docs: reconcile BOM + Build Guide with v1.2.1 hardware (items 1,2,5,7)

- Zip tie: BOM 1 -> 4, with the breakdown in Description (1 motor-side elbow,
  1 far-side pulley, 2 ring-curtain carriages) so it matches the wiki's 4.
- Version: BOM header "v1.1" -> current "v1.2.1"; wiki "New in v1.1" banner ->
  "Current hardware - v1.2.1" and its print-path link fixed
  (hardware/plastics/v1.1 was a broken path; the folder is v1.2.1).
- Foam mounting row: "Foam mounting squares (set of 5) | 5" was ambiguous
  (5 sets vs 5 squares) -> "Foam mounting square, 1\" | 5" + "five squares per
  unit", in both files.
- Carriages: added a note to both files stating the standard build uses two
  carriages, with a TODO for how the count scales with panel count (no rule is
  documented in the repo, so none was invented).

Items 3/4/6 are report-only or blocked on a question (see PR description) and are
NOT changed here.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: daniel-frenkel

docs/BOM-V2.0.md

@@ -1,6 +1,6 @@
 # BOM V2.0
 
-> Reflects the **v1.1** hardware. What changed from v1.0: a smaller-diameter **MK8** drive gear (pull strength 11 lb → 15 lb), **one larger 633ZZ bearing per arm** instead of two small bearings, and **pre-cut PTFE tubes** (no razor-cutting). Quantities are per unit. Every purchasable part links to the [Valar Systems store](https://valarsystems.com).
+> Reflects the current **v1.2.1** hardware. Notable changes since v1.0: a smaller-diameter **MK8** drive gear (pull strength 11 lb → 15 lb), **one larger 633ZZ bearing per arm** instead of two small bearings, **pre-cut PTFE tubes** (no razor-cutting), **foam mounting squares** in place of adhesive command strips, and a **24 V 1.5 A** power adapter. Quantities are per unit. Every purchasable part links to the [Valar Systems store](https://valarsystems.com).
 
 ## Body Assembly
 
@@ -25,15 +25,17 @@
 | PTFE tubing, 3 mm ID × 5 mm OD (pre-cut) | 6 | 2 × 10 mm, 2 × 40 mm, 2 × 70 mm — [buy](https://valarsystems.com/products/ptfe-tube). |
 | M3 × 10 mm screw, self-tapping | 14 | [Thread-forming screw](https://valarsystems.com/products/m3-x-10mm-thread-forming-screw). |
 | M3 square nut | 1 | [Curtain-pulley nut](https://valarsystems.com/products/m3-square-nut). |
-| Zip tie | 1 | Small, 2–3 mm wide — [buy](https://valarsystems.com/products/zip-tie). |
+| Zip tie | 4 | Small, 2–3 mm wide. One for the motor-side rope elbow, one for the far-side pulley, and two for attaching carriages to ring curtains (one per carriage) — [buy](https://valarsystems.com/products/zip-tie). |
 | V623ZZ pulley | 1 | 3 × 12 × 4 mm — [V-groove pulley](https://valarsystems.com/products/v-groove-pulley). |
 | Rope | 1 | 1.6 mm diameter — [buy](https://valarsystems.com/products/rope). |
 
+> **Carriages:** the standard build uses **two** carriages (one with a single top screw, one with two). How many carriages a multi-panel curtain needs is not documented yet — **TODO**.
+
 ### Mounting Hardware
 
 | Part | Qty | Description |
 | :--- | :---: | :--- |
-| Foam mounting squares (set of 5) | 5 | 1" square double-sided foam. Wipe the surface clean and dry, then press firmly — [buy](https://valarsystems.com/products/foam-mounting-squares). |
+| Foam mounting square, 1" | 5 | Double-sided; **five squares per unit**. Wipe the surface clean and dry, then press firmly — [buy](https://valarsystems.com/products/foam-mounting-squares). |
 
 ## Assembly Tools Required
 

docs/wiki-Build-Guide.md

@@ -6,12 +6,12 @@
 
 Assembling a Ropener takes about **20 minutes** with three common hand tools — no soldering. It comes together in three stages: the **motor body**, the **curtain-rail carriages**, and **attaching it to your curtains**. Follow whichever guide below suits you — they all cover the same build.
 
-> 🆕 **New in v1.1** — This guide covers the current **v1.1** hardware:
+> 🆕 **Current hardware — v1.2.1.** Notable changes since v1.0:
 > - **Stronger pull (11 lb → 15 lb)** from a smaller-diameter **MK8** drive gear (replaces the MK7).
 > - **One larger 633ZZ bearing (3 × 13 × 5 mm) per arm** instead of two small bearings.
 > - **Pre-cut PTFE tubes** (10 / 40 / 70 mm) — no measuring or razor-cutting.
 >
-> Print from [`hardware/plastics/v1.1`](https://github.com/Valar-Systems/Ropener/tree/main/hardware/plastics/v1.1). The v1.0 files remain in the repo for anyone who already built one.
+> Print from [`hardware/plastics/v1.2.1`](https://github.com/Valar-Systems/Ropener/tree/main/hardware/plastics/v1.2.1). Earlier revisions remain in the repo for anyone who already built one.
 
 ## How to build
 
@@ -87,7 +87,7 @@ Everything the build needs is below. For the full, maintained list see the [Bill
 | NEMA 17 stepper motor | 1 |
 | 24 V 1.5 A power adapter | 1 |
 | Cable extension | as needed |
-| Foam mounting squares (set of 5) | 5 |
+| Foam mounting square, 1" | 5 |
 | 1.6 mm rope | 30 ft |
 | PTFE tubing (pre-cut: 2 × 10 mm, 2 × 40 mm, 2 × 70 mm) | 6 |
 | M3 square nut | 4 |
@@ -154,6 +154,8 @@ This device works on the following curtain types.
 
 > **Overview.** Along the rod, from one end to the other, you'll have: the **pulley**, a **carriage with one screw on top**, a **carriage with two screws on top**, and the **motor-side** anchor.
 
+> **How many carriages?** The standard build uses **two** (one single-screw, one double-screw). How carriage count should scale as the number of curtain panels grows is not documented yet — **TODO**.
+
 <!-- 📷 media/build-guide/15-setup-overview.png — rail layout: pulley, 1-screw carriage, 2-screw carriage, motor side -->
 
 The **PTFE tubes come pre-cut** — no cutting needed. You'll have **two of each length**: