Reduce GPU load of selection scan

[nabeya11]

Problem

scanSelection runs a transform-feedback pass over all points and reads the result back from the GPU on every click, Delete, label key, and console command. On large clouds this wait occurs on every operation. In addition, the Alt/Ctrl click paths ran the same scan twice.

Changes

• Cache the scan result. The scan output depends only on the point cloud, the crop/select/view/projection matrices, and the cursor position, so the scan is skipped while none of them change. Matrices are compared by value; the cloud and the mask are tracked by new revision counters (updates are funneled through setPointCloudUpdated() to prevent missed invalidations). Only the click path uses the cursor-dependent bit, so it alone requires an exact (x, y) match (needNearCursor).
• Remove the duplicated scan on Alt/Ctrl click. The result of the scan at the beginning of the click handler is still valid there.
• Poll the GPU fence with exponential backoff (1→2→…→10ms) instead of the previous flat 10ms interval.

A missed invalidation would silently apply an edit with a stale selection, so the cache can be disabled at runtime with the new scan_cache 0 console command.

[codecov]

Codecov Report

❌ Patch coverage is 76.74419% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 39.91%. Comparing base (009b647) to head (5b4ca1e).

Files with missing lines	Patch %	Lines
command.go	74.19%	8 Missing ⚠️
console.go	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #356      +/-   ##
==========================================
+ Coverage   38.96%   39.91%   +0.94%     
==========================================
  Files           8        8              
  Lines        1414     1443      +29     
==========================================
+ Hits          551      576      +25     
- Misses        827      831       +4     
  Partials       36       36              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Copilot]

Pull request overview

This PR reduces the latency and GPU/CPU overhead of selection-related operations by avoiding redundant selection scans, reusing prior scan results when inputs are unchanged, and improving GPU fence polling behavior.

Changes:

• Adds a selection scan cache keyed by cursor position (when needed), relevant matrices, and new revision counters for point cloud / selection-mask state.
• Removes a duplicated selection scan in the Alt/Ctrl click paths by reusing the click’s initial scan result.
• Changes GPU fence polling to use exponential backoff instead of a fixed sleep interval.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
main_js.go	Adds scan-result caching, removes duplicate scan on Alt/Ctrl click, and updates fence polling behavior.
console.go	Adds a scan_cache console command to toggle the scan cache at runtime.
command.go	Introduces revision counters and cache-enable state to support reliable scan-cache invalidation.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

Suppressed comments (1)

command.go:680

• Undo() bumps pointCloudRev (via setPointCloudUpdated()) even when there is nothing to undo. This unnecessarily invalidates the selection-scan cache and forces point cloud re-uploads/rerenders despite no state change. Bump the revision only when editor.Undo() actually succeeds.

func (c *commandContext) Undo() bool {
	c.setPointCloudUpdated()
	return c.editor.Undo()
}