fix(gc): one liveness rule for minor side-allocation owners; live Map stores survive in-place promotion

[proggeramlug]

Closes #12141.

During an untraced in-place promotion, the copying minor's side-allocation finalize treated every unmarked Map in the promoted blocks as dead. Untraced promotion marks nothing, so it freed the native store of live Maps, and the next map.set wrote through a NULL store. Any program whose Maps grow past about 131k entries while young blocks are promoted in place could hit it. It predates #12132.

Fix: one liveness rule

• gc/dead_owner.rs has minor_side_owner_is_dead(header, space). It returns dead only if the block is minor from-space (Eden or the active survivor half), the object is an arena object, and it is not MARKED, FORWARDED, PINNED or TENURED.
  • An in-place promotion retags its blocks as PromotedYoung before the finalize runs, so their objects are never "dead in this minor", whether the promotion was traced or untraced.
  • There is no untraced gate. Dead objects in a traced promotion are left to the old generation, and the traced test below shows the next full collection frees them.
• Every from-space finalizer and prune asks this one function: the Map walk (map/store.rs), Set, Error diagnostics, lazy JSON tapes and the address-keyed side-table prune, through the existing from-space helper. The comment at gc/copying.rs:1205 points at it.
• Behaviour change for review: promise contexts now use it too, so a pinned from-space promise keeps its context instead of having it dropped.

Tests

• test-files/test_gap_map_store_untraced_promotion.ts: four cohorts of 160k object keys, each dropping the last. It matches Node (checksum 13419760 iterated 600319825), and before the fix it crashes 3/3.
• an_untraced_promotion_keeps_the_store_of_a_live_map:
  • a rooted Map sits next to a dropped 131,100-entry Map during an untraced in-place promotion;
  • it asserts the untraced path was taken, the live Map didn't move and nothing was freed;
  • the live Map keeps its store, size and entries, and still grows and reads correctly.
• a_traced_promotion_keeps_the_live_map_and_reclaims_the_dead_one: in the traced path, the dead Map is still freed (at the next full collection).
• Negative control: with Map back on its old filter, the witness fails (2 live stores freed, 4.2 MB).
• The map_store.rs tests now use a per-thread free counter, so they are safe in parallel. map_store_survives_tenured_evacuation_sweeps_and_exit_walk and map_index_external_bytes_balance_… used to fail with 8 test threads; they now pass.

Verification

• cargo test --release -p perry-runtime -- --test-threads=1: 5221 passed, 0 failed. Main has 5219; the 2 extra are the new tests.
• Filter map promote in_place copying set, with 1 and with 8 threads, 3 runs each: all pass except ic_slow::an_unresolved_cache_slot_is_never_dereferenced, which also fails on main in debug builds only.
• The six original crash probes (200k–600k keys, string and object keys, drop and clear) all pass 3/3 with the expected output.
• cargo fmt --all -- --check is clean.

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📥 Commits

Reviewing files that changed from the base of the PR and between 52163be and ac4de60.

📒 Files selected for processing (11)

• changelog.d/12141-minor-side-owner-liveness.md
• crates/perry-runtime/src/gc/copying.rs
• crates/perry-runtime/src/gc/dead_owner.rs
• crates/perry-runtime/src/gc/mod.rs
• crates/perry-runtime/src/gc/tests/map_store.rs
• crates/perry-runtime/src/map.rs
• crates/perry-runtime/src/map/store.rs
• crates/perry-runtime/src/node_submodules/diagnostics_gc.rs
• crates/perry-runtime/src/promise/mod.rs
• crates/perry-runtime/src/set.rs
• test-files/test_gap_map_store_untraced_promotion.ts

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