[284km]

Repeated collections compact every live string page even when no string on it has changed. Track mutations separately from byte-accounting dirtiness and skip pages whose changed storage has already been reclaimed. Completely dead pages still return to the pool.

The compiler returns unit even when a native pin defers compaction. Clear the mutation flag only when the page capacity decreases after the call; deferred and equal-capacity compactions conservatively remain pending. Runtime retirement continues to reclaim old arenas globally.

Validation:

• The production compaction helper is compiled with the pinned compiler in a native regression. Forced pins exercise both native early-return paths; releasing the pin without another page write then reclaims more than 8 MiB down to 4 KiB and preserves the live value. This passed on macOS and Linux and runs in both CI jobs.
• Ruby coverage for unchanged pages, old-page mutations, binary and empty strings, suspended iteration, and page reuse matches Ruby 4.0.9 with hash indexing ON/OFF, normally and under GC stress.
• A benchmark keeps 20,000 strings across 20 collections and validates every value before and after mutation. Two local O2 runs changed the timed collection section from 0.057–0.058 seconds on Release completed statement temporaries before exit-hook workloads #35 to 0.035–0.039 seconds after this change. These are workload timings, not an end-to-end CI measurement.

The full Unicode file completes in 431 seconds under the unchanged 600-second limit: 422 tests and 1,831,104 assertions. All 64 failures and 4 errors match the baseline reports exactly. The combined #32–#36 implementation on main f7ee263 passes all 515 corpus programs with hash indexing ON and OFF; its Unicode run completes in 423 seconds with identical baseline failure/error reports. New-head CI is in progress.

CI for this head passed all 29 jobs. All 758 CRuby test files were collected from 8 shards with no missing files or infrastructure errors. This confirms complete measurement, not full Ruby conformance. The local integration of #32–#36 with main f7ee263 also passed all 515 corpus programs with hash indexing ON and OFF. The full Unicode suite completed within the unchanged limit with the same 68 baseline failure/error reports. The TCP regressions and native compaction-deferral checks also passed.

[284km]

Reviewed e925f72 against its stacked base a4eb486 (#35). Found one Major issue: the mutation bit is cleared even when the native Vec runtime defers compaction. Once the pin is released, an otherwise unchanged page no longer gets retried, retaining overwritten storage until a later write. Please address this before merging.

Separating mutation tracking from byte-accounting dirtiness is appropriate, and the Ruby value regressions passed. The finding concerns reclamation after a deferred native compaction; details and a suggested regression are inline.

Validation:

• Fresh O2 head build with the CI-pinned Mere 991f299b compiler and mgz revision; compared with the existing O2 build of the exact #35 base.
• The new regression matched Ruby 4.0.9 on both revisions with indexing ON/OFF, normally and with MERE_RUBY_GC_STRESS=100 (eight runs).
• Five related corpus programs covering collections inside methods, suspended Fiber values, string-page reuse, collected handles, and exit roots matched Ruby on the head with indexing ON/OFF (ten runs).
• A controlled native contract test using the exact generated Vec runtime and a forced pin predicate confirmed that vec_compact can return without changing the arena. Applying the new flag-clearing logic retained 8,392,720 bytes after unpinning; an unconditional retry reduced the page to 4,096 bytes. This isolates the runtime contract rather than claiming a measured Ruby-level leak from the supplied corpus.
• Two default benchmark runs per revision matched Ruby's stdout. Timed collections were 0.044–0.054 s on #35 and 0.0322–0.0324 s on the head. Other validation ran concurrently; these are local workload measurements.
• CI for this exact head reports 510/510 corpus programs matching Ruby and a successful Linux build. Broader jobs remain pending. I did not repeat the entire corpus, Linux validation, or Unicode measurements locally.
• git diff --check passed.

[284km]

Re-reviewed 8c85dd5 against the previously reviewed e925f72, retaining #35 as the stacked base. The previous Major finding is resolved. No new actionable findings.

The page's mutation flag is now cleared only when the production helper observes a strict capacity decrease. Native pin deferrals and equal-capacity copies conservatively remain pending, so a later collection can retry without another page write. This is compatible with the pinned compiler's unit-returning compaction API; equal-capacity copies may still be retried, as documented.

Validation:

• Fresh O2 build with the pinned Mere 991f299b compiler and mgz revision.
• unittest/string_page_compact_check.py passed using the actual production helper and generated runtime: both native early-return paths preserve pending work, unpinning reclaims the overwritten 8 MiB down to 4 KiB, and the live value remains intact.
• The string-page corpus regression matched Ruby 4.0.9 with indexing ON/OFF, normally and with MERE_RUBY_GC_STRESS=100.
• Related collected-handle and #35 exit-root regressions matched Ruby in both index modes.
• CI for this exact head reports 510/510 corpus programs matching Ruby and a successful Linux build. Broader jobs remain pending.
• git diff --check passed.

The deferred-compaction finding can be considered addressed. Full corpus, Linux execution, Unicode-suite timings, and benchmarks were not repeated locally.