Document LazyLock race-safety coverage (#342)

[lodyai]

Summary

This branch clarifies that the existing parallel thematic-break test is
application-level regression coverage for the standard library's LazyLock
race-safety guarantee. It names the test after that guarantee and records why
the coverage is retained instead of duplicating the standard library's own
tests.

Closes #342.

Review walkthrough

• Start with src/breaks.rs to review the clarified test name and regression-coverage rationale. The existing 16-thread barrier, borrowed-value checks and pointer-identity assertions remain unchanged.

Validation

• make check-fmt: passed
• make lint: passed
• make test: passed, including lazylock_initialisation_is_race_safe
• coderabbit review --agent: passed with zero findings after the required rate-limit back-off

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: cd3e7a39-75fd-4fca-9bb3-ba007b25c3eb

📥 Commits

Reviewing files that changed from the base of the PR and between ad3bfd1 and ba27da4.

📒 Files selected for processing (1)

• src/breaks.rs

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Summary

• Renamed the parallel thematic-break regression test to lazylock_initialisation_is_race_safe.
• Documented that it provides application-level coverage while relying on the standard library’s LazyLock race-safety guarantee.
• Preserved the existing 16-thread barrier, borrowed-value checks, and pointer-identity assertions.
• No production logic or public APIs changed.

Walkthrough

Rename the concurrent thematic-break test to describe LazyLock initialisation race safety and document its reliance on the standard library guarantee. Production logic and public APIs remain unchanged.

Changes

Race-safety test coverage

Layer / File(s)	Summary
Document LazyLock race-safety coverage src/breaks.rs	Rename the multi-threaded test and add a comment documenting the standard library’s race-safety guarantee; retain the existing barrier and assertions.

Suggested labels: Issue
Suggested reviewers: leynos

Poem

Threads gather, then align,
LazyLock guards the line,
One init, safely won,
Tests explain what’s done.

🚥 Pre-merge checks | ✅ 20

✅ Passed checks (20 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title matches the documented LazyLock race-safety coverage change and correctly references issue #342.
Description check	✅ Passed	The description stays on topic and accurately describes the test rename and rationale change.
Linked Issues check	✅ Passed	The PR satisfies #342 by retaining concurrent-access coverage and documenting the stdlib LazyLock guarantee.
Out of Scope Changes check	✅ Passed	No out-of-scope changes are present; the diff only touches the related test name and documentation comment.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Testing (Overall)	✅ Passed	No production behaviour changed; the retained thread test still fails if format_breaks stops borrowing the shared break line or returns owned strings.
User-Facing Documentation	✅ Passed	PASS: The PR only renames a test and adds an internal comment; no user-facing functionality or behaviour changed, so no users-guide update is required.
Developer Documentation	✅ Passed	Pass: leave docs untouched; no API, architecture, tooling, or roadmap change landed, and existing docs already cover the shared LazyLock behaviour.
Module-Level Documentation	✅ Passed	src/breaks.rs already has a top-level //! module docstring, and this PR only changes a test name/comment, not module documentation.
Testing (Unit And Behavioural)	✅ Passed	Accept the renamed concurrency test: it exercises the public format_breaks boundary and verifies the borrowed-static invariant under parallel calls.
Testing (Property / Proof)	✅ Passed	PASS: The PR only renames a test and adds a comment; no new invariant or proof obligation is introduced, and proptest coverage for format_breaks already exists.
Testing (Compile-Time / Ui)	✅ Passed	Only a runtime test rename/comment changed; no compile-time behaviour or UI/text output was introduced, so trybuild/snapshot coverage is not applicable.
Unit Architecture	✅ Passed	Keep the change test-only: it renames a #[cfg(test)] race-safety regression test and adds a comment; no query, command, dependency, or side-effect boundaries changed.
Domain Architecture	✅ Passed	Only a test name and comment changed in src/breaks.rs; production code and the domain model are untouched, so no boundary leak appears.
Observability	✅ Passed	Alteration is test-only: the diff renames a race-safety test and adds a comment, with no production logging, metrics, tracing, or alerts added.
Security And Privacy	✅ Passed	Approve it: the only change is a test rename plus a benign comment, with no secrets, credentials, trust-boundary changes, or sensitive-data exposure.
Performance And Resource Use	✅ Passed	Only a test rename and comment changed; no production path, allocations, loops, or I/O were altered, and the existing 16-thread test stays bounded.
Concurrency And State	✅ Passed	Accept it: the patch only renames an existing 16-thread LazyLock race-safety test and adds a comment; no shared-state behaviour changed.
Architectural Complexity And Maintainability	✅ Passed	PASS: Keep the change scoped to a test rename and comment; introduce no new abstractions, layers, or dependencies, and leave production code untouched.
Rust Compiler Lint Integrity	✅ Passed	src/breaks.rs only renames a test and adds a comment; no new lint suppressions, dead-code hacks, or extra clone calls were introduced.

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View plan for ticket: #342

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch issue-342-concurrency-test-for-thematic-break-lazylock-init

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