fix(gc): allow retained array-growth aliases during copying verification

[proggeramlug]

Solid's effect computation can retain its sources array's original address after that tenured array grows. Perry deliberately preserves the old address as an array-growth forwarding stub, but PERRY_GC_VERIFY_EVACUATION=1 rejected this valid old-to-old alias during a copying minor.

Carry the evacuation verifier's policy through heap fields, remembered ranges, stack/global roots, mutable runtime roots, metadata, and copy-only/FFI scanners. Copying verification permits a forwarding hop only when both ends are retained array allocations; it still follows the entire chain and rejects young targets, including indirect ones. The non-copying and old-page evacuation path keeps its existing strict policy. Mutating rewrites and array access are unchanged.

The PASS1_MARKED source pin is updated after reviewing the sole cycle.rs change: selecting the strict verifier policy remains in minor finalization, outside the synchronous full-cycle census window.

Validation:

• The new old-object/array-growth regression fails on main with the same heap-field verifier panic, then passes with this fix.
• Controls exercise retained chains in four root formats and copy-only/FFI roots, and reject direct/indirect from-space references, including an unforwarded young target.
• Full runtime suite: 3,171 passed, four existing ignores (single-threaded).
• Native Solid 1.9.15 audit: all 20 output lines match Node, with four native modules and zero JavaScript modules. The original seed 4644 at rate 1 passes with evacuation verification and protected from-space: 22 copying minors, 14,022 moved objects.
• All 64 local lint/compile checks covered, including workspace Clippy and all-targets -D warnings; the two source-pin checks passed on rerun after the audit update. Two CI-only expressions are skipped by the local harness. Formatting and diff checks pass.

Follow-up to #9821; relates to #4644. This resolves the audit's verifier finding; the native UI bridge remains separate. No version bump.

Summary by CodeRabbit

• Bug Fixes

  • Fixed false evacuation-verifier aborts during copying minor garbage collection when retained array-growth references are present.
  • Improved forwarding-reference verification across chained references while continuing to reject invalid nursery references.
  • Preserved strict validation for full old-generation evacuation scenarios.

• Tests

  • Added coverage for retained array-growth aliases, multi-step forwarding chains, and invalid from-space references across supported root types.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Team

Run ID: becd980f-4790-4035-a9cc-4e3fec7061a3

📥 Commits

Reviewing files that changed from the base of the PR and between 3705978 and 350d1b4.

📒 Files selected for processing (3)

• crates/perry-runtime/src/gc/copying.rs
• crates/perry-runtime/src/gc/tests/mod.rs
• scripts/gc_runtime_root_holders.json

Included review availability: Your plan provides up to 8 included reviews per hour; 5 remain after this review.

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📝 Walkthrough

Walkthrough

Changes

Retained growth verification

Layer / File(s)	Summary
Verifier policy and forwarding traversal crates/perry-runtime/src/gc/verify.rs	EvacuationVerifier now permits retained old-generation array-growth aliases during copying-minor verification while rejecting stale from-space references.
Verifier wiring and root scanning crates/perry-runtime/src/gc/roots.rs, crates/perry-runtime/src/gc/copying.rs, crates/perry-runtime/src/gc/cycle.rs, crates/perry-runtime/src/gc/tests/runtime_roots/*	Verification paths now receive configured copying-minor or all-forwarded verifiers.
Minor collection diagnostics crates/perry-runtime/src/gc/copying.rs	Optional survival diagnostics now record worklist, promotion, drain, and remembered-set information during minor collection.
Forwarding coverage and audit updates crates/perry-runtime/src/gc/tests/forwarding_verification.rs, crates/perry-runtime/src/gc/tests/mod.rs, changelog.d/9822-retained-growth-verifier.md, scripts/gc_runtime_root_holders.json	Tests cover retained aliases, forwarding chains, root formats, heap slots, and from-space rejection. The changelog and audit metadata are updated.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: ⚪ Minimal · up to 350d1

This change permits valid retained array-growth aliases during copying minor GC while retaining rejection of stale from-space references and strict verification elsewhere. The supplied coverage indicates no remaining merge-blocking risk.

Sequence Diagram(s)

sequenceDiagram
  participant CopyingMinorGC
  participant EvacuationVerifier
  participant RuntimeRootVisitor
  participant HeapObjectVerifier
  CopyingMinorGC->>EvacuationVerifier: create copying_minor verifier
  CopyingMinorGC->>RuntimeRootVisitor: verify runtime roots
  RuntimeRootVisitor->>EvacuationVerifier: inspect forwarded references
  CopyingMinorGC->>HeapObjectVerifier: verify heap fields
  HeapObjectVerifier->>EvacuationVerifier: inspect forwarded references
  EvacuationVerifier-->>CopyingMinorGC: accept retained alias or report stale reference

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Suggested reviewers: jdalton

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 47.37% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 38 functions across 8 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely identifies the main change: allowing retained array-growth aliases during copying verification.
Description check	✅ Passed	The description explains the problem, implementation scope, preserved behavior, related issues, and detailed validation results. It does not reproduce the template headings or checklist items, but it …
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.

Full details: Docstring Coverage

Explanation

Docstring coverage is 47.37% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 38 functions across 8 files. (1 skipped: 1 unsupported.)

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✨ Finishing Touches

🧪 Generate unit tests (beta)

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[proggeramlug]

Landed on main via merge train #9866 (rebase-merged, so your commits keep their authorship). Thanks!