BOI: machinery import duty and import VAT, PVC duty relief

User, October 2026: take the BOI duty-free import and VAT exemption into
consideration.

- boi.md: import VAT goes with the BOI duty exemption (Revenue Department
  answer on the BOI OSOS FAQ, checked October 2026); what it is worth:
  ~2.75M USD of imported machinery at the start fleet (block midpoints)
  would otherwise carry ~5 % duty (Thai MFN averages 4.1 % on HS 8477,
  0 to 10 % across HS 84; estimate until the HS codes are set), ~0.14M
  USD, and 7 % import VAT, ~0.2M paid at the border and recovered later
  as input tax, mostly as a refund claim since exports are zero-rated.
- total-investment.md: the blocks are vendor prices without duty or
  import VAT, so the headline already assumes promotion.
- Fleet calculator: BOI promoted / not promoted switch and export share.
  Not promoted adds the machinery duty to capex and depreciation, shows the
  import VAT as cash at the border, and charges duty on imported PVC
  compound; promoted exempts both, with no compound duty on exported
  records and 90 % off for domestic sales (sections 36(1) and 30). A note
  under the KPIs shows what promotion saves either way. Defaults: payback
  3.1 years with BOI, 3.2 without; adverse case operating result -31k
  with BOI, -68k without. CIT and BOI CIT exemptions still not modelled.

docs/boi.md

@@ -39,7 +39,22 @@ not on "we press plastic discs."
 ## What Group B still delivers (the core value)
 
 - **Machinery import duty exemption**: significant with the entire equipment
-  list imported (Germany, Sweden, USA, Japan)
+  list imported (Germany, Sweden, USA, Japan). **Import VAT goes with it:**
+  machinery or raw material imported with the duty exemption is exempt
+  from VAT at import as well (Revenue Department answer on the
+  [BOI OSOS FAQ](https://osos.boi.go.th/One-Stop/faq-group/205/FAQ-about-VAT--BOI),
+  checked October 2026); otherwise a BOI company is treated like any other
+  for VAT. What it is worth: the capex blocks in
+  [total investment](finance/total-investment.md) are vendor prices
+  without duty or VAT, so they already assume promotion. Without it, the
+  ~2.75M USD of imported machinery at the start fleet (presses, galvanics,
+  Sibert, lathe system, metrology; block midpoints) would carry import duty,
+  roughly 5 % (Thailand's MFN averages 4.1 % on HS 8477 plastics
+  machinery, 0 to 10 % across HS 84; estimate until the HS codes are set),
+  ~0.14M USD, and 7 % import VAT, ~0.2M USD paid at the border and only
+  recovered later as input tax, mostly as a refund claim because exports
+  are zero-rated. The [press fleet calculator](fleet-calculator.html)
+  shows both cases.
 - **100% foreign ownership** of the promoted manufacturing company,
   overriding Foreign Business Act restrictions for the promoted activity
 - **Land ownership** for the promoted operation despite foreign