Two correctness bugs in multi-process cluster mode (m8p10), both found live on a
real 3-pod k3s cluster while validating the deployment, both invisible to the
existing in-process / unauthenticated test suites:
1. Forwarded item/embedding writes dropped on the floor. create_item /
write_embedding gated the leader's peer broadcast on `if internal { return }`.
A write to a NON-leader gateway is forwarded to the leader with the internal
marker set (loop-prevention), so it hit that branch and terminated WITHOUT
broadcasting — the item landed only on the leader. Signals were unaffected
(the WAL relay ships regardless of the marker), which masked it. Fix: gate on
leadership, not the marker — a follower applying a marked broadcast/heal
terminates; the leader (external OR forwarded) always fans out. Forwarded
writes now return the {replicated_to,failed} report instead of a bodyless null.
2. Heal item/embedding backfill 401'd whenever TIDAL_API_KEY is set.
post_marked_blocking sent the internal marker but no Authorization header. The
marker is a trust signal, not an auth bypass (the bearer middleware runs
first), so every backfill POST was rejected 401 — a region that missed an item
while down stayed permanently inconsistent at lag 0. Unauthenticated tests
never caught it. Fix: thread TIDAL_API_KEY into RegionClusterState and attach
it (same key on every region) to the backfill POSTs.
Verified live: forwarded writes via follower gateways converge to all 3 regions;
a region scaled to 0 during an item write backfills on heal (item_failures=0).
Follow-up: add multiproc regression tests with auth for both paths.
6f17409f40