feat: add --graph ir-json flag to serialize raw IR from examples

Add IrJson variant to GraphType enum so paxos and map_reduce examples
can output serialized IR via --graph ir-json. Extract ir_to_json()
helper in compile::ir for shared use by BuiltFlow::ir_json() and
GraphApi::render().

Also adds a paxos_ir_json snapshot test in paxos_bench.

Author: Joe Hellerstein

hydro_lang/src/compile/built.rs

@@ -50,9 +50,9 @@ impl<'a> BuiltFlow<'a> {
     }
 
     /// Serialize the IR as JSON.
-    #[cfg(feature = "serde_json")]
+    #[cfg(feature = "viz")]
     pub fn ir_json(&self) -> Result<String, serde_json::Error> {
-        super::ir::serialize_dedup_shared(|| serde_json::to_string_pretty(&self.ir))
+        super::ir::ir_to_json(&self.ir)
     }
 
     /// Returns all raw location ID -> location name mappings.

hydro_lang/src/compile/ir/mod.rs

@@ -1716,6 +1716,12 @@ pub fn serialize_dedup_shared<T>(f: impl FnOnce() -> T) -> T {
     f()
 }
 
+/// Serialize a slice of [`HydroRoot`]s to a JSON string with shared-node deduplication.
+#[cfg(feature = "viz")]
+pub fn ir_to_json(ir: &[HydroRoot]) -> Result<String, serde_json::Error> {
+    serialize_dedup_shared(|| serde_json::to_string(ir))
+}
+
 /// RAII guard that saves/restores the `SERIALIZED_SHARED` thread-local,
 /// making `serialize_dedup_shared` re-entrant and panic-safe.
 struct SerializedSharedGuard {

hydro_lang/src/viz/api.rs

@@ -40,6 +40,10 @@ impl<'a> GraphApi<'a> {
             crate::viz::config::GraphType::Mermaid => render_hydro_ir_mermaid(self.ir, config),
             crate::viz::config::GraphType::Dot => render_hydro_ir_dot(self.ir, config),
             crate::viz::config::GraphType::Json => render_hydro_ir_json(self.ir, config),
+            crate::viz::config::GraphType::IrJson => {
+                crate::compile::ir::ir_to_json(self.ir)
+                    .expect("failed to serialize IR to JSON")
+            }
         }
     }
 

hydro_lang/src/viz/config.rs

@@ -9,6 +9,8 @@ pub enum GraphType {
     Dot,
     /// JSON format for Hydroscope interactive viewer.
     Json,
+    /// Raw serialized IR as JSON (full intermediate representation).
+    IrJson,
 }
 
 impl GraphType {
@@ -18,6 +20,7 @@ impl GraphType {
             GraphType::Mermaid => "mmd",
             GraphType::Dot => "dot",
             GraphType::Json => "json",
+            GraphType::IrJson => "ir.json",
         }
     }
 }

hydro_test/src/cluster/paxos_bench.rs

@@ -240,6 +240,40 @@ mod tests {
         });
     }
 
+    #[test]
+    fn paxos_ir_json() {
+        let mut builder = hydro_lang::compile::builder::FlowBuilder::new();
+        let proposers = builder.cluster();
+        let acceptors = builder.cluster();
+        let clients = builder.cluster();
+        let client_aggregator = builder.process();
+        let replicas = builder.cluster();
+
+        create_paxos(
+            &proposers,
+            &acceptors,
+            &clients,
+            &client_aggregator,
+            &replicas,
+        );
+        let built = builder.finalize();
+
+        let json = hydro_lang::compile::ir::serialize_dedup_shared(|| {
+            serde_json::to_string_pretty(built.ir()).unwrap()
+        });
+
+        // Redact absolute paths for CI portability.
+        let workspace_root = env!("CARGO_MANIFEST_DIR")
+            .strip_suffix("/hydro_test")
+            .or_else(|| env!("CARGO_MANIFEST_DIR").strip_suffix("\\hydro_test"))
+            .unwrap_or(env!("CARGO_MANIFEST_DIR"));
+        let json_escaped_root = workspace_root.replace('\\', "\\\\");
+        let json = json.replace(&json_escaped_root, "[workspace]");
+        let json = json.replace("\\\\", "/");
+
+        hydro_build_utils::assert_snapshot!(json);
+    }
+
     #[tokio::test]
     async fn paxos_some_throughput() {
         let mut builder = hydro_lang::compile::builder::FlowBuilder::new();