perf(text): fold Ensure+Lookup into FontAtlas::EnsureAndGet (#53)

Per glyph, ShapeText did cache_.contains(key) (in Ensure) then
cache_.find(key) (in Lookup) — two independent hashes + node-chases of
the same key. Add EnsureAndGet returning const Glyph* with a single
find, insert-on-miss, returning &it->second. It returns nullptr only on
ShelfPlace failure, preserving the existing `if (g==nullptr) continue;`
behavior. Ensure now delegates to it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

implementations/Crafter.Graphics-FontAtlas.cpp

@@ -70,8 +70,12 @@ bool FontAtlas::ShelfPlace(int w, int h, int& outX, int& outY) {
 }
 
 bool FontAtlas::Ensure(Font& font, std::uint32_t codepoint) {
+    return EnsureAndGet(font, codepoint) != nullptr;
+}
+
+const Glyph* FontAtlas::EnsureAndGet(Font& font, std::uint32_t codepoint) {
     Key key{&font, codepoint};
-    if (cache_.contains(key)) return true;
+    if (auto it = cache_.find(key); it != cache_.end()) return &it->second;
 
     float fontScale = stbtt_ScaleForPixelHeight(&font.font, kBaseSize);
 
@@ -94,7 +98,7 @@ bool FontAtlas::Ensure(Font& font, std::uint32_t codepoint) {
         int px = 0, py = 0;
         if (!ShelfPlace(sw, sh, px, py)) {
             stbtt_FreeSDF(sdf, nullptr);
-            return false;
+            return nullptr;
         }
         std::uint8_t* dst = PixelPtr();
         for (int row = 0; row < sh; ++row) {
@@ -115,8 +119,7 @@ bool FontAtlas::Ensure(Font& font, std::uint32_t codepoint) {
         dirty = true;
     }
 
-    cache_.emplace(key, g);
-    return true;
+    return &cache_.emplace(key, g).first->second;
 }
 
 const Glyph* FontAtlas::Lookup(Font& font, std::uint32_t codepoint) const {

implementations/Crafter.Graphics-UI-Shared.cpp

@@ -75,8 +75,7 @@ std::uint32_t UIRenderer::ShapeText(Font& font, float pxSize,
             if (cp == 0) break;
             if (cp == '\n') { continue; }
 
-            fontAtlas->Ensure(font, cp);
-            const Glyph* g = fontAtlas->Lookup(font, cp);
+            const Glyph* g = fontAtlas->EnsureAndGet(font, cp);
             if (g == nullptr) continue;
 
             if (g->w > 0 && g->h > 0) {

interfaces/Crafter.Graphics-FontAtlas.cppm

@@ -66,6 +66,11 @@ export namespace Crafter {
         std::uint8_t* PixelPtr() noexcept;
 
         bool Ensure(Font& font, std::uint32_t codepoint);
+        // Ensure the glyph is in the atlas and return a pointer to it in one
+        // hash+probe. Returns nullptr only when a brand-new glyph cannot be
+        // placed (ShelfPlace failure); a glyph with no SDF coverage (e.g.
+        // space) still returns a valid pointer.
+        const Glyph* EnsureAndGet(Font& font, std::uint32_t codepoint);
         const Glyph* Lookup(Font& font, std::uint32_t codepoint) const;
         void Update(GraphicsCommandBuffer cmd);