diff --git a/Cargo.lock b/Cargo.lock
index ab6f6e0649..3a643ffd39 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -351,9 +351,9 @@ checksum = "d71b6127be86fdcfddb610f7182ac57211d4b18a3e9c82eb2d17662f2227ad6a"
 
 [[package]]
 name = "capnp"
-version = "0.20.6"
+version = "0.21.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "053b81915c2ce1629b8fb964f578b18cb39b23ef9d5b24120d0dfc959569a1d9"
+checksum = "d55799fdec2a55eee8c267430d7464eb9c27ad2e5c8a49b433ff213b56852c7f"
 dependencies = [
  "embedded-io",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 5f956b65bd..2a19ff63c7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -42,7 +42,7 @@ debug_assert_with_mut_call = "warn"
 anyhow = "1.0.98"
 insta = { version = "1.43.1" }
 bitvec = "1.0.1"
-capnp = "0.20.6"
+capnp = "0.21.3"
 cgmath = "0.18.0"
 cool_asserts = "2.0.3"
 delegate = "0.13.4"
diff --git a/hugr-model/capnp/hugr-v0.capnp b/hugr-model/capnp/hugr-v0.capnp
index 18a13f71b1..7891b7f245 100644
--- a/hugr-model/capnp/hugr-v0.capnp
+++ b/hugr-model/capnp/hugr-v0.capnp
@@ -20,6 +20,12 @@ using LinkIndex = UInt32;
 
 struct Package {
     modules @0 :List(Module);
+    version @1 :Version;
+}
+
+struct Version {
+    major @0 :UInt32;
+    minor @1 :UInt32;
 }
 
 struct Module {
diff --git a/hugr-model/src/capnp/hugr_v0_capnp.rs b/hugr-model/src/capnp/hugr_v0_capnp.rs
index ec4e137acc..9e0a6ed7b3 100644
--- a/hugr-model/src/capnp/hugr_v0_capnp.rs
+++ b/hugr-model/src/capnp/hugr_v0_capnp.rs
@@ -72,11 +72,19 @@ pub mod package {
     pub fn has_modules(&self) -> bool {
       !self.reader.get_pointer_field(0).is_null()
     }
+    #[inline]
+    pub fn get_version(self) -> ::capnp::Result<crate::hugr_v0_capnp::version::Reader<'a>> {
+      ::capnp::traits::FromPointerReader::get_from_pointer(&self.reader.get_pointer_field(1), ::core::option::Option::None)
+    }
+    #[inline]
+    pub fn has_version(&self) -> bool {
+      !self.reader.get_pointer_field(1).is_null()
+    }
   }
 
   pub struct Builder<'a> { builder: ::capnp::private::layout::StructBuilder<'a> }
   impl <> ::capnp::traits::HasStructSize for Builder<'_,>  {
-    const STRUCT_SIZE: ::capnp::private::layout::StructSize = ::capnp::private::layout::StructSize { data: 0, pointers: 1 };
+    const STRUCT_SIZE: ::capnp::private::layout::StructSize = ::capnp::private::layout::StructSize { data: 0, pointers: 2 };
   }
   impl <> ::capnp::traits::HasTypeId for Builder<'_,>  {
     const TYPE_ID: u64 = _private::TYPE_ID;
@@ -142,6 +150,22 @@ pub mod package {
     pub fn has_modules(&self) -> bool {
       !self.builder.is_pointer_field_null(0)
     }
+    #[inline]
+    pub fn get_version(self) -> ::capnp::Result<crate::hugr_v0_capnp::version::Builder<'a>> {
+      ::capnp::traits::FromPointerBuilder::get_from_pointer(self.builder.get_pointer_field(1), ::core::option::Option::None)
+    }
+    #[inline]
+    pub fn set_version(&mut self, value: crate::hugr_v0_capnp::version::Reader<'_>) -> ::capnp::Result<()> {
+      ::capnp::traits::SetterInput::set_pointer_builder(self.builder.reborrow().get_pointer_field(1), value, false)
+    }
+    #[inline]
+    pub fn init_version(self, ) -> crate::hugr_v0_capnp::version::Builder<'a> {
+      ::capnp::traits::FromPointerBuilder::init_pointer(self.builder.get_pointer_field(1), 0)
+    }
+    #[inline]
+    pub fn has_version(&self) -> bool {
+      !self.builder.is_pointer_field_null(1)
+    }
   }
 
