test(gate): stress repro judges terrain penetration -- gate on 10/10 clear, gate off 3/3 falls through

The old criteria (travel distance) could not tell a working gate from a broken one: every run,
gate on or off, ended at (455.7, 0, -58.1). That spot is measured air ~1.2 m above a real floor
(density zero-crossing at world Z ~ -275.7 cm), so it is a terrain trap, not a fall-through.

The stress test now drops the pawn fast onto an unready support tile (0,0,-1) and samples the
density at the capsule feet every frame, sweeping at <= half a voxel between positions. PASS =
no measured clearance below -5 cm.

Owner config (radius 3, max level 6, distance 768, sheets off):
- gate on: 10/10 PASS, min clearance +120.5..+120.9 cm, one hold of 0.43-0.47 s each,
  support submitted in ~0.7 ms, collision ready in 0.43-0.47 s
- gate off: 3/3 FAIL terrain_penetration, clearance -5.7..-8.1 cm
Edit-ghost, clipmap no-overlap sweep: pass. Test-harness code only; no production path changed.
This validates a49725d.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Tools/VoxelForgeTest.ps1

@@ -994,7 +994,12 @@ function Get-CollisionGateStressMetrics([string]$LogPath) {
                         'gate_holds', 'gate_total_s', 'max_gate_s', 'full_stops',
                         'full_stop_total_s', 'collision_gate', 'gate_progress_m', 'support_tile',
                         'support_first_check_to_submit_s',
-                        'support_first_check_to_collision_ready_s')) {
+                        'support_first_check_to_collision_ready_s', 'test_support_tile',
+                        'test_support_first_check_to_submit_s',
+                        'test_support_first_check_to_collision_ready_s', 'landed', 'terrain_samples',
+                        'terrain_measurement_missing', 'start_height_crossed',
+                        'min_clearance_cm', 'min_clearance_position', 'min_feet_density',
+                        'min_surface_vox_z', 'final_position')) {
         $match = [regex]::Match($line, ('{0}=(?<v>[^ ]+)' -f $key))
         if ($match.Success) { $metrics[$key] = $match.Groups['v'].Value }
     }
@@ -1451,7 +1456,6 @@ try {
         'gate-stress' {
             $baseCvars['voxel.TestCollisionGateStress'] = 1
             $baseCvars['voxel.TestCollisionGateStressSpeedCmPerSecond'] = 6000
-            $baseCvars['voxel.TestCollisionGateStressStartDelaySeconds'] = 0.1
             $baseCvars['voxel.TestCollisionGateStressDurationSeconds'] = 2
             $baseCvars['voxel.TestCollisionGateStressTimeoutSeconds'] = 30
             $args = New-CommonArguments 'game' (Join-Path $RunRoot 'Logs\gate-stress.log') (Merge-Cvars $baseCvars)
@@ -1506,7 +1510,6 @@ try {
             $stressBaseCvars = [ordered]@{
                 'voxel.TestCollisionGateStress' = 1
                 'voxel.TestCollisionGateStressSpeedCmPerSecond' = 6000
-                'voxel.TestCollisionGateStressStartDelaySeconds' = 0.1
                 'voxel.TestCollisionGateStressDurationSeconds' = 2
                 'voxel.TestCollisionGateStressTimeoutSeconds' = 30
             }