Buffer Pre-Sizing & Memory Layout

1. A loaded template

Template
┌─────────────────────────────────────────────────────────────┐
│ name:   String   "feed/card.html"                           │
│ path:   PathBuf  "templates/feed/card.html"                 │
│ raw:    String   "<ui-card>{{title}}</ui-card>"             │
│ digest: [u8; 32] SHA-256 of raw                             │
│ chunks: Vec<Chunk>                                          │
│         ├── Chunk::Static(b"<ui-card>")                     │
│         ├── Chunk::Slot("title")                            │
│         └── Chunk::Static(b"</ui-card>")                    │
│ escape: bool                                                │
│ plan:   compiled static text + slot positions (private)     │
└─────────────────────────────────────────────────────────────┘

Each template keeps the raw text, the chunks and the compiled plan, so memory is roughly three times the template source size. Templates live as Arc<Template> in an RwLock<HashMap> inside an Arc<CacheStore>. They only change when the watch feature reloads them.

2. What a render allocates

During tpl.bind(&params) (anza::engine::slot::Plan::bind):

1. Prepare: Data<T> is serialized to a serde_json::Value once.
2. Resolve: each distinct placeholder name is looked up once (pair lists are scanned once for all names).
3. Allocate: one String, sized from the static text plus the values (or an estimate for maps and objects; it grows if values are longer).
4. Copy: static text and resolved values are written in order, escaped where escape applies.

Values that Params returns as Cow::Owned (numbers, Data, JSON values) allocate their own strings before being copied.