Root cause of soak20 signature 2 (refcount_test.exs 'watcher crash',
110235x fast {:error, :server_down} probes over the full await window):
by_name mapped name -> slot *index*, so a name whose holder died (no stop
path unregisters; prune is lazy) and whose slot was then re-tenanted read
as live-held: register failed NameTaken{holder: <unrelated tenant>} (which
the bridge macro's generated start() swallows -> start_server/1 reports :ok
for a server that never came up), while name resolution reached the
tenant's mailbox, missed on the message TypeId and failed fast WITHOUT
pruning — the wedge self-sustained for the tenant's lifetime. Name-
addressed send additionally judged liveness on the slot's *current*
mailbox pid, so a same-typed tenant would have received the message
(misdelivery) and a differently typed one a misleading NoChannel.
Fix: by_name: HashMap<&'static str, Pid> — every reader judges the
*stored* holder with the generation-checked live(), so a recycled slot's
tenant no longer impersonates a dead holder, and every touch (register /
whereis / resolve / send) prunes and heals a stale name. prune(index)
becomes prune_holder(pid): names bound to the holder go; the mailbox goes
only while still the holder's own (a tenant's replacement mailbox is left
untouched). Introspection matches names to mailboxes by full pid, so a
stale name never annotates a slot's new tenant.
Deterministic regression test added first and shown to fail pre-fix
(tests/stale_name_slot_reuse.rs: tiny slab forces re-tenanting; old slot
(1,0) died, tenant (1,1) took the index; register -> NameTaken pre-fix).
Post-fix it asserts the healed contract: whereis -> None (pruned), call ->
ServerDown, re-register -> Ok. Suite 33 ok-binaries, clippy gate clean.
In the wild the window opened at every splice_test teardown:
Splice.terminate -> exit_server('subtree') left the name bound; width 20
raised the re-tenant probability. Downstream (smarm_beam): install_child's
unregister-before-register workaround becomes dead code (removed there);
the #[smarm_server] macro's swallowed register error becomes truthful
idempotency (a NameTaken now really is a live holder).
