Add host-configurable language service

doc/manual/souce/design/embedding-api.md

@@ -140,6 +140,48 @@ It only generates schema construction and typed decoding code.
 
 Both mechanisms share the same runtime evaluator, thunk model, and materialization rules.
 
+## Shared host environment
+
+An embedded application can implement `HostEnvironment` to keep loader creation and global binding setup in one place.
+Both production evaluation and semantic editor tooling create their engines from this environment, preventing the editor from drifting onto a separate validation path.
+
+```rust
+use decodal::{Engine, HostEnvironment};
+
+struct AppEnvironment;
+
+impl HostEnvironment for AppEnvironment {
+    type Loader = ContentLoader;
+
+    fn create_loader(&self) -> Self::Loader {
+        ContentLoader::new()
+    }
+
+    fn configure_engine(
+        &self,
+        engine: &mut Engine<Self::Loader>,
+    ) -> decodal::Result<()> {
+        engine.bind_global("Site", site_schema())?;
+        Ok(())
+    }
+}
+
+let environment = AppEnvironment;
+let mut engine = environment.create_engine()?;
+```
+
+The semantic service accepts the same environment by value:
+
+```rust
+use decodal_language_service::LanguageService;
+
+let service = LanguageService::new(&environment);
+let analysis = service.analyze("site.dcdl", "site.dcdl", source);
+```
+
+Each analysis uses a fresh engine and runs the normal parse, evaluate, and materialize pipeline.
+An environment may create loaders backed by shared filesystem, database, or editor-overlay state when repeated analysis needs a current workspace snapshot.
+
 ## Structured imports
 
 `ImportLoader::load` returns either `LoadedImport::Source` or `LoadedImport::Value`.

doc/manual/souce/design/execution-pipeline.md

@@ -23,6 +23,9 @@ materialize
 data / diagnostics
 ```
 
+Production applications and semantic language services can construct this pipeline through the same host-defined `HostEnvironment`.
+The environment creates the `ImportLoader` and installs host globals before the root module is registered.
+
 ## lexer / parser
 
 lexer / parser は source を AST に変換する。