cargo clippy fails: non-exhaustive match on nbformat::Notebook (missing V3 arm) in NotebookVfs

[AttilaMihaly]

Summary

cargo clippy --package morphir --all-targets -- -D warnings fails to compile morphir-common with:

error[E0004]: non-exhaustive patterns: `nbformat::Notebook::V3(_)` not covered
  --> crates/morphir-common/src/vfs/notebook.rs:23:33
   |
23 |         let v4_notebook = match notebook {
   |                                 ^^^^^^^^ pattern `nbformat::Notebook::V3(_)` not covered

NotebookVfs::from_notebook (crates/morphir-common/src/vfs/notebook.rs:20-38) matches on nbformat::Notebook with arms for V4 and Legacy only.

Root cause

Cargo.toml pins nbformat = "1.0" (i.e. ^1.0, any 1.x). The committed Cargo.lock in this repo resolves that to 1.0.0, where Notebook only has V4/Legacy variants, so the match is exhaustive as committed and cargo build/cargo test against the locked versions pass fine.

The bug is latent rather than absent: nbformat has since published 1.2.2, which adds a Notebook::V3 variant. Anything that re-resolves the lockfile against the current registry (a fresh cargo generate-lockfile, cargo update, or a consumer with a looser lock) picks up 1.2.2 and the match stops being exhaustive.

Where this actually bit us

In the parent finos/morphir monorepo, the morphir CLI CI job runs prepare_cli_workspace.py before building, which deletes Cargo.lock and runs cargo generate-lockfile fresh (to build the CLI-only workspace without morphir-live). That resolves nbformat to 1.2.2 and the job fails on this exhaustiveness check.

This is currently blocking otherwise-unrelated PRs in finos/morphir — confirmed via finos/morphir#626, which only touches .github/workflows/*.yml (no Rust/Cargo changes at all) and still hits this exact error, since it's the CI job's fresh lockfile resolution surfacing a pre-existing gap in this repo's code, not anything introduced by that PR. See the failing run: https://github.com/finos/morphir/actions/runs/32068606383/job/95506448404

Also affects finos/morphir#638 and finos/morphir#612.

Suggested fix

Add a Notebook::V3(_) arm to the match in notebook.rs, analogous to how Legacy is currently handled (falls back to an empty v4::Notebook) — or implement an actual V3→V4 conversion if that's preferable. A todo!()/unimplemented!() stub would compile but just move the failure to runtime, so real handling (even if it's "unsupported, return an error") is preferable to silence clippy.

Alternatively/additionally, consider whether nbformat = "1.0" should be tightened (e.g. "~1.0" or exact-pinned) so a routine lockfile regeneration doesn't silently pick up a semver-compatible release that adds unhandled enum variants.