feat(pen-core): skeleton crate (bucket A)

crates/pen-core/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "pen-core"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+description = "OpenPencil core engine (Action DSL / Signal graph) — bucket A in-WASM"
+
+[lib]
+name = "pen_core"
+path = "src/lib.rs"
+
+[dependencies]
+pen-types = { path = "../pen-types" }
+serde = { workspace = true }
+thiserror = { workspace = true }

crates/pen-core/src/lib.rs

@@ -0,0 +1,15 @@
+//! OpenPencil core engine.
+
+pub fn placeholder() -> String {
+    format!("pen-core ({})", pen_types::placeholder())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn skeleton_links_types() {
+        assert!(placeholder().contains("pen-types"));
+    }
+}