   pub struct Pipeline { _typeless: ::capnp::any_pointer::Pipeline }
@@ -151,19 +175,23 @@ pub mod package {
     }
   }
   impl Pipeline  {
+    pub fn get_version(&self) -> crate::hugr_v0_capnp::version::Pipeline {
+      ::capnp::capability::FromTypelessPipeline::new(self._typeless.get_pointer_field(1))
+    }
   }
   mod _private {
-    pub static ENCODED_NODE: [::capnp::Word; 37] = [
-      ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+    pub static ENCODED_NODE: [::capnp::Word; 53] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
       ::capnp::word(56, 36, 26, 168, 243, 12, 207, 208),
       ::capnp::word(20, 0, 0, 0, 1, 0, 0, 0),
       ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
-      ::capnp::word(1, 0, 7, 0, 0, 0, 0, 0),
+      ::capnp::word(2, 0, 7, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(93, 1, 0, 0, 166, 1, 0, 0),
       ::capnp::word(21, 0, 0, 0, 226, 0, 0, 0),
       ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
-      ::capnp::word(29, 0, 0, 0, 63, 0, 0, 0),
+      ::capnp::word(29, 0, 0, 0, 119, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
       ::capnp::word(99, 97, 112, 110, 112, 47, 104, 117),
@@ -171,14 +199,21 @@ pub mod package {
       ::capnp::word(112, 110, 112, 58, 80, 97, 99, 107),
       ::capnp::word(97, 103, 101, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 1, 0, 1, 0),
-      ::capnp::word(4, 0, 0, 0, 3, 0, 4, 0),
+      ::capnp::word(8, 0, 0, 0, 3, 0, 4, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 1, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
-      ::capnp::word(13, 0, 0, 0, 66, 0, 0, 0),
+      ::capnp::word(41, 0, 0, 0, 66, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
-      ::capnp::word(8, 0, 0, 0, 3, 0, 1, 0),
-      ::capnp::word(36, 0, 0, 0, 2, 0, 1, 0),
+      ::capnp::word(36, 0, 0, 0, 3, 0, 1, 0),
+      ::capnp::word(64, 0, 0, 0, 2, 0, 1, 0),
+      ::capnp::word(1, 0, 0, 0, 1, 0, 0, 0),
+      ::capnp::word(0, 0, 1, 0, 1, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(61, 0, 0, 0, 66, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(56, 0, 0, 0, 3, 0, 1, 0),
+      ::capnp::word(68, 0, 0, 0, 2, 0, 1, 0),
       ::capnp::word(109, 111, 100, 117, 108, 101, 115, 0),
       ::capnp::word(14, 0, 0, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -191,15 +226,24 @@ pub mod package {
       ::capnp::word(14, 0, 0, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(118, 101, 114, 115, 105, 111, 110, 0),
+      ::capnp::word(16, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(167, 171, 245, 145, 177, 155, 108, 182),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(16, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
     ];
     pub fn get_field_types(index: u16) -> ::capnp::introspect::Type {
       match index {
         0 => <::capnp::struct_list::Owned<crate::hugr_v0_capnp::module::Owned> as ::capnp::introspect::Introspect>::introspect(),
-        _ => panic!("invalid field index {}", index),
+        1 => <crate::hugr_v0_capnp::version::Owned as ::capnp::introspect::Introspect>::introspect(),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
       }
     }
     pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-      panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
     }
     pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
       encoded_node: &ENCODED_NODE,
@@ -207,13 +251,237 @@ pub mod package {
       members_by_discriminant: MEMBERS_BY_DISCRIMINANT,
       members_by_name: MEMBERS_BY_NAME,
     };
-    pub static NONUNION_MEMBERS : &[u16] = &[0];
+    pub static NONUNION_MEMBERS : &[u16] = &[0,1];
     pub static MEMBERS_BY_DISCRIMINANT : &[u16] = &[];
-    pub static MEMBERS_BY_NAME : &[u16] = &[0];
+    pub static MEMBERS_BY_NAME : &[u16] = &[0,1];
     pub const TYPE_ID: u64 = 0xd0cf_0cf3_a81a_2438;
   }
 }
 
