test(simulation): Phase-4 hardening — deferred #953/#963 review gaps (T-964)

The verified-still-open coverage list: per-type attractor reachability
fixtures (LakeShore via enclosed depression, PassEntrance via crafted
saddle, PlainCenter via flat terrain, RiverCrossing via confluence) plus
thin_by_spacing behavior (collision, strict-< boundary, equirectangular
column wrap); heightmap 8-bit decode, sea_level passthrough, downsample
identity and zero-target early-return; drainage area_pct bit-for-bit
determinism plus the isolated-basin-fallback divergence comment (Tyre
N1, citing the pre-#953 behavior it deliberately departs from); the
layer1 mountain-branch pairing test (investigated first — the cascade
test supplies a mountain pool but only ever asserted river counts, a
genuine gap); an importer idempotency test covering atlas_city_names
AND atlas_feature_names plus the Sol exemption, wired into
make test-tooling; and the oasis_water dilation radius scaled by
GRID_W/512 (Tyre N2, hash-stable). One stale item dropped per the
refinement trim (test_sim_determinism wiring — already done).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Makefile

@@ -263,6 +263,9 @@ test-tooling:
 	@mkdir -p .cache
 	@python3 tooling/economy-db/test_traits.py 2> .cache/test-tooling-traits.log || \
 		{ echo "  FAIL: traits validation units — log follows:"; cat .cache/test-tooling-traits.log; exit 1; }
+	@echo "  [test-tooling] atlas_city_names/atlas_feature_names idempotency (T-964)..."
+	@python3 tooling/economy-db/test_atlas_idempotency.py 2> .cache/test-tooling-atlas-idempotency.log || \
+		{ echo "  FAIL: atlas name-pool idempotency — log follows:"; cat .cache/test-tooling-atlas-idempotency.log; exit 1; }
 	@echo "  [test-tooling] import_economics --dry-run (committed DB)..."
 	@rc=0; python3 tooling/economy-db/import_economics.py --dry-run \
 		> .cache/test-tooling-dryrun.log 2>&1 || rc=$$?; \