Three fixes for circular/non-spiral galaxies produced by Randomize:
1. Raise twist range from [1.0, 6.0] to [4.0, 18.0] radians
- Old max (~0.95 turns) could barely curve; new range covers
0.6–2.9 full turns, matching real spiral galaxy morphology
- Default twist raised from 3.0 to 12.0 (~1.9 turns)
2. Scale angular scatter inversely with arm count
- Replaced hardcoded ±0.36 rad scatter with arm_scatter() that
uses 30% of the inter-arm gap (TAU / arms × 0.30)
- Single-arm disks use a generous 1.5 rad scatter
- Prevents high-arm-count disks from blurring into circles
3. Bias randomize_disk toward spiral-friendly values
- Arms weighted toward 2–4 (10%, 30%, 30%, 20%, 10% distribution)
- Twist floored at arms × 4.0 rad so multi-arm disks always wind
enough for distinct spiral structure
- Outer radius defaults to "auto" 60% of the time
francy51
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