+pub mod version {
+  #[derive(Copy, Clone)]
+  pub struct Owned(());
+  impl ::capnp::introspect::Introspect for Owned { fn introspect() -> ::capnp::introspect::Type { ::capnp::introspect::TypeVariant::Struct(::capnp::introspect::RawBrandedStructSchema { generic: &_private::RAW_SCHEMA, field_types: _private::get_field_types, annotation_types: _private::get_annotation_types }).into() } }
+  impl ::capnp::traits::Owned for Owned { type Reader<'a> = Reader<'a>; type Builder<'a> = Builder<'a>; }
+  impl ::capnp::traits::OwnedStruct for Owned { type Reader<'a> = Reader<'a>; type Builder<'a> = Builder<'a>; }
+  impl ::capnp::traits::Pipelined for Owned { type Pipeline = Pipeline; }
+
+  pub struct Reader<'a> { reader: ::capnp::private::layout::StructReader<'a> }
+  impl <> ::core::marker::Copy for Reader<'_,>  {}
+  impl <> ::core::clone::Clone for Reader<'_,>  {
+    fn clone(&self) -> Self { *self }
+  }
+
+  impl <> ::capnp::traits::HasTypeId for Reader<'_,>  {
+    const TYPE_ID: u64 = _private::TYPE_ID;
+  }
+  impl <'a,> ::core::convert::From<::capnp::private::layout::StructReader<'a>> for Reader<'a,>  {
+    fn from(reader: ::capnp::private::layout::StructReader<'a>) -> Self {
+      Self { reader,  }
+    }
+  }
+
+  impl <'a,> ::core::convert::From<Reader<'a,>> for ::capnp::dynamic_value::Reader<'a>  {
+    fn from(reader: Reader<'a,>) -> Self {
+      Self::Struct(::capnp::dynamic_struct::Reader::new(reader.reader, ::capnp::schema::StructSchema::new(::capnp::introspect::RawBrandedStructSchema { generic: &_private::RAW_SCHEMA, field_types: _private::get_field_types::<>, annotation_types: _private::get_annotation_types::<>})))
+    }
+  }
+
+  impl <> ::core::fmt::Debug for Reader<'_,>  {
+    fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>) -> ::core::result::Result<(), ::core::fmt::Error> {
+      core::fmt::Debug::fmt(&::core::convert::Into::<::capnp::dynamic_value::Reader<'_>>::into(*self), f)
+    }
+  }
+
+  impl <'a,> ::capnp::traits::FromPointerReader<'a> for Reader<'a,>  {
+    fn get_from_pointer(reader: &::capnp::private::layout::PointerReader<'a>, default: ::core::option::Option<&'a [::capnp::Word]>) -> ::capnp::Result<Self> {
+      ::core::result::Result::Ok(reader.get_struct(default)?.into())
+    }
+  }
+
+  impl <'a,> ::capnp::traits::IntoInternalStructReader<'a> for Reader<'a,>  {
+    fn into_internal_struct_reader(self) -> ::capnp::private::layout::StructReader<'a> {
+      self.reader
+    }
+  }
+
+  impl <'a,> ::capnp::traits::Imbue<'a> for Reader<'a,>  {
+    fn imbue(&mut self, cap_table: &'a ::capnp::private::layout::CapTable) {
+      self.reader.imbue(::capnp::private::layout::CapTableReader::Plain(cap_table))
+    }
+  }
+
+  impl <> Reader<'_,>  {
+    pub fn reborrow(&self) -> Reader<'_,> {
+      Self { .. *self }
+    }
+
+    pub fn total_size(&self) -> ::capnp::Result<::capnp::MessageSize> {
+      self.reader.total_size()
+    }
+    #[inline]
+    pub fn get_major(self) -> u32 {
+      self.reader.get_data_field::<u32>(0)
+    }
+    #[inline]
+    pub fn get_minor(self) -> u32 {
+      self.reader.get_data_field::<u32>(1)
+    }
+  }
+
+  pub struct Builder<'a> { builder: ::capnp::private::layout::StructBuilder<'a> }
+  impl <> ::capnp::traits::HasStructSize for Builder<'_,>  {
+    const STRUCT_SIZE: ::capnp::private::layout::StructSize = ::capnp::private::layout::StructSize { data: 1, pointers: 0 };
+  }
+  impl <> ::capnp::traits::HasTypeId for Builder<'_,>  {
+    const TYPE_ID: u64 = _private::TYPE_ID;
+  }
+  impl <'a,> ::core::convert::From<::capnp::private::layout::StructBuilder<'a>> for Builder<'a,>  {
+    fn from(builder: ::capnp::private::layout::StructBuilder<'a>) -> Self {
+      Self { builder,  }
+    }
+  }
+
+  impl <'a,> ::core::convert::From<Builder<'a,>> for ::capnp::dynamic_value::Builder<'a>  {
+    fn from(builder: Builder<'a,>) -> Self {
+      Self::Struct(::capnp::dynamic_struct::Builder::new(builder.builder, ::capnp::schema::StructSchema::new(::capnp::introspect::RawBrandedStructSchema { generic: &_private::RAW_SCHEMA, field_types: _private::get_field_types::<>, annotation_types: _private::get_annotation_types::<>})))
+    }
+  }
+
+  impl <'a,> ::capnp::traits::ImbueMut<'a> for Builder<'a,>  {
+    fn imbue_mut(&mut self, cap_table: &'a mut ::capnp::private::layout::CapTable) {
+      self.builder.imbue(::capnp::private::layout::CapTableBuilder::Plain(cap_table))
+    }
+  }
+
+  impl <'a,> ::capnp::traits::FromPointerBuilder<'a> for Builder<'a,>  {
+    fn init_pointer(builder: ::capnp::private::layout::PointerBuilder<'a>, _size: u32) -> Self {
+      builder.init_struct(<Self as ::capnp::traits::HasStructSize>::STRUCT_SIZE).into()
+    }
+    fn get_from_pointer(builder: ::capnp::private::layout::PointerBuilder<'a>, default: ::core::option::Option<&'a [::capnp::Word]>) -> ::capnp::Result<Self> {
+      ::core::result::Result::Ok(builder.get_struct(<Self as ::capnp::traits::HasStructSize>::STRUCT_SIZE, default)?.into())
+    }
+  }
+
+  impl <> ::capnp::traits::SetterInput<Owned<>> for Reader<'_,>  {
+    fn set_pointer_builder(mut pointer: ::capnp::private::layout::PointerBuilder<'_>, value: Self, canonicalize: bool) -> ::capnp::Result<()> { pointer.set_struct(&value.reader, canonicalize) }
+  }
+
+  impl <'a,> Builder<'a,>  {
+    pub fn into_reader(self) -> Reader<'a,> {
+      self.builder.into_reader().into()
+    }
+    pub fn reborrow(&mut self) -> Builder<'_,> {
+      Builder { builder: self.builder.reborrow() }
+    }
+    pub fn reborrow_as_reader(&self) -> Reader<'_,> {
+      self.builder.as_reader().into()
+    }
+
+    pub fn total_size(&self) -> ::capnp::Result<::capnp::MessageSize> {
+      self.builder.as_reader().total_size()
+    }
+    #[inline]
+    pub fn get_major(self) -> u32 {
+      self.builder.get_data_field::<u32>(0)
+    }
+    #[inline]
+    pub fn set_major(&mut self, value: u32)  {
+      self.builder.set_data_field::<u32>(0, value);
+    }
+    #[inline]
+    pub fn get_minor(self) -> u32 {
+      self.builder.get_data_field::<u32>(1)
+    }
+    #[inline]
+    pub fn set_minor(&mut self, value: u32)  {
+      self.builder.set_data_field::<u32>(1, value);
+    }
+  }
+
+  pub struct Pipeline { _typeless: ::capnp::any_pointer::Pipeline }
+  impl ::capnp::capability::FromTypelessPipeline for Pipeline {
+    fn new(typeless: ::capnp::any_pointer::Pipeline) -> Self {
+      Self { _typeless: typeless,  }
+    }
+  }
+  impl Pipeline  {
+  }
+  mod _private {
+    pub static ENCODED_NODE: [::capnp::Word; 49] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
+      ::capnp::word(167, 171, 245, 145, 177, 155, 108, 182),
