fix: mono pass seeds env.types and env.ctor_index for user ADTs

crates/ailang-check/src/mono.rs

@@ -403,6 +403,30 @@ pub fn build_workspace_env(ws: &Workspace) -> crate::Env {
             }
         }
     }
+
+    // Iter 22c: seed `env.types` and `env.ctor_index` from every
+    // module's `Def::Type` entries. `synth`'s bare-name `Term::Ctor`
+    // path (and three sibling sites in `lib.rs`) consult these flat
+    // tables; without them, re-running `synth` on an instance method
+    // body whose type references a user ADT yields `UnknownType`.
+    // Workspace-wide flat tables are safe here because `check_workspace`
+    // has already accepted the workspace, so duplicate names cannot
+    // occur. Mirrors `check_in_workspace` (lib.rs:1099-1128).
+    for m in ws.modules.values() {
+        for d in &m.defs {
+            if let Def::Type(td) = d {
+                for c in &td.ctors {
+                    env.ctor_index.insert(
+                        c.name.clone(),
+                        crate::CtorRef {
+                            type_name: td.name.clone(),
+                        },
+                    );
+                }
+                env.types.insert(td.name.clone(), td.clone());
+            }
+        }
+    }
     env
 }