Give a place the geohash cell that contains its own centroid

CHANGELOG

@@ -1,13 +1,51 @@
 ### Unreleased
 
+- Give every place the geohash cell that contains its own centroid, ahead of
+  the population tie-break, so a border town no longer loses its own centre to
+  the larger city across the border (for example Calexico resolving to
+  Mexicali, or Heerlen to Aachen). Placetype ranking is unchanged, and cells
+  holding two centroids are still decided by population. Disable with
+  `--home-cell-priority false` (`WOF_HOME_CELL_PRIORITY=0`). Centroid
+  coordinates outside the place geometry, including an exterior bounding-box
+  midpoint fallback, do not receive home-cell priority.
+- Stop the dominant-city rollup absorbing the home cell of a town in another
+  country, whether that cell is a descendant of the promoted parent or the
+  promoted parent itself. Rollups inside a country are unchanged, so a metro
+  still reads as one city.
+- Apply home-cell ownership across nested cover cells, not only within a single
+  hash. A place that owns the coarse cell holding its centroid now also keeps
+  the finer cells over that same point when a neighbour emits them, so the rule
+  holds for the longest-prefix lookup the runtime actually performs. Placetype
+  ranking still decides first, and no cell is added to the index.
+- By default, stop the dominant-city rollup suppressing or replacing a place
+  whose placetype it does not outrank, whether that place owns a descendant cell
+  or the promoted parent itself. A county could absorb the cell holding a town's
+  own centre, which is a downgrade the cell comparator would never make - and
+  because the rollup runs per batch, it left that cell undefended in an
+  `--append` build, so the next country written took it and the town's centre
+  resolved across the border (Douglas AZ reading as Agua Prieta; Mittelberg and
+  Riezlern, the Austrian Kleinwalsertal, reading as Oberstdorf). Rollups between
+  localities are unchanged; explicitly adding `county` to
+  `--dominant-city-placetypes` restores the earlier county suppression behavior.
+- Judge compact-index redundancy against the nearest kept ancestor cell instead
+  of any matching prefix. A row was dropped whenever some coarser cell named the
+  same place, even when a different place owned the cell in between, and the
+  lookup then answered with that other place.
+- Reconcile nested home cells from each place's own cover rather than from the
+  cells it happened to win, so a place that loses the cell holding its centroid
+  to a co-centred neighbour still carries its claim to the finer cells over that
+  point. The pass no longer depends on the order places are read.
+- Report the rollup and home-cell invariants in the build summary (promotions
+  refused, home cells reclaimed or kept, rows kept from a shadowing owner), so a
+  world build shows whether any of these rules ever fires.
 - Keep counties out of the dominant-city rollup. A parent geohash cell rolled
   up to the place that dominates its children on population, and `county`
   counted as a city-like placetype, so a metro could be labelled with its
   county's name while the smaller localities under it lost their own cells
   (Brockport and Greece, NY answering "Monroe"). The rollup now only hands a
   parent cell to a placetype listed in `--dominant-city-placetypes`
   (default `locality,localadmin`, env `WOF_DOMINANT_CITY_PLACETYPES`); add
-  `county` to that list to reproduce earlier builds. Counties still win cells
+  `county` to restore county eligibility. Counties still win cells
   through the normal comparator. Both routes into a parent cell -- winning the
   dominant-city competition, and being the only city-like owner in the cell --
   share one eligibility gate, so a county cannot take a parent cell through the

README.md

@@ -239,10 +239,12 @@ Builder notes:
   - `--region-max-precision`
   - `--region-sparse-max-precision` + `--region-sparse-min-area-km2` for very large sparse regions (for example geohash-3 in Amazon-like interiors)
 - `--promote-locality-over-region` (default `true`) prefers locality labels in shared parent cells when there is no competing locality (keeps city labels sticky against region-only outskirts)
+- `--home-cell-priority` (default `true`) gives a place the cell that contains its own centroid, ahead of the population tie-break, so a border town is not swallowed by the larger city across the border. Placetype ranking still applies first, and a cell holding two centroids is still decided by population. A centroid coordinate outside the place geometry does not receive this priority; this includes bounding-box midpoint fallbacks that land outside concave, holed, or multipart geometry. Because the index is walked by longest matching prefix, the claim is enforced across nested cells too: a place that owns the coarse cell holding its centroid also keeps the finer cells over that point. The dominant-city rollup keeps a foreign town's home cell for the same reason, whether that cell is the promoted parent or one of its descendants; rollups within one country are unaffected. This is a guarantee of the generated, uncurated database; an explicitly applied [curation overlay](curation/README.md) is the final labeling layer and may deliberately reassign matching cells, including an absorbed place's home cell
 - Dominant-city rollup keeps broad city labels sticky in mixed city/suburb cells unless there is competing major-city pressure:
   - `--dominant-locality-population` (default `100000`)
   - `--dominant-locality-ratio` (default `3`)
-  - `--dominant-city-placetypes` (default `locality,localadmin`) placetypes eligible to be the dominant city of a parent cell, whether it wins a competition or is the only city-like owner in that cell. A county wins cells like any other place, but naming a whole parent cell after it reads as a mistake, so it is excluded by default; add `county` to reproduce pre-1.1 builds
+  - `--dominant-city-placetypes` (default `locality,localadmin`) lists placetypes eligible to be the dominant city of a parent cell, whether one wins a competition or is the only city-like owner in that cell. A county still wins cells on its own merits but is excluded from naming a whole parent cell by default; explicitly adding `county` restores the earlier county rollup, including suppression of lower-ranked locality descendants
+  - Without that explicit county override, a rollup only folds a place into a better- or equally-ranked label, so a county cannot absorb a locality and strip the town of the cell holding its own centre
 - Parent-cell takeover guard:
   - `--parent-locality-min-share` (default `0.5`) requires locality ownership of at least that child-cell share before replacing a parent cell label
 - Excludes neighbourhood-like placetypes from default reverse output
@@ -281,6 +283,7 @@ Useful WOF build env vars:
 - `WOF_REGION_SPARSE_MAX_PRECISION` sparse very-large-region precision (default `3`)
 - `WOF_REGION_SPARSE_MIN_AREA_KM2` area threshold for sparse region precision (default `80000`)
 - `WOF_PROMOTE_LOCALITY_OVER_REGION=1|0` prefer locality labels over region in shared parent cells (default `1`)
+- `WOF_HOME_CELL_PRIORITY=1|0` let a place keep the cell that contains its own centroid (default `1`)
 - `WOF_DOMINANT_LOCALITY_POPULATION` major-locality threshold for dominant-city rollup (default `100000`)
 - `WOF_DOMINANT_LOCALITY_RATIO` dominant-vs-next locality population ratio (default `3`)
 - `WOF_DOMINANT_CITY_PLACETYPES` placetypes eligible to be a parent cell's dominant city (default `locality,localadmin`)