Fixes #2988 .

This makes all the guppylang tests pass again. (Many were broken by
#2973 .)

It would be good to add a test case local to hugr; I will work on that,
but propose merging this as is since it fixes a critical issue.

## 🤖 New release

* `hugr-model`: 0.26.1 -> 0.27.0 (✓ API compatible changes)
* `hugr-core`: 0.26.1 -> 0.27.0 (✓ API compatible changes)
* `hugr-llvm`: 0.26.1 -> 0.27.0 (✓ API compatible changes)
* `hugr-persistent`: 0.5.1 -> 0.6.0 (✓ API compatible changes)
* `hugr`: 0.26.1 -> 0.27.0 (✓ API compatible changes)
* `hugr-cli`: 0.26.1 -> 0.27.0 (✓ API compatible changes)

<details><summary><i><b>Changelog</b></i></summary><p>

## `hugr-model`

<blockquote>

##
[0.26.0](hugr-model-v0.25.7...hugr-model-v0.26.0)
- 2026-03-16

### Testing

- Replace model text snapshots with roundtrip tests
([#2933](#2933))
- Add missing width arg in model-call example
([#2945](#2945))
</blockquote>

## `hugr-core`

<blockquote>

##
[0.27.0](hugr-core-v0.26.1...hugr-core-v0.27.0)
- 2026-03-31

### Bug Fixes

- Use valid identifiers when constructing AST model
([#2973](#2973))
- Panic on constant folding with opaque consts
([#2986](#2986))

### New Features

- *(py)* Allow missing ext versions ExtensionDesc metadata
([#2979](#2979))
- [**breaking**] Deprecate JSON serialization format
([#2991](#2991))
- [**breaking**] Bump public `portgraph` dependency to `0.16.0`
([#2998](#2998))

### Refactor

- Simplify validate_subtree
([#2969](#2969))
- further cleanups to SiblingSubgraph + generalize over trait
HugrConvexChecker
([#2957](#2957))
</blockquote>

## `hugr-llvm`

<blockquote>

##
[0.27.0](hugr-llvm-v0.26.1...hugr-llvm-v0.27.0)
- 2026-03-31

### New Features

- *(hugr-llvm)* Emit rounding operation for `FloatOps::fround` extension
ops ([#2949](#2949))
</blockquote>

## `hugr-persistent`

<blockquote>

##
[0.6.0](hugr-persistent-v0.5.1...hugr-persistent-v0.6.0)
- 2026-03-31

### New Features

- [**breaking**] Deprecate JSON serialization format
([#2991](#2991))
</blockquote>

## `hugr`

<blockquote>

##
[0.27.0](hugr-v0.26.1...hugr-v0.27.0)
- 2026-03-31

### Bug Fixes

- Use valid identifiers when constructing AST model
([#2973](#2973))
- Panic on constant folding with opaque consts
([#2986](#2986))

### New Features

- *(py)* Allow missing ext versions ExtensionDesc metadata
([#2979](#2979))
- [**breaking**] Bump public `portgraph` dependency to `0.16.0`
([#2998](#2998))
- [**breaking**] Deprecate JSON serialization format
([#2991](#2991))

### Refactor

- Simplify validate_subtree
([#2969](#2969))
- further cleanups to SiblingSubgraph + generalize over trait
HugrConvexChecker
([#2957](#2957))
</blockquote>

## `hugr-cli`

<blockquote>

##
[0.27.0](hugr-cli-v0.26.1...hugr-cli-v0.27.0)
- 2026-03-31

### Bug Fixes

- Do extension resolution on exts loaded by hugr-cli
([#2987](#2987))

### New Features

- *(py)* Allow missing ext versions ExtensionDesc metadata
([#2979](#2979))
- [**breaking**] Deprecate JSON serialization format
([#2991](#2991))
</blockquote>


</p></details>

---
This PR was generated with
[release-plz](https://github.com/release-plz/release-plz/).

---------

Co-authored-by: Agustín Borgna <[email protected]>

🤖 I have created a release *beep* *boop*
---


##
[0.16.0](hugr-py-v0.15.4...hugr-py-v0.16.0)
(2026-04-01)

This release changes the default text serialization format from JSON to
`MODEL_WITH_EXTS` (the JSON format is now deprecated).
It also adds the ability to link packages and modules from Python,
renders operation type arguments in HUGR visualizations, introduces a
new `debug_info` module for attaching source-level debug metadata to
nodes,
and introduces multi-version support in `ExtensionRegistry`, allowing
different versions of the same extension to coexist in the same
registry.


### ⚠ BREAKING CHANGES

* `ExtensionRegistry` may now contain multiple versions of the same
extension. `.extensions` is now an iterator of the latest versions
instead of a dictionary. `.register_updated` and `.add_extension` have
been replaced with a singular `.register`.
* Default `EnvelopeConfig` changed from `EnvelopeFormat.JSON` to
`EnvelopeFormat.MODEL_WITH_EXTS`.
* Substituted `hugr-py/src/hugr/tys.py::_type_str` with
`hugr-py/src/hugr/utils.py::name_w_args`.

### Features

* Add debug info metadata specification in `hugr-py`
([#2971](#2971))
([a4da8ef](a4da8ef))
* Allow multiple versions of an extension in an ExtensionRegistry
([#3005](#3005))
([ee90cd1](ee90cd1))
* Deprecate JSON serialization format
([#2991](#2991))
([0f7a880](0f7a880))
* Operation parameter rendering in HUGR visualizations
([#2995](#2995))
([d619148](d619148))
* Allow linking packages and modules from Python
([#2947](#2947))
([329c243](329c243))
* Make `_composable_pass` and `_scope` public modules
([#2962](#2962))
([1d6af9a](1d6af9a)),
closes [#2961](#2961)
* Allow missing ext versions ExtensionDesc metadata
([#2979](#2979))
([bc1c445](bc1c445))
* Allow dfg conversion in to TrackedDfg
([#2993](#2993))
([3bd7a88](3bd7a88))


### Bug Fixes

* Allow both _composable_pass and composable_pass imports
([#2965](#2965))
([0a5664d](0a5664d))
* Allow both _scope and scope imports
([#3003](#3003))
([de0458c](de0458c))
* Always do extension resolution when loading packages and hugrs
([#2953](#2953))
([0086d2a](0086d2a))
* Correct pyo3 module definitions and add missing exception class export
([#2964](#2964))
([3df73f4](3df73f4))
* Include extensions during link serialization
([#2992](#2992))
([9236e89](9236e89))
* Prefix names with underscores during serialization
([#2989](#2989))
([8aab636](8aab636))
* Use valid identifiers when constructing AST model
([#2973](#2973))
([8750a6b](8750a6b))

---
This PR was generated with [Release
Please](https://github.com/googleapis/release-please). See
[documentation](https://github.com/googleapis/release-please#release-please).

---------

Co-authored-by: Agustín Borgna <[email protected]>