gc: CONSOLE_INSTANCES is a rekeyed address-keyed table with no dead-key prune

[proggeramlug]

CONSOLE_INSTANCES (crates/perry-runtime/src/builtins/console.rs) is keyed by the raw heap address of the console instance object (js_object_alloc(CONSOLE_INSTANCE_CLASS_ID, 0) as usize, console.rs:1037-1049) and its key is rekeyed by scan_console_log_singleton_roots_mut (console.rs:210, visit_metadata_usize_slot) — rewritten if the object moved, deliberately not marked.

Nothing tells the table when that object dies. It is absent from gc::dead_owner's DEAD_KEY_PRUNES fan-out and from gc_type_clear_dead_payload_side_tables; the only other uses are lookups at console.rs:960/1039.

That is the #8040 shape. A dead key is not merely a leak for a rekeyed table: the arena recycles the address, the recycled bytes are read as a GcHeader, and a coincidental GC_FLAG_FORWARDED byte makes the rewrite pass follow a garbage forwarding pointer. #8174 narrowed what can be followed out of such a header; it did not remove the dead key.

Fix: add a prune_dead_console_instance_owners and wire it into DEAD_KEY_PRUNES in crates/perry-runtime/src/gc/dead_owner.rs, with a dead_owner_side_tables.rs case.

Declared as open_gap in scripts/gc_rekeyed_key_tables.json; closing this must delete that entry, or the gate fails on the stale exemption.

Refs #8174, #8168, #8040.

[proggeramlug]

Fixed in #8196.

The #8174 registry gate enumerated every visit_metadata_* rekey site and required a written verdict for each; this table had none, and rather than declare it an exemption the prune is wired in. Its entry in scripts/gc_rekeyed_key_tables.json now names a registered DEAD_KEY_PRUNES member, and MAX_OPEN_GAPS is 0 — the manifest ships with no declared gaps at all.

Covered by a pair of cases in gc/tests/dead_owner_side_tables.rs: the prune fires (dead owner, one collection, the table observably shrinks) and its inverse (a rooted owner's entry survives).

Independent evidence that these were real stale keys and not a theoretical hazard: with only #8174's forwarding-target discriminators in place and none of these prunes, the production Next App Route forced-evacuation workload logged 988 [gc-forwarding] refused_sources events — stale forwarding headers reaching a rewrite walk. With the six prunes in, the same workload logs 0 across 458 copying minors and 182,977 copied objects.