diff --git a/tests/testHeaderCoexistence.cpp b/tests/testHeaderCoexistence.cpp
index ac98c00..47bd998 100644
--- a/tests/testHeaderCoexistence.cpp
+++ b/tests/testHeaderCoexistence.cpp
@@ -152,3 +152,118 @@ VF_TEST(everyPublicHeaderIsListedInTheCoexistenceGuard) {
     }
     CHECK(onDisk.size() > 60u);
 
+    std::set<std::string> included;
+    std::ifstream source(root / "tests" / "testHeaderCoexistence.cpp");
+    CHECK(source.good());
+    const std::string prefix = "#include \"vf/";
+    std::string line;
+    while (std::getline(source, line)) {
+        if (line.rfind(prefix, 0) != 0) continue;
+        std::size_t end = line.find('"', prefix.size());
+        if (end == std::string::npos) continue;
+        included.insert(line.substr(prefix.size(), end - prefix.size()));
+    }
+
+    for (const std::string& header : onDisk) {
+        // A header on disk but missing from the include list above.
+        CHECK(included.count(header) == 1u);
+        if (included.count(header) != 1u) {
+            std::printf("  unguarded header: core/include/vf/%s\n", header.c_str());
+        }
+    }
+    for (const std::string& header : included) {
+        // An include line left behind after a header was deleted or renamed.
+        CHECK(onDisk.count(header) == 1u);
+    }
+    CHECK_EQ(included.size(), onDisk.size());
+}
+
+// The two names that actually collided, now proven to coexist: an enum in
+// Survival.h and a struct in Damage.h, both reachable from one scope.
+VF_TEST(survivalAndDamageHeadersDeclareDistinctSourceTypes) {
+    DamageSource legacy = DamageSource::Fall;
+    CHECK(legacy == DamageSource::Fall);
+    CHECK(legacy != DamageSource::Lava);
+
+    HurtSource blow;
+    blow.type = DamageType::Fall;
+    blow.byPlayer = true;
+    blow.attackerId = 7;
+    CHECK(blow.type == DamageType::Fall);
+    CHECK(blow.byPlayer);
+    CHECK_EQ(blow.attackerId, 7);
+    CHECK_EQ(blow.ownerId, -1);
+
+    // Distinct types: the sizes below are unrelated, and the point is only
+    // that both names resolve in the same translation unit.
+    CHECK(sizeof(DamageSource) >= 1u);
+    CHECK(sizeof(HurtSource) > sizeof(DamageSource));
+}
+
+// Every block in the palette must map to a tile inside the atlas, on every
+// face. A block added without a faceTile case silently falls through to the
+// stone tile, which is the kind of thing nobody notices until the atlas is
+// resized. Both facts are checked here because faceTile and tileCount live in
+// the one header every module shares.
+VF_TEST(everyPaletteBlockMapsToATileInsideTheAtlas) {
+    const Face faces[6] = {Face::PosX, Face::NegX, Face::PosY,
+                           Face::NegY, Face::PosZ, Face::NegZ};
+    int highestTile = -1;
+    for (int i = 1; i < static_cast<int>(Block::Count); ++i) {
+        Block block = static_cast<Block>(i);
+        for (Face face : faces) {
+            int tile = faceTile(block, face);
+            CHECK(tile >= 0);
+            CHECK(tile < tileCount);
+            if (tile > highestTile) highestTile = tile;
+        }
+    }
+    // The atlas must not be padded with layers nothing references.
+    CHECK_EQ(highestTile, tileCount - 1);
+}
+
+// Opacity and solidity are independent flags, but light emission is only
+// meaningful within the 0..15 range the light engine packs into four bits.
+VF_TEST(blockLightEmissionStaysInsideTheFourBitLightRange) {
+    for (int i = 0; i < static_cast<int>(Block::Count); ++i) {
+        Block block = static_cast<Block>(i);
+        int emission = blockLightEmission(block);
+        CHECK(emission >= 0);
+        CHECK(emission <= 15);
+        if (isAir(block)) CHECK_EQ(emission, 0);
+    }
+    CHECK_EQ(blockLightEmission(Block::Glowstone), 15);
+    CHECK_EQ(blockLightEmission(Block::EndPortal), 15);
+    CHECK_EQ(blockLightEmission(Block::NetherPortal), 11);
+    CHECK_EQ(blockLightEmission(Block::Stone), 0);
+}
+
+// A transparent block must never be opaque, or the mesher would both skip the
+// neighbouring face and draw the block in the transparent pass.
+VF_TEST(transparentBlocksAreNeverAlsoOpaque) {
+    for (int i = 0; i < static_cast<int>(Block::Count); ++i) {
+        Block block = static_cast<Block>(i);
+        if (isTransparent(block)) CHECK(!isOpaque(block));
+        if (isOpaque(block)) CHECK(occludesLight(block));
+    }
+    CHECK(isTransparent(Block::Glass));
+    CHECK(!isOpaque(Block::Glass));
+    CHECK(isOpaque(Block::Stone));
+    CHECK(occludesLight(Block::Stone));
+}
+
+// faceVisible is the single rule the mesher trusts. It has to stay coherent
+// with isAir and isOpaque for the whole palette, not just for the handful of
+// blocks that existed when it was written.
+VF_TEST(faceVisibilityAgreesWithAirAndOpacityAcrossThePalette) {
+    for (int i = 0; i < static_cast<int>(Block::Count); ++i) {
+        Block self = static_cast<Block>(i);
+        CHECK(!faceVisible(self, Block::Stone));
+        if (isAir(self)) {
+            CHECK(!faceVisible(self, Block::Air));
+            continue;
+        }
+        CHECK(faceVisible(self, Block::Air));
+        CHECK(!faceVisible(self, self));
+    }
+}