+      ::capnp::word(20, 0, 0, 0, 1, 0, 1, 0),
+      ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
+      ::capnp::word(0, 0, 7, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(168, 1, 0, 0, 230, 1, 0, 0),
+      ::capnp::word(21, 0, 0, 0, 226, 0, 0, 0),
+      ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(29, 0, 0, 0, 119, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(99, 97, 112, 110, 112, 47, 104, 117),
+      ::capnp::word(103, 114, 45, 118, 48, 46, 99, 97),
+      ::capnp::word(112, 110, 112, 58, 86, 101, 114, 115),
+      ::capnp::word(105, 111, 110, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 1, 0, 1, 0),
+      ::capnp::word(8, 0, 0, 0, 3, 0, 4, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 1, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(41, 0, 0, 0, 50, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(36, 0, 0, 0, 3, 0, 1, 0),
+      ::capnp::word(48, 0, 0, 0, 2, 0, 1, 0),
+      ::capnp::word(1, 0, 0, 0, 1, 0, 0, 0),
+      ::capnp::word(0, 0, 1, 0, 1, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(45, 0, 0, 0, 50, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(40, 0, 0, 0, 3, 0, 1, 0),
+      ::capnp::word(52, 0, 0, 0, 2, 0, 1, 0),
+      ::capnp::word(109, 97, 106, 111, 114, 0, 0, 0),
+      ::capnp::word(8, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(8, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(109, 105, 110, 111, 114, 0, 0, 0),
+      ::capnp::word(8, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(8, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+    ];
+    pub fn get_field_types(index: u16) -> ::capnp::introspect::Type {
+      match index {
+        0 => <u32 as ::capnp::introspect::Introspect>::introspect(),
+        1 => <u32 as ::capnp::introspect::Introspect>::introspect(),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
+      }
+    }
+    pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
+    }
+    pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
+      encoded_node: &ENCODED_NODE,
+      nonunion_members: NONUNION_MEMBERS,
+      members_by_discriminant: MEMBERS_BY_DISCRIMINANT,
+      members_by_name: MEMBERS_BY_NAME,
+    };
+    pub static NONUNION_MEMBERS : &[u16] = &[0,1];
+    pub static MEMBERS_BY_DISCRIMINANT : &[u16] = &[];
+    pub static MEMBERS_BY_NAME : &[u16] = &[0,1];
+    pub const TYPE_ID: u64 = 0xb66c_9bb1_91f5_aba7;
+  }
+}
+
 pub mod module {
   #[derive(Copy, Clone)]
   pub struct Owned(());
@@ -424,13 +692,14 @@ pub mod module {
   impl Pipeline  {
   }
   mod _private {
-    pub static ENCODED_NODE: [::capnp::Word; 90] = [
-      ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+    pub static ENCODED_NODE: [::capnp::Word; 91] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
       ::capnp::word(167, 107, 35, 13, 152, 216, 48, 189),
       ::capnp::word(20, 0, 0, 0, 1, 0, 1, 0),
       ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
       ::capnp::word(3, 0, 7, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(232, 1, 0, 0, 98, 2, 0, 0),
       ::capnp::word(21, 0, 0, 0, 218, 0, 0, 0),
       ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -522,11 +791,11 @@ pub mod module {
         1 => <::capnp::struct_list::Owned<crate::hugr_v0_capnp::node::Owned> as ::capnp::introspect::Introspect>::introspect(),
         2 => <::capnp::struct_list::Owned<crate::hugr_v0_capnp::region::Owned> as ::capnp::introspect::Introspect>::introspect(),
         3 => <::capnp::struct_list::Owned<crate::hugr_v0_capnp::term::Owned> as ::capnp::introspect::Introspect>::introspect(),
-        _ => panic!("invalid field index {}", index),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
       }
     }
     pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-      panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
     }
     pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
       encoded_node: &ENCODED_NODE,
@@ -802,13 +1071,14 @@ pub mod node {
     }
   }
   mod _private {
-    pub static ENCODED_NODE: [::capnp::Word; 126] = [
-      ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+    pub static ENCODED_NODE: [::capnp::Word; 127] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
       ::capnp::word(108, 130, 159, 249, 96, 124, 57, 228),
       ::capnp::word(20, 0, 0, 0, 1, 0, 1, 0),
       ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
       ::capnp::word(5, 0, 7, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(100, 2, 0, 0, 46, 3, 0, 0),
       ::capnp::word(21, 0, 0, 0, 202, 0, 0, 0),
       ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -938,11 +1208,11 @@ pub mod node {
         3 => <::capnp::primitive_list::Owned<u32> as ::capnp::introspect::Introspect>::introspect(),
         4 => <::capnp::primitive_list::Owned<u32> as ::capnp::introspect::Introspect>::introspect(),
         5 => <u32 as ::capnp::introspect::Introspect>::introspect(),
-        _ => panic!("invalid field index {}", index),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
       }
     }
     pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-      panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
     }
     pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
       encoded_node: &ENCODED_NODE,
@@ -1393,13 +1663,14 @@ pub mod operation {
   impl Pipeline  {
   }
   mod _private {
-    pub static ENCODED_NODE: [::capnp::Word; 229] = [
-      ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+    pub static ENCODED_NODE: [::capnp::Word; 230] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
       ::capnp::word(216, 191, 119, 93, 53, 241, 240, 155),
       ::capnp::word(20, 0, 0, 0, 1, 0, 1, 0),
       ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
       ::capnp::word(1, 0, 7, 0, 0, 0, 14, 0),
       ::capnp::word(2, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(48, 3, 0, 0, 38, 5, 0, 0),
       ::capnp::word(21, 0, 0, 0, 242, 0, 0, 0),
       ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -1640,11 +1911,11 @@ pub mod operation {
         11 => <::capnp::text::Owned as ::capnp::introspect::Introspect>::introspect(),
         12 => <crate::hugr_v0_capnp::symbol::Owned as ::capnp::introspect::Introspect>::introspect(),
         13 => <crate::hugr_v0_capnp::symbol::Owned as ::capnp::introspect::Introspect>::introspect(),
-        _ => panic!("invalid field index {}", index),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
       }
     }
     pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-      panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
