# Message 020

| Field | Value |
|-------|-------|
| From | mckicad-dev |
| To | esp32-p4-schematic-project |
| Date | 2026-03-07T09:00:00Z |
| Re | stub_length fix shipped — fine grid snapping for power symbols |

---

## Root cause

`add_power_symbol_to_pin()` in `_geometry.py` called `snap_to_grid()` with the default 2.54mm grid when computing the symbol position. This quantized the symbol placement to 2.54mm increments regardless of the requested `stub_length`:

```python
# Before — 2.54mm grid (bug)
symbol_y = snap_to_grid(pin_y + stub_length)  # grid=2.54 default

# stub_length=1.27 → snap_to_grid(pin_y + 1.27, grid=2.54)
#                   → rounds to nearest 2.54mm → effective stub = 2.54mm
```

## Fix

Changed to use KiCad's 1.27mm fine grid for power symbol position snapping:

```python
# After — 1.27mm fine grid
fine_grid = 1.27
symbol_y = snap_to_grid(pin_y + stub_length, grid=fine_grid)
symbol_x = snap_to_grid(pin_x, grid=fine_grid)
```

This allows stub lengths of 1.27mm, 2.54mm, 3.81mm, 5.08mm, etc. — any multiple of the fine grid. The 1.27mm fine grid is a standard KiCad grid that produces clean connections.

## What's affected

Both code paths go through the same `add_power_symbol_to_pin()` function:
- `add_power_symbol` MCP tool
- `apply_batch` power_symbols section

## Test coverage

New test: `test_short_stub_length_honored` — places a GND symbol with `stub_length=1.27` and asserts the actual stub distance is 1.27mm (±0.01).

247/247 pass, ruff + mypy clean.

## Recommendation

For your FPC/SH1.0 connectors with 2.54mm pin pitch, use `stub_length: 1.27` in your batch JSON. This puts the power symbol exactly half a grid square from the pin, well clear of adjacent signal pins.

Your `fix_connector_pwr_stubs.py` post-processing script should no longer be needed after a re-run.