Record Accepted PCB Placement And Fit

Align component groups, repair affected routing, and add preservation
audits.
Assign the confirmed U2 footprint and update pull-ups to 2 kΩ across
design files.
Document user acceptance, switch to an A3 worksheet, and refresh PCB
exports.

docs/devel/hardware/PCB/button-notes.md

@@ -1,11 +1,13 @@
 # Button selection: Omron B3F-1000
 
+> **Current status (2026-09-22):** [User acceptance and group alignment](user-acceptance.md) supersedes the earlier pending user-fit, USB-clearance, male-map, procurement and mounting-hardware items below. Original research/evidence remains historical; acceptance is not independent qualification.
+
 Paths in prose point to the retained hardware artifacts or neighboring development notes.
 Commands keep their stated working directory; repository-root paths remain root-relative.
 
 Verified 2026-09-20 against the Omron datasheet and installed KiCad libraries. This research covers three active-low GPIO-to-GND buttons.
 
-**Integration decision:** the A0 schematic now implements B3F-1000 switches with one **2.2 kΩ, 1%, at least 0.125 W external pull-up** per input. The lower-current/internal-pull-up-only discussion below records the selection rationale, not an unselected schematic option. Firmware is unchanged. Exact resistor MPN, supply tolerance/budget and stock remain release checks.
+**Integration decision:** the A0 schematic now implements B3F-1000 switches with one **2 kΩ, 1%, metal-film external pull-up (design rating at least 0.125 W)** per input. The lower-current/internal-pull-up-only discussion below records the selection rationale, not an unselected schematic option. Firmware is unchanged. User reports B3F-1000 and resistors purchased. Exact resistor MPN/wattage and measured supply margin remain unspecified.
 
 ## Schematic-ready recommendation
 
@@ -92,7 +94,7 @@ Inspected `/usr/share/kicad/footprints/Button_Switch_THT.pretty/SW_TH_Tactile_Om
 
 Omron's 10 µA / 1 V minimum is explicitly a **reference value**, not an unconditional low-current reliability guarantee. B3F-1000 is a reasonable prototype choice, but internal-pull-up-only contact reliability should be qualified in the intended environment and over life.
 
-For a conservative silver-contact design within the stated rated load, consider **one external 2.2 kΩ pull-up to 3.3 V per button** (about 1.5 mA while pressed); verify supply/resistor tolerances and GPIO limits before adopting. This recommendation was subsequently adopted in the A0 carrier schematic; see the integration decision above. If low current is important, the datasheet also lists **B3F-1002-G** with gold contacts in the same p. 4 dimensional group, rated 100 µA–50 mA at 3–24 VDC, but with a different operating force (1.76 ±0.49 N); weak internal pull-ups are not automatically within that rated range either. It has not been selected or stock-checked here.
+The original A0 recommendation was 2.2 kΩ (about 1.5 mA); the purchased-part update uses **one external 2 kΩ 1% pull-up to 3.3 V per button** (nominal 1.65 mA while pressed); verify supply/resistor tolerances and GPIO limits before adopting. This recommendation was subsequently adopted in the A0 carrier schematic; see the integration decision above. If low current is important, the datasheet also lists **B3F-1002-G** with gold contacts in the same p. 4 dimensional group, rated 100 µA–50 mA at 3–24 VDC, but with a different operating force (1.76 ±0.49 N); weak internal pull-ups are not automatically within that rated range either. It has not been selected or stock-checked here.
 
 Retain firmware debouncing; a mechanical switch is not bounce-free. The device is unsealed (IP00), and the datasheet prohibits washing.