     }
     pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
       encoded_node: &ENCODED_NODE,
@@ -1841,13 +2112,14 @@ pub mod operation {
       }
     }
     mod _private {
-      pub static ENCODED_NODE: [::capnp::Word; 48] = [
-        ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+      pub static ENCODED_NODE: [::capnp::Word; 49] = [
+        ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
         ::capnp::word(156, 202, 42, 93, 60, 14, 161, 193),
         ::capnp::word(30, 0, 0, 0, 1, 0, 1, 0),
         ::capnp::word(216, 191, 119, 93, 53, 241, 240, 155),
         ::capnp::word(1, 0, 7, 0, 1, 0, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+        ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
         ::capnp::word(21, 0, 0, 0, 66, 1, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -1895,11 +2167,11 @@ pub mod operation {
         match index {
           0 => <crate::hugr_v0_capnp::symbol::Owned as ::capnp::introspect::Introspect>::introspect(),
           1 => <u32 as ::capnp::introspect::Introspect>::introspect(),
-          _ => panic!("invalid field index {}", index),
+          _ => ::capnp::introspect::panic_invalid_field_index(index),
         }
       }
       pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-        panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+        ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
       }
       pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
         encoded_node: &ENCODED_NODE,
@@ -2137,13 +2409,14 @@ pub mod symbol {
   impl Pipeline  {
   }
   mod _private {
-    pub static ENCODED_NODE: [::capnp::Word; 104] = [
-      ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+    pub static ENCODED_NODE: [::capnp::Word; 105] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
       ::capnp::word(63, 209, 84, 70, 225, 154, 206, 223),
       ::capnp::word(20, 0, 0, 0, 1, 0, 1, 0),
       ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
       ::capnp::word(3, 0, 7, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(40, 5, 0, 0, 195, 5, 0, 0),
       ::capnp::word(21, 0, 0, 0, 218, 0, 0, 0),
       ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -2250,11 +2523,11 @@ pub mod symbol {
         2 => <::capnp::primitive_list::Owned<u32> as ::capnp::introspect::Introspect>::introspect(),
         3 => <u32 as ::capnp::introspect::Introspect>::introspect(),
         4 => <crate::hugr_v0_capnp::Visibility as ::capnp::introspect::Introspect>::introspect(),
-        _ => panic!("invalid field index {}", index),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
       }
     }
     pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-      panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
     }
     pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
       encoded_node: &ENCODED_NODE,
@@ -2542,13 +2815,14 @@ pub mod region {
     }
   }
   mod _private {
-    pub static ENCODED_NODE: [::capnp::Word; 141] = [
-      ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+    pub static ENCODED_NODE: [::capnp::Word; 142] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
       ::capnp::word(225, 113, 253, 231, 231, 39, 130, 153),
       ::capnp::word(20, 0, 0, 0, 1, 0, 1, 0),
       ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
       ::capnp::word(5, 0, 7, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(197, 5, 0, 0, 168, 6, 0, 0),
       ::capnp::word(21, 0, 0, 0, 218, 0, 0, 0),
       ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -2694,11 +2968,11 @@ pub mod region {
         4 => <::capnp::primitive_list::Owned<u32> as ::capnp::introspect::Introspect>::introspect(),
         5 => <u32 as ::capnp::introspect::Introspect>::introspect(),
         6 => <crate::hugr_v0_capnp::region_scope::Owned as ::capnp::introspect::Introspect>::introspect(),
-        _ => panic!("invalid field index {}", index),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
       }
     }
     pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-      panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
     }
     pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
       encoded_node: &ENCODED_NODE,
@@ -2863,13 +3137,14 @@ pub mod region_scope {
   impl Pipeline  {
   }
   mod _private {
-    pub static ENCODED_NODE: [::capnp::Word; 48] = [
-      ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+    pub static ENCODED_NODE: [::capnp::Word; 49] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
       ::capnp::word(163, 135, 81, 30, 243, 205, 148, 170),
       ::capnp::word(20, 0, 0, 0, 1, 0, 1, 0),
       ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
       ::capnp::word(0, 0, 7, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(170, 6, 0, 0, 236, 6, 0, 0),
       ::capnp::word(21, 0, 0, 0, 2, 1, 0, 0),
       ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -2917,11 +3192,11 @@ pub mod region_scope {
       match index {
         0 => <u32 as ::capnp::introspect::Introspect>::introspect(),
         1 => <u32 as ::capnp::introspect::Introspect>::introspect(),
-        _ => panic!("invalid field index {}", index),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
       }
     }
     pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-      panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
     }
     pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
       encoded_node: &ENCODED_NODE,
@@ -2969,13 +3244,14 @@ impl ::capnp::traits::HasTypeId for RegionKind {
   const TYPE_ID: u64 = 0xe457_1af6_23a3_76b4u64;
 }
 mod region_kind {
-pub static ENCODED_NODE: [::capnp::Word; 32] = [
-  ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+pub static ENCODED_NODE: [::capnp::Word; 33] = [
+  ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
   ::capnp::word(180, 118, 163, 35, 246, 26, 87, 228),
   ::capnp::word(20, 0, 0, 0, 2, 0, 0, 0),
   ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
   ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
   ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+  ::capnp::word(238, 6, 0, 0, 53, 7, 0, 0),
   ::capnp::word(21, 0, 0, 0, 250, 0, 0, 0),
   ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
   ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -3004,7 +3280,7 @@ pub static ENCODED_NODE: [::capnp::Word; 32] = [
   ::capnp::word(109, 111, 100, 117, 108, 101, 0, 0),
 ];
 pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-  panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+  ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
 }
 }
 
