implemented changes from Jens review

agents.md

@@ -0,0 +1,9 @@
+# Agent Notes — cm4-nrf54
+
+> **Only read the linked files below when they are directly relevant to the current task. Do not load them by default.**
+
+## Available Documentation
+
+| File | When to read |
+|------|-------------|
+| [readme/jlcpcb_parts_check.md](readme/jlcpcb_parts_check.md) | When verifying, auditing, or updating LCSC/JLCPCB part numbers in the schematic |

cm4-nrf54.kicad_prl

@@ -1,6 +1,6 @@
 {
   "board": {
-    "active_layer": 1,
+    "active_layer": 0,
     "active_layer_preset": "",
     "auto_track_width": true,
     "hidden_netclasses": [],
@@ -50,7 +50,7 @@
       "shapes"
     ],
     "visible_layers": "ffffffff_ffffffff_fffffff5_ff5d5fff",
-    "zone_display_mode": 1
+    "zone_display_mode": 0
   },
   "git": {
     "integration_disabled": false,

cm4-nrf54.kicad_pro

@@ -1194,7 +1194,7 @@
       "plot": "",
       "pos_files": "",
       "specctra_dsn": "",
-      "step": "../../../../../../repos/mechanical_beacon/cm4-nrf54_rev3.step",
+      "step": "../../../../../../repos/mechanical_beacon/cm4-nrf54_rev4.step",
       "svg": "",
       "vrml": ""
     },

readme/jlcpcb_parts_check.md

@@ -0,0 +1,104 @@
+# JLCPCB / LCSC Parts Check
+
+How to verify that LCSC part numbers in the schematic match the intended components.
+
+---
+
+## 1. Extract All LCSC Numbers from the Schematic
+
+Use the following Python snippet to parse `cm4-nrf54.kicad_sch` and dump all component references with their value and LCSC field:
+
+```python
+import re
+
+with open('cm4-nrf54.kicad_sch', 'r') as f:
+    content = f.read()
+
+lcsc_pattern = re.compile(r'\(property\s*"(?:LCSC|lcsc|LCSC Part)"\s*"([^"]+)"')
+field_pattern = re.compile(r'\(property\s*"(LCSC|lcsc|LCSC Part)"\s*"([^"]+)"')
+
+blocks = re.split(r'\n\s*\(symbol\s+\(lib_id', content)
+
+results = []
+for block in blocks[1:]:
+    ref_m  = re.search(r'\(property\s*"Reference"\s*"([^"]+)"', block)
+    val_m  = re.search(r'\(property\s*"Value"\s*"([^"]+)"', block)
+    lcsc_m = lcsc_pattern.search(block)
+    field_m = field_pattern.search(block)
+
+    ref   = ref_m.group(1)  if ref_m  else '?'
+    val   = val_m.group(1)  if val_m  else '?'
+    lcsc  = lcsc_m.group(1) if lcsc_m else ''
+    field = field_m.group(1) if field_m else ''
+
+    if ref.startswith('#') or ref == '?':
+        continue
+    results.append((ref, val, lcsc, field))
+
+results.sort(key=lambda x: (
+    ''.join(filter(str.isalpha, x[0])),
+    int(''.join(filter(str.isdigit, x[0])) or '0')
+))
+
+for ref, val, lcsc, field in results:
+    print(f'{ref:12} {val:42} {lcsc:15} {field}')
+```
+
+> **Note:** KiCad schematics use three different field names for the LCSC number:
+> `LCSC`, `lcsc`, and `LCSC Part` — the script above catches all three.
+
+---
+
+## 2. Verify Each LCSC Number
+
+For each non-trivial component, open the LCSC product page directly:
+
+```
+https://www.lcsc.com/product-detail/C<NUMBER>.html
+```
+
+The page title shows the actual manufacturer part number. Cross-check against the schematic `Value` field.
+
+### What to look for
+
+- **Wrong part** — the LCSC number resolves to a completely different component (e.g. a 22Ω resistor assigned to a 220R position, or an ADC with the wrong channel count).
+- **Package mismatch** — the part is the right IC but in a different package than the KiCad footprint (e.g. SOT-363 assigned to a SOT-23-5 footprint).
+- **Wrong variant** — same family but different spec (e.g. PCM1862 vs PCM1863, which differ in channel count).
+- **Part not found** — the LCSC number returns a 404 / "Page Not Found". The part may be new, discontinued, or the number is a typo.
+- **Missing LCSC** — component has no LCSC field at all. If it is a real assembly part (not a mechanical hole, test point, or solder jumper), it needs one.
+
+---
+
+## 3. Check JLCPCB Assembly Availability
+
+Not all LCSC parts can be assembled by JLCPCB. To check:
+
+```
+https://jlcpcb.com/partdetail/<MANUFACTURER>-<PART>/C<NUMBER>
+```
+
+Or search directly at `https://jlcpcb.com/parts`.
+
+### Stock status meanings
+
+| Status | Meaning |
+|--------|---------|
+| **In-stock, qty shown** | Orderable, JLCPCB can assemble |
+| **C9900xxxxxx** number | Consigned part — you must supply the component |
+| *"unavailable for purchase but can still be used in assembly"* | Must be consigned; cannot be bought through JLCPCB |
+
+---
+
+## 4. Finding Alternatives
+
+When a part is not available on LCSC/JLCPCB, search for drop-in alternatives:
+
+- Search `site:lcsc.com <part number>` or `site:jlcpcb.com <part number>`
+- Check the Raspberry Pi / EasyEDA forums for CM4-specific parts (e.g. RJ45 MagJack alternatives)
+- Common compatible replacements for this project:
+
+| Original | Alternative | LCSC | Notes |
+|----------|-------------|------|-------|
+| Bel Fuse A70-112-331N126 (MagJack) | LINK-PP LPJG0926HENL | **C22457393** | Pin-compatible, 387 pcs in stock at JLCPCB |
+
+---

