ci: prove current PCEA release artifact on Node-24 Actions

[erinepshovel-code]

Replacement for stale release-readiness work in #36

Built from current main@9f3168e385d69922aa9b12882f673eb6b4484ec1, where PCEA is already version 0.2.0 and mutable PCEA research has been moved to stack/research/pcea/.

Change

• replace Node-20-generation actions/checkout@v4 / setup-python@v5 with published @v6 in both active workflows;
• expand the contract-boundary job to the full repository pytest suite on Python 3.9, 3.11, and 3.13;
• add permissions: contents: read;
• build the declared wheel, install it into a clean venv outside the source tree, verify installed metadata version against pyproject.toml, and smoke-test the public package surface.

Not carried from #36

The ratcheted session, arity experiments, candidate-ledger edits, and other mutable pcea-ucns research are intentionally not reintroduced after the stable/research separation.

Verification

Repository CI on this PR is authoritative.

hmmm

Independent cryptographic/security review remains separate from repository packaging and CI correctness.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-01T12:42:05.663946Z	b14df3f	New commits

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 40127a5513

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".