# Additional-generation geography integrity fixes

## Fixed issues

1. **Multiple prefectural capitals in one prefecture**
   - Re-normalizes capital flags against the final prefecture raster after patch merge.
   - Keeps at most one capital-like city per prefecture, preferring established capitals.

2. **Selection dotted outline could not be cleared**
   - Added a `Clear Selection` button.
   - `Escape` also clears the active patch selection when generation is idle.

3. **Rivers appearing over sea**
   - Final river raster is clipped against the final sea mask.
   - River path layers are split/removed where path points fall on final sea cells.

4. **Extremely small generated prefectures**
   - Newly generated prefectures are no longer immune to administrative cleanup.
   - Tiny newly allocated prefectures are merged into the strongest adjacent prefecture.
   - Established pre-existing prefectures are never collapsed by this cleanup.

5. **Unnatural geography along generation boundaries**
   - Added old/new terrain-frontier harmonization while keeping the established side fixed.
   - Added administrative-frontier continuation so municipality/prefecture borders do not terminate on the generation edge.
   - Increased expansion overlap and corner taper to avoid rectangular/clipped coastlines and terrain.
   - Added a final footprint restore so derived-field recomputation cannot leak outside the irregular generated footprint.

## Regression validation

`VALIDATE_REPORTED_PATCH_BUGS.mjs` checks the five reported failure classes directly.

Final observed result:

- river points on sea: `0`
- prefectures with duplicate capitals: `0`
- tiny generated prefectures in probe: `0`
- municipality breaks on established generation frontier: `0`
- prefecture breaks on established generation frontier: `0`
- maximum established-frontier elevation jump: `0.0383`
- seam status: `clean`

Existing `STEP17_VALIDATION.mjs` also passes with `ok: true`, preserving alternative-generation differentiation, explicit render revision, and single-patch Worker lifetime behavior.