scripts/extract_lcsc.py

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+#!/usr/bin/env python3
+"""Extract all LCSC part numbers from a KiCad schematic and print a sorted table."""
+
+import re
+import sys
+
+SCH_FILE = 'cm4-nrf54.kicad_sch'
+
+if len(sys.argv) > 1:
+    SCH_FILE = sys.argv[1]
+
+with open(SCH_FILE, 'r') as f:
+    content = f.read()
+
+lcsc_pattern = re.compile(r'\(property\s*"(?:LCSC|lcsc|LCSC Part)"\s*"([^"]+)"')
+field_pattern = re.compile(r'\(property\s*"(LCSC|lcsc|LCSC Part)"\s*"([^"]+)"')
+
+blocks = re.split(r'\n\s*\(symbol\s+\(lib_id', content)
+
+dnp_pattern = re.compile(r'\(dnp\s+yes\)')
+
+results = []
+for block in blocks[1:]:
+    ref_m   = re.search(r'\(property\s*"Reference"\s*"([^"]+)"', block)
+    val_m   = re.search(r'\(property\s*"Value"\s*"([^"]+)"', block)
+    lcsc_m  = lcsc_pattern.search(block)
+    field_m = field_pattern.search(block)
+
+    ref   = ref_m.group(1)   if ref_m   else '?'
+    val   = val_m.group(1)   if val_m   else '?'
+    lcsc  = lcsc_m.group(1)  if lcsc_m  else ''
+    field = field_m.group(1) if field_m else ''
+    dnp   = bool(dnp_pattern.search(block))
+
+    if ref.startswith('#') or ref == '?':
+        continue
+    results.append((ref, val, lcsc, field, dnp))
+
+def sort_key(x):
+    letters = ''.join(filter(str.isalpha, x[0]))
+    digits  = ''.join(filter(str.isdigit, x[0]))
+    return (letters, int(digits) if digits else 0)
+
+results.sort(key=sort_key)
+
+print(f'{"REF":12} {"VALUE":42} {"LCSC":15} {"DNP":3} FIELD')
+print('-' * 87)
+for ref, val, lcsc, field, dnp in results:
+    dnp_str = 'DNP' if dnp else '   '
+    skip = dnp or ref.startswith(('H', 'JP', 'TP'))
+    flag = '  <-- MISSING' if not lcsc and not skip else ''
+    print(f'{ref:12} {val:42} {lcsc:15} {dnp_str} {field}{flag}')