Add a per-remote mirror_strategy selector for the mirrorlist, supporting
round_robin (default, unchanged) and least_conn.
- models.Remote gains MirrorStrategy string + MirrorStrategy{RoundRobin,LeastConn}
constants and ValidateMirrorStrategy (enum check; least_conn requires a
non-empty mirrorlist). Empty behaves as round_robin for back-compat.
- DB: additive mirror_strategy TEXT NOT NULL DEFAULT 'round_robin' column
(CREATE TABLE + ADD COLUMN IF NOT EXISTS), wired through remoteCols/scanRemote/
CreateRemote/UpdateRemote; empty normalized to round_robin on write.
- Engine: least_conn starts each attempt with the pool URL holding the fewest
in-flight requests via a per-remote/per-URL atomic gauge (incremented around
each upstream call in head/fetch/checkUpstream), ties broken by the existing
round-robin rotation. Round-robin path and failover order unchanged;
single-URL pools are a no-op.
- Tests: unit tests for least-loaded selection, round-robin default, gauge
inc/dec, single-URL no-op, and strategy validation; DB round-trip covers the
new column; docker e2e adds a least_conn distribution test and a real dnf
install through a least_conn remote.
unkin-agent