@@ -3361,13 +3637,14 @@ pub mod term {
   impl Pipeline  {
   }
   mod _private {
-    pub static ENCODED_NODE: [::capnp::Word; 167] = [
-      ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+    pub static ENCODED_NODE: [::capnp::Word; 168] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
       ::capnp::word(178, 107, 91, 137, 60, 121, 191, 207),
       ::capnp::word(20, 0, 0, 0, 1, 0, 2, 0),
       ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
       ::capnp::word(1, 0, 7, 0, 0, 0, 10, 0),
       ::capnp::word(2, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(55, 7, 0, 0, 105, 9, 0, 0),
       ::capnp::word(21, 0, 0, 0, 202, 0, 0, 0),
       ::capnp::word(33, 0, 0, 0, 23, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -3542,11 +3819,11 @@ pub mod term {
         7 => <u32 as ::capnp::introspect::Introspect>::introspect(),
         8 => <() as ::capnp::introspect::Introspect>::introspect(),
         9 => <::capnp::struct_list::Owned<crate::hugr_v0_capnp::term::seq_part::Owned> as ::capnp::introspect::Introspect>::introspect(),
-        _ => panic!("invalid field index {}", index),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
       }
     }
     pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-      panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
     }
     pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
       encoded_node: &ENCODED_NODE,
@@ -3744,13 +4021,14 @@ pub mod term {
     impl Pipeline  {
     }
     mod _private {
-      pub static ENCODED_NODE: [::capnp::Word; 49] = [
-        ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+      pub static ENCODED_NODE: [::capnp::Word; 50] = [
+        ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
         ::capnp::word(136, 151, 188, 135, 237, 57, 73, 141),
         ::capnp::word(25, 0, 0, 0, 1, 0, 1, 0),
         ::capnp::word(178, 107, 91, 137, 60, 121, 191, 207),
         ::capnp::word(0, 0, 7, 0, 0, 0, 2, 0),
         ::capnp::word(2, 0, 0, 0, 0, 0, 0, 0),
+        ::capnp::word(251, 8, 0, 0, 103, 9, 0, 0),
         ::capnp::word(21, 0, 0, 0, 10, 1, 0, 0),
         ::capnp::word(37, 0, 0, 0, 7, 0, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -3799,11 +4077,11 @@ pub mod term {
         match index {
           0 => <u32 as ::capnp::introspect::Introspect>::introspect(),
           1 => <u32 as ::capnp::introspect::Introspect>::introspect(),
-          _ => panic!("invalid field index {}", index),
+          _ => ::capnp::introspect::panic_invalid_field_index(index),
         }
       }
       pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-        panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+        ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
       }
       pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
         encoded_node: &ENCODED_NODE,
@@ -3986,13 +4264,14 @@ pub mod term {
     impl Pipeline  {
     }
     mod _private {
-      pub static ENCODED_NODE: [::capnp::Word; 51] = [
-        ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+      pub static ENCODED_NODE: [::capnp::Word; 52] = [
+        ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
         ::capnp::word(150, 98, 109, 181, 159, 123, 122, 222),
         ::capnp::word(25, 0, 0, 0, 1, 0, 2, 0),
         ::capnp::word(178, 107, 91, 137, 60, 121, 191, 207),
         ::capnp::word(1, 0, 7, 0, 1, 0, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+        ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
         ::capnp::word(21, 0, 0, 0, 250, 0, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -4043,11 +4322,11 @@ pub mod term {
         match index {
           0 => <u32 as ::capnp::introspect::Introspect>::introspect(),
           1 => <::capnp::primitive_list::Owned<u32> as ::capnp::introspect::Introspect>::introspect(),
-          _ => panic!("invalid field index {}", index),
+          _ => ::capnp::introspect::panic_invalid_field_index(index),
         }
       }
       pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-        panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+        ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
       }
       pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
         encoded_node: &ENCODED_NODE,
@@ -4212,13 +4491,14 @@ pub mod term {
     impl Pipeline  {
     }
     mod _private {
-      pub static ENCODED_NODE: [::capnp::Word; 48] = [
-        ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+      pub static ENCODED_NODE: [::capnp::Word; 49] = [
+        ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
         ::capnp::word(55, 205, 218, 56, 109, 17, 119, 134),
         ::capnp::word(25, 0, 0, 0, 1, 0, 2, 0),
         ::capnp::word(178, 107, 91, 137, 60, 121, 191, 207),
         ::capnp::word(1, 0, 7, 0, 1, 0, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+        ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
         ::capnp::word(21, 0, 0, 0, 18, 1, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
         ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -4266,11 +4546,11 @@ pub mod term {
         match index {
           0 => <u32 as ::capnp::introspect::Introspect>::introspect(),
           1 => <u16 as ::capnp::introspect::Introspect>::introspect(),
-          _ => panic!("invalid field index {}", index),
+          _ => ::capnp::introspect::panic_invalid_field_index(index),
         }
       }
       pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-        panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+        ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
       }
       pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
         encoded_node: &ENCODED_NODE,
@@ -4448,13 +4728,14 @@ pub mod param {
   impl Pipeline  {
   }
   mod _private {
-    pub static ENCODED_NODE: [::capnp::Word; 48] = [
-      ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+    pub static ENCODED_NODE: [::capnp::Word; 49] = [
+      ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
       ::capnp::word(232, 73, 199, 85, 129, 167, 53, 211),
       ::capnp::word(20, 0, 0, 0, 1, 0, 1, 0),
       ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
       ::capnp::word(1, 0, 7, 0, 0, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+      ::capnp::word(107, 9, 0, 0, 163, 9, 0, 0),
       ::capnp::word(21, 0, 0, 0, 210, 0, 0, 0),
       ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
       ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -4502,11 +4783,11 @@ pub mod param {
       match index {
         0 => <::capnp::text::Owned as ::capnp::introspect::Introspect>::introspect(),
         1 => <u32 as ::capnp::introspect::Introspect>::introspect(),
-        _ => panic!("invalid field index {}", index),
+        _ => ::capnp::introspect::panic_invalid_field_index(index),
       }
     }
     pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-      panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+      ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
     }
     pub static RAW_SCHEMA: ::capnp::introspect::RawStructSchema = ::capnp::introspect::RawStructSchema {
       encoded_node: &ENCODED_NODE,
@@ -4554,13 +4835,14 @@ impl ::capnp::traits::HasTypeId for Visibility {
   const TYPE_ID: u64 = 0x8d83_15f2_7a68_8301u64;
 }
 mod visibility {
-pub static ENCODED_NODE: [::capnp::Word; 31] = [
-  ::capnp::word(0, 0, 0, 0, 5, 0, 6, 0),
+pub static ENCODED_NODE: [::capnp::Word; 32] = [
+  ::capnp::word(0, 0, 0, 0, 6, 0, 6, 0),
   ::capnp::word(1, 131, 104, 122, 242, 21, 131, 141),
   ::capnp::word(20, 0, 0, 0, 2, 0, 0, 0),
   ::capnp::word(1, 150, 80, 40, 197, 50, 43, 224),
   ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
   ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
+  ::capnp::word(165, 9, 0, 0, 235, 9, 0, 0),
   ::capnp::word(21, 0, 0, 0, 250, 0, 0, 0),
   ::capnp::word(33, 0, 0, 0, 7, 0, 0, 0),
   ::capnp::word(0, 0, 0, 0, 0, 0, 0, 0),
@@ -4588,6 +4870,6 @@ pub static ENCODED_NODE: [::capnp::Word; 31] = [
   ::capnp::word(112, 117, 98, 108, 105, 99, 0, 0),
 ];
 pub fn get_annotation_types(child_index: Option<u16>, index: u32) -> ::capnp::introspect::Type {
-  panic!("invalid annotation indices ({:?}, {}) ", child_index, index)
+  ::capnp::introspect::panic_invalid_annotation_indices(child_index, index)
 }
 }
diff --git a/hugr-model/src/lib.rs b/hugr-model/src/lib.rs
index c139cefc42..f99ecfe0d3 100644
--- a/hugr-model/src/lib.rs
+++ b/hugr-model/src/lib.rs
@@ -5,6 +5,8 @@
 mod capnp;
 
