docs(gc): the copy-slot-hoists tests cover one hoist, not two (#10388)

[proggeramlug]

Addresses CodeRabbit's review comment on #10388, which landed before the comment was acted on.

gc/tests/copy_slot_hoists.rs opened by claiming the copying minor hoists two per-parent facts (weak holder and old generation), each pinned by a sabotaged twin. Only the weak-holder fact landed, and the file contains exactly one test pair for it. The old-generation hoist was deliberately left out of #10388 because no sabotage of it could be made to fail (sticky dirty-page coverage carries the old→young edge independently of the remembered-set re-insertion that fact controls).

A test header that claims coverage the file does not have is worse than no header: the next reader assumes the generation hoist is witnessed. This rewrites the header to describe the one hoist that is tested, and records why the other one is absent, so it is not re-added on the strength of a test that does not exist.

Comment-only change to a test module; no code, behaviour or generated output changes. skip-changelog per changelog.d/README.md.

Summary by CodeRabbit

• Documentation
  • Clarified documentation for weak-holder fact hoisting.
  • Documented that old-generation facts are not hoisted and explained why no corresponding witness test is included.
  • Recorded separate coverage for sticky dirty-page behavior and its related issue reference.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: bafb270c-b2e1-4d9d-bf59-e9d7e3ce0c09

📥 Commits

Reviewing files that changed from the base of the PR and between e6dcb62 and ef58242.

📒 Files selected for processing (1)

• crates/perry-runtime/src/gc/tests/copy_slot_hoists.rs

Included review availability: Your plan provides up to 8 included reviews per hour; 6 remain after this review.

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📝 Walkthrough

Walkthrough

The module documentation now describes only the weak-holder fact hoist. It explains the absence of an old-generation witness test and identifies independent sticky dirty-page coverage.

Changes

GC Documentation

Layer / File(s)	Summary
Hoist behavior documentation crates/perry-runtime/src/gc/tests/copy_slot_hoists.rs	The documentation removes the old-generation hoist claim, explains why no corresponding sabotage witness exists, and records independent sticky dirty-page coverage.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~3 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to ef582

This documentation-only update introduces no concrete production or test-execution risk and is mergeable.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the documentation change and accurately states that the tests cover one hoist, not two.
Description check	✅ Passed	The description clearly explains the change, rationale, scope, related issue, and absence of behavior changes. It does not use the required section headings and does not provide the template's test-pl…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[proggeramlug]

Landed via merge train #10413 (v0.5.1588). All source commits preserve authorship; merged main matches the validated train exactly.