[pitboss] phase 04: M4 — Rust harness (second-language validation)

src/dynamic/lang/mod.rs

@@ -4,6 +4,7 @@
 //! The top-level [`emit`] function dispatches on `spec.lang`.
 
 pub mod python;
+pub mod rust;
 
 use crate::dynamic::spec::HarnessSpec;
 use crate::evidence::UnsupportedReason;
@@ -14,16 +15,25 @@ use crate::symbol::Lang;
 pub struct HarnessSource {
     /// Harness source code as a UTF-8 string.
     pub source: String,
-    /// Filename for the harness (e.g. `"harness.py"`).
+    /// Filename for the harness (e.g. `"harness.py"`, `"src/main.rs"`).
     pub filename: String,
     /// Shell command to invoke the harness (relative to the workdir).
     pub command: Vec<String>,
+    /// Additional files to write to the workdir alongside the main source.
+    /// Each entry is `(relative_path, content)`. Subdirectories are created
+    /// automatically (e.g. `"Cargo.toml"` or `"src/entry.rs"`).
+    pub extra_files: Vec<(String, String)>,
+    /// Where to copy the entry source file (relative to workdir).
+    /// `None` = workdir root (Python default).
+    /// `Some("src/entry.rs")` = Rust module path.
+    pub entry_subpath: Option<String>,
 }
 
 /// Dispatch to the appropriate language emitter.
 pub fn emit(spec: &HarnessSpec) -> Result<HarnessSource, UnsupportedReason> {
     match spec.lang {
         Lang::Python => python::emit(spec),
+        Lang::Rust => rust::emit(spec),
         _ => Err(UnsupportedReason::LangUnsupported),
     }
 }