to other plants.
+
 ## What the fleet already provides
 
 Read the clan's own runbook (`docs/` in the repo, served on `control`) for