fix(multiplayer): reconcile authoritative initial connections

server/migrations/0010_initial_connect_ready_at.sql

@@ -0,0 +1,13 @@
+ALTER TABLE matches
+    ADD COLUMN initial_connect_ready_at TIMESTAMPTZ;
+
+-- Existing in-flight matches receive a fresh, fair connection window when
+-- this migration is deployed. Future rows are stamped by the transition to
+-- ASSIGNMENT_READY, not by match creation or provider allocation.
+UPDATE matches
+SET initial_connect_ready_at = now()
+WHERE state IN ('ASSIGNMENT_READY', 'ASSIGNED', 'CONNECTING');
+
+ALTER TABLE matches
+    ADD CONSTRAINT matches_initial_connect_ready_at
+    CHECK (state NOT IN ('ASSIGNMENT_READY', 'ASSIGNED', 'CONNECTING') OR initial_connect_ready_at IS NOT NULL) NOT VALID;