Biome Cleaner

Fixed

• Adjacency mismatch (algorithm-core): Thin-region exploration discovers boundary neighbors via 8-connectivity, but the neighbor-quart lookup only used 4-connectivity. Diagonal-only neighbors were invisible to checkNeighborStability and silently treated as stable, letting a micro biome act as a stable replacement target.
• Depth-limit false STABLE (algorithm-core): When MAX_NEIGHBOR_DEPTH was hit, checkNeighborStability returned STABLE, making a deeply-nested neighbor appear stable. That false STABLE propagated up as a stable neighbor candidate, was selected, and got cached as context-independent -- permanently poisoning the stability cache with wrong replacements.
• Self-reference wins over genuine resolution (algorithm-core): The first unstable neighbor's resolved chain was stored even when it was a cycle-break self-reference. Later neighbors with genuine chain resolutions to the real sink were ignored. Genuine resolutions now upgrade self-referencing results.
• Intermediate boundary biome wins over stable sink (algorithm-core): When a neighbor's chain resolved to another direct boundary biome that was itself being replaced, the algorithm returned it immediately. A chain-follow step now walks the neighborResolution map to reach the terminal sink.
• Biome-type cycle detection false positives (algorithm-core): Cycle detection was keyed by biome type, not region identity. Two disconnected regions of the same biome (e.g., a micro snowy_plains and a large stable snowy_plains) were treated as the same cycle node. Now tracks ancestor region quarts (visitingQuarts) and retries with exclusion when a region-overlap cycle is detected, finding alternative regions of the same biome type.
• Self-ref direct neighbor beats stable neighbor (algorithm-core): A self-referencing direct neighbor (cycle-break survivor that resolves to itself) was preferred over a genuinely stable neighbor. Self-refs are now deprioritized below stable neighbors in the selection ranking.
• Relaxed visiting.contains(resolved) false positive (algorithm-core): Removed the biome-type-only rejection of resolved values matching an ancestor's biome type. The recursive checkNeighborStability already performs region-aware cycle detection, so its result can be trusted even when the resolved biome type appears in the visiting set.
• Conditional breakCycle (algorithm-core): breakCycle now only triggers when the producing chain actually involved cycles (tracked via per-neighbor cycle flags), not when a chain genuinely reached a different region of the target biome type.