 pub mod v0;
+mod version;
+pub use version::*;
 
 // This is required here since the generated code assumes it's in the package root.
 use capnp::hugr_v0_capnp;
diff --git a/hugr-model/src/v0/binary/read.rs b/hugr-model/src/v0/binary/read.rs
index 05ada8dcfe..a2b6ef38e9 100644
--- a/hugr-model/src/v0/binary/read.rs
+++ b/hugr-model/src/v0/binary/read.rs
@@ -1,6 +1,6 @@
 use crate::capnp::hugr_v0_capnp as hugr_capnp;
-use crate::v0 as model;
 use crate::v0::table;
+use crate::{Version, v0 as model};
 use bumpalo::Bump;
 use bumpalo::collections::Vec as BumpVec;
 use std::io::BufRead;
@@ -13,6 +13,15 @@ pub enum ReadError {
     #[from(forward)]
     /// An error encountered while decoding a model from a `capnproto` buffer.
     DecodingError(capnp::Error),
+
+    /// The file could not be read due to a version mismatch.
+    #[display("Can not read file with version {actual} (tooling version {current}).")]
+    VersionError {
+        /// The current version of the hugr-model format.
+        current: Version,
+        /// The version of the hugr-model format in the file.
+        actual: Version,
+    },
 }
 
