Document mutation-testing workflow contract tests

[leynos]

Summary

Adds a ## Mutation-testing workflow contract tests section to
docs/developers-guide.md, documenting the informational mutation-testing
caller workflow (.github/workflows/mutation-testing.yml, which delegates to
leynos/shared-actions/.github/workflows/mutation-cargo.yml) and the pytest
contract test at tests/workflow_contracts/mutation_testing_test.py that
pins its shape.

The section is placed immediately after the existing "Workflow pins and
Dependabot" section, since it documents a concrete application of that
general shape-only pinning policy, rather than as a new detached top-level
section.

Details

• Permutation: Rust workspace (weaver's crates live under crates/,
  with no root src/; the caller mutates the whole workspace on manual
  dispatch, using --test-workspace=true so mutants also face dependent
  crates' tests).
• Contract-test style: the uses: pin is asserted shape-only (USES_RE
  matches ...@[0-9a-f]{40}, no hard-coded SHA — Dependabot bumps freely).
  The with: block, by contrast, is asserted for exact equality against an
  EXPECTED_WITH dict, so any change to paths, exclude-globs, or
  extra-args requires an accompanying test edit. There is no
  pytestmark = pytest.mark.skipif(...) guard on the module — unlike a
  mutmut-based Python repo, weaver's mutation runner is cargo-mutants, so
  there is no sandbox that omits .github/.
• Local run command documented: make test-workflow-contracts (exists
  in the Makefile and simply invokes
  uv run --with 'pytest>=8' --with 'pyyaml>=6' pytest tests/workflow_contracts -q).
• Roadmap/execplan tracking: none applies. docs/roadmap.md and
  docs/execplans/* only mention "mutation" in the sense of Weaver's own
  code-mutation/refactor commands, not mutation-testing CI infrastructure.
  No task was ticked or annotated.
• TOC/cross-link: docs/developers-guide.md has no internal
  section-level table of contents to update. The top-level docs/contents.md
  index already links the whole file (- [Developer's guide] (developers-guide.md)), so no additional cross-link was needed.
• Docs-lint result: make markdownlint passes (spelling gate, coverage
  gate, and markdownlint-cli2 all clean). Two -ise spellings copied from
  a draft template (summarising, serialises) were caught by the spelling
  gate and corrected to -ize per this repository's oxendict policy before
  the gate passed.

File changed

• docs/developers-guide.md

Test plan

• make markdownlint (spelling + markdownlint-cli2) — passes
• Rust/Python test suites — intentionally not run; this is a docs-only
  change per the task brief

[sourcery-ai]

Sorry @leynos, you have reached your weekly rate limit of 500000 diff characters.

Please try again later or upgrade to continue using Sourcery

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 139fd9d3-a371-4f9b-9f7f-91b72e4c212d

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch docs/mutation-contract-tests

---

_{Comment @coderabbitai help to get the list of available commands.}

[codescene-access]

No quality gates enabled for this code.