Software: pattern player, web page with a design library, GRBL tools

- python3 -m sandtable web: local web page to play designs from a library of
  27 built-in patterns, upload .thr or .svg, pause/skip/stop, jog and calibrate.
  Reconnects by itself when the USB cable comes back.
- Plays .thr files and built-in generators with an erase spiral between them,
  constant ball speed, host-side homing on stock GRBL 1.1 (Uno + CNC shield),
  FluidNC for the ESP32 board.
- Home switch guard: patterns never press the switch, so a press means lost
  steps and stops the machine at once with an alert.
- lineart.py turns SVG line drawings into one continuous path.
- Tests against a GRBL simulator.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

software/sandtable/thr.py

@@ -0,0 +1,50 @@
+"""Read and write .thr (theta-rho) pattern files.
+
+Each line holds "<theta> <rho>":
+  theta: angle in radians, continuous (it keeps counting past 2*pi; it is not wrapped)
+  rho:   distance from the centre, 0 (centre) to 1 (edge)
+Lines starting with '#' or '//' are comments. This is the format used by Sandify,
+Sisyphus and Dune Weaver.
+"""
+import math
+
+Pattern = list  # list of (theta_rad, rho) tuples
+
+
+def loads(text):
+    pts = []
+    for raw in text.splitlines():
+        line = raw.strip()
+        if not line or line.startswith('#') or line.startswith('//'):
+            continue
+        parts = line.replace(',', ' ').split()
+        if len(parts) < 2:
+            continue
+        try:
+            th, rho = float(parts[0]), float(parts[1])
+        except ValueError:
+            continue
+        if math.isfinite(th) and math.isfinite(rho):
+            pts.append((th, min(1.0, max(0.0, rho))))
+    return pts
+
+
+def load(path):
+    with open(path, encoding='utf-8', errors='replace') as f:
+        pts = loads(f.read())
+    if len(pts) < 2:
+        raise ValueError(f'{path}: no theta-rho points found')
+    return pts
+
+
+def dumps(pts, header=None):
+    out = []
+    if header:
+        out += [f'# {h}' for h in header.splitlines()]
+    out += [f'{th:.5f} {rho:.5f}' for th, rho in pts]
+    return '\n'.join(out) + '\n'
+
+
+def save(path, pts, header=None):
+    with open(path, 'w') as f:
+        f.write(dumps(pts, header))