Exiting heightmap editor resets manually-set lake types (e.g. lava)

[barrulus]

Found while answering a Discord question about hand-placing lava lakes (research spec: docs/superpowers/specs/2026-08-24-discord-cultures-ice-goods-answer.md).

Symptom

Set a lake's type by hand in the Lakes editor (e.g. freshwater → lava via the type dropdown, src/controllers/lakes-editor.ts:227-243), then open and exit the heightmap editor: the lake snaps back to its computed type.

Cause

The heightmap-editor exit pass reruns Features.defineGroups() (src/controllers/heightmap-editor.ts:645), which recomputes every lake's group from geography (src/generators/features.ts:343,364-391) and overwrites feature.group/feature.subtype. Auto-assignment almost never picks lava (requires height > 60, < 10 cells, firstCell % 10 === 0, features.ts:364-376), so manual lava/frozen/etc. choices are effectively always lost.

This is upstream behavior, not a fork regression. The same wipe-on-regenerate pattern exists for hand-placed ice (Tools → Regenerate ice and heightmap exit both call Ice.generate from scratch — src/components/tools.ts:197-201, heightmap-editor.ts:530,789).

Options

• Document as a known workflow constraint: finish heightmap edits first, retype lakes (and place ice) last.
• Or preserve manual choices: mark a feature as user-typed (e.g. a lock-style flag, as burgs/labels have) and have defineGroups() skip flagged features. Would be upstream-worthy if built.