feat(proto): GroupId, Orient, n-ary LayoutNode with external-tagged serde

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/spacesh-proto/src/ids.rs

@@ -16,3 +16,12 @@ impl std::fmt::Display for WorkspaceId {
         write!(f, "{}", self.0)
     }
 }
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub struct GroupId(pub String);
+
+impl std::fmt::Display for GroupId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}

crates/spacesh-proto/src/layout.rs

@@ -0,0 +1,58 @@
+use serde::{Deserialize, Serialize};
+use crate::ids::SurfaceId;
+
+/// Split orientation. `H` lays children left-to-right; `V` top-to-bottom.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum Orient {
+    H,
+    V,
+}
+
+/// Recursive n-ary layout tree. Externally tagged so JSON reads
+/// `{ "leaf": { "surface_id": "s_1" } }` / `{ "split": { ... } }`.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum LayoutNode {
+    Leaf { surface_id: SurfaceId },
+    Split {
+        orient: Orient,
+        ratios: Vec<f32>,
+        children: Vec<LayoutNode>,
+    },
+}
+
+impl LayoutNode {
+    pub fn leaf(id: SurfaceId) -> Self {
+        LayoutNode::Leaf { surface_id: id }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn leaf_serializes_externally_tagged() {
+        let n = LayoutNode::leaf(SurfaceId("s_1".into()));
+        let j = serde_json::to_string(&n).unwrap();
+        assert_eq!(j, r#"{"leaf":{"surface_id":"s_1"}}"#);
+    }
+
+    #[test]
+    fn split_round_trips() {
+        let n = LayoutNode::Split {
+            orient: Orient::V,
+            ratios: vec![0.5, 0.5],
+            children: vec![
+                LayoutNode::leaf(SurfaceId("s_1".into())),
+                LayoutNode::leaf(SurfaceId("s_2".into())),
+            ],
+        };
+        let j = serde_json::to_string(&n).unwrap();
+        assert!(j.contains(r#""split""#));
+        assert!(j.contains(r#""orient":"v""#));
+        let back: LayoutNode = serde_json::from_str(&j).unwrap();
+        assert_eq!(back, n);
+    }
+}

crates/spacesh-proto/src/lib.rs

@@ -1,6 +1,8 @@
 pub mod codec;
 pub mod ids;
+pub mod layout;
 pub mod message;
 
-pub use ids::{SurfaceId, WorkspaceId};
+pub use ids::{GroupId, SurfaceId, WorkspaceId};
+pub use layout::{LayoutNode, Orient};
 pub use message::{Cmd, Envelope, ErrorBody, Evt};