Terrain distortion when panning or zooming near the edge boundaries of Mercator projection maps

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### mapbox-gl-js version

Mapbox Console

### Browser and version

Brave 1.82.172 (Fingerprint protection disabled) Chromium 140.0.7339.207

### Expected behavior

The terrain should not be distorting/growing/peaking/spiking when moving near the edges of the Mercator projection map, or when zooming in on the terrain.

### Actual behavior

When panning or zooming towards the edges of a Mercator projection map, the 3D terrain becomes distorted.

https://github.com/user-attachments/assets/dfa42af6-de1e-4cd8-b9fe-c7e21a63e2f1

### Link to the demonstration

https://console.mapbox.com/studio

### Steps to trigger the unexpected behavior

Switch projection to Mercator and pan + zoom towards the edge boundaries of the map.

### Relevant log output

```shell

```

Reproduce the issue in the Mapbox Console demonstration by switching to the Mercator projection, then panning and zooming toward the map edges. Trace the terrain rendering path responsible for edge-boundary distortion; done means terrain no longer grows, peaks, spikes, or otherwise distorts near Mercator boundaries.

Written by the indexing model from the issue text.