feat(core): add embedding hosts, persistent REPL state and bounded identities

examples/cli_registered_frontend.rs

@@ -0,0 +1,56 @@
+//! Public three-field CLI consumer: file registration does not select a REPL producer.
+#[cfg(feature = "cli")]
+mod consumer {
+    use std::sync::atomic::{AtomicUsize, Ordering};
+    use vm::{
+        CompileSourceFileOptions, FrontendIr, ParseError, SourceFrontendContext, SourcePlugin,
+    };
+
+    struct FileFrontend;
+    static FILE_FRONTEND: FileFrontend = FileFrontend;
+    static HOOKS: AtomicUsize = AtomicUsize::new(0);
+    impl SourcePlugin for FileFrontend {
+        fn descriptor(&self) -> vm::SourceFrontendDescriptor {
+            vm::SourceFrontendDescriptor {
+                id: vm::FrontendId::new("external-file-probe"),
+                extensions: &["external"],
+                typing_policy: vm::FrontendTypingPolicy::Strict,
+                supports_ownership_checking: true,
+            }
+        }
+        fn parse_source(
+            &self,
+            _: &str,
+            _: &SourceFrontendContext<'_>,
+        ) -> Result<FrontendIr, ParseError> {
+            HOOKS.fetch_add(1, Ordering::SeqCst);
+            Err(ParseError::new(
+                "this fixture only exercises native REPL selection",
+            ))
+        }
+        fn validate_typed_ir(&self, _: &vm::FrontendTypedIr<'_>) -> Result<(), vm::CompileError> {
+            HOOKS.fetch_add(1, Ordering::SeqCst);
+            panic!("unselected file hook must not run")
+        }
+    }
+
+    pub fn run() -> Result<(), Box<dyn std::error::Error>> {
+        vm::cli::main(vm::cli::CliRuntime {
+            binary_name: "cli-registered-frontend",
+            default_source: "unused.rss",
+            compile_options: || {
+                CompileSourceFileOptions::default().with_source_plugin(&FILE_FRONTEND)
+            },
+        })?;
+        assert_eq!(HOOKS.load(Ordering::SeqCst), 0);
+        println!("external-file-hooks=0");
+        Ok(())
+    }
+}
+
+#[cfg(feature = "cli")]
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    consumer::run()
+}
+#[cfg(not(feature = "cli"))]
+fn main() {}