[sgl-router] Rename chat encoder to chat formatter (#39459)

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

experimental/sgl-router/tests/proxy/cache_aware_input_ids.rs

@@ -6,7 +6,7 @@
 //! skips re-tokenizing the same prompt). Asserts the gating contract through
 //! the real chat handler + a MockWorker backend:
 //!
-//! * A plain text chat request on the engine-equivalent chat-encoder path →
+//! * A plain text chat request on the engine-equivalent chat-formatter path →
 //!   the forwarded body carries `input_ids` AND retains `messages`.
 //! * A request carrying `tools` → `input_ids` omitted (the router's encoder
 //!   doesn't render tool schemas, so its ids would diverge from the engine).
@@ -35,8 +35,8 @@ fn build_ctx(url: String) -> Arc<AppContext> {
     let cfg = config();
     let tokenizers = Arc::new(TokenizerRegistry::load_from_config(&cfg).unwrap());
     assert!(
-        tokenizers.has_chat_encoder(MODEL),
-        "deepseek-v4 model id must auto-attach the built-in chat encoder"
+        tokenizers.has_chat_formatter(MODEL),
+        "deepseek-v4 model id must auto-attach the built-in chat formatter"
     );
     let registry = Arc::new(WorkerRegistry::default());
     let _ = registry.add(WorkerSpec {