 type ReadResult<T> = Result<T, ReadError>;
@@ -58,6 +67,16 @@ fn read_package<'a>(
     bump: &'a Bump,
     reader: hugr_capnp::package::Reader,
 ) -> ReadResult<table::Package<'a>> {
+    let version = read_version(reader.get_version()?)?;
+    let current_version = Version::current();
+
+    if version.major != current_version.major || version.minor > current_version.minor {
+        return Err(ReadError::VersionError {
+            current: current_version,
+            actual: version,
+        });
+    }
+
     let modules = reader
         .get_modules()?
         .iter()
@@ -67,6 +86,12 @@ fn read_package<'a>(
     Ok(table::Package { modules })
 }
 
+fn read_version(reader: hugr_capnp::version::Reader) -> ReadResult<Version> {
+    let major = reader.get_major();
+    let minor = reader.get_minor();
+    Ok(Version { minor, major })
+}
+
 fn read_module<'a>(
     bump: &'a Bump,
     reader: hugr_capnp::module::Reader,
diff --git a/hugr-model/src/v0/binary/write.rs b/hugr-model/src/v0/binary/write.rs
index 0ac28b15ef..1fcf3d0c15 100644
--- a/hugr-model/src/v0/binary/write.rs
+++ b/hugr-model/src/v0/binary/write.rs
@@ -1,8 +1,8 @@
 use std::io::Write;
 
+use crate::Version;
 use crate::capnp::hugr_v0_capnp as hugr_capnp;
-use crate::v0 as model;
-use crate::v0::table;
+use crate::v0::{self as model, table};
 
 /// An error encounter while serializing a model.
 #[derive(Debug, derive_more::From, derive_more::Display, derive_more::Error)]
@@ -47,6 +47,12 @@ pub fn write_to_vec(package: &table::Package) -> Vec<u8> {
 
 fn write_package(mut builder: hugr_capnp::package::Builder, package: &table::Package) {
     write_list!(builder, init_modules, write_module, package.modules);
+    write_version(builder.init_version(), Version::current());
+}
+
+fn write_version(mut builder: hugr_capnp::version::Builder, version: Version) {
+    builder.set_major(version.major);
+    builder.set_minor(version.minor);
 }
 
 fn write_module(mut builder: hugr_capnp::module::Builder, module: &table::Module) {
diff --git a/hugr-model/src/version.rs b/hugr-model/src/version.rs
new file mode 100644
index 0000000000..2cbb2f8d3e
--- /dev/null
+++ b/hugr-model/src/version.rs
@@ -0,0 +1,74 @@
+use derive_more::derive::Display;
+use std::{str::FromStr, sync::LazyLock};
+use thiserror::Error;
+
+/// A version number.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Display)]
+#[display("{major}.{minor}")]
+pub struct Version {
+    /// The major part of the version.
+    pub major: u32,
+    /// The minor part of the version.
+    pub minor: u32,
+}
+
+impl Version {
+    /// The current version of the HUGR model format.
+    pub fn current() -> Self {
+        static VERSION: LazyLock<Version> = LazyLock::new(|| {
+            include_str!("../version.txt")
+                .trim()
+                .parse()
+                .expect("`version.txt` in `hugr-model` contains version that fails to parse")
+        });
+
+        *VERSION
+    }
+}
+
+impl FromStr for Version {
+    type Err = VersionParseError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let (major, minor) = s.split_once(".").ok_or(VersionParseError)?;
+        let major = major.parse().map_err(|_| VersionParseError)?;
+        let minor = minor.parse().map_err(|_| VersionParseError)?;
+        Ok(Self { major, minor })
+    }
+}
+
+/// Error when parsing a [`Version`].
+#[derive(Debug, Clone, Error)]
+#[error("failed to parse version")]
+pub struct VersionParseError;
+
+#[cfg(test)]
+mod test {
+    use super::Version;
+    use std::{hint::black_box, str::FromStr};
+
+    #[test]
+    fn test_parse() {
+        assert_eq!(
+            Version::from_str("0.1").unwrap(),
+            Version { major: 0, minor: 1 }
+        );
+        assert_eq!(
+            Version::from_str("1337.0").unwrap(),
+            Version {
+                major: 1337,
+                minor: 0
+            }
+        );
+        assert!(Version::from_str("0").is_err());
+        assert!(Version::from_str("0.").is_err());
+        assert!(Version::from_str("0.1.").is_err());
+        assert!(Version::from_str("0...").is_err());
+        assert!(Version::from_str("").is_err());
+    }
+
+    #[test]
+    fn test_current() {
+        black_box(Version::current());
+    }
+}
diff --git a/hugr-model/version.txt b/hugr-model/version.txt
new file mode 100644
index 0000000000..ba66466c2a
--- /dev/null
+++ b/hugr-model/version.txt
@@ -0,0 +1 @@
+0.0