perf(modeling): O(n²) indexOf + splice in insertTjunctions.js

[jbroll]

Summary

insertTjunctions.js uses indexOf() followed by splice() in loops, causing O(n²) operations.

Usage Frequency: LOW

Only used by generalize() modifier, which is a specialized operation for cleaning up geometry.

Typical model usage: Rare - most models don't use generalize. Used mainly for:

• Cleaning up imported geometry
• Post-processing complex boolean results

Problem

File: packages/modeling/src/operations/modifiers/insertTjunctions.js
Lines: 70-82

idx = vertextag2sidestart.get(starttag).indexOf(sidetag)  // O(n)
if (assert && idx < 0) throw new Error('assert failed')
vertextag2sidestart.get(starttag).splice(idx, 1)  // O(n)

Both indexOf() and splice() are O(n). When called in a loop processing many sides, this becomes O(n²).

Additionally, there's expensive string key generation:

const getTag = (vertex) => \`\${vertex}\`  // Creates string each time
const starttag = getTag(vertex0)
const endtag = getTag(vertex1)
const newsidetag = \`\${starttag}/\${endtag}\`  // More string creation

Suggested Fix

Use a Set instead of array for O(1) operations:

// Instead of array with indexOf/splice:
const sides = new Set()
sides.add(sidetag)
sides.delete(sidetag)  // O(1) instead of O(n)

Impact

Low overall (rare operation), but when generalize is used on complex geometry it can be slow.