unit_keys_from now resolves the Media Key in order: stored per-disc MK
-> keydb Processing Key pool (mk_from_pk vs this disc's own MKB) ->
device-key pool (mk_from_dk), then MK+VID -> VUK -> UK. MK/VUK entries
still honored directly; cross-disc MK-pool brute stays retired. Fixes the
factually-wrong justifying comment + adds PK-pool KATs.
Add tests/key_sources.rs exercising the published KeySource impls
end-to-end over real fixture files and the libfreemkv parsers:
- KeydbSource: disc-hash lookup from a real keydb.cfg (VUK hit ranks
ahead of the universal DK pool), hash miss yields only the pool,
missing file is silent/not errored, label + needs_samples, and
host-cert serving from a | HC | row (inherent and trait paths).
- paths: exe-local search list, default == search head, existing path
reflects on-disk state (local-only, no OS fallback).
- MapfileSource: persisted # freemkv-uk: keys read back as a terminal
Key::Unit, one-shot exhaustion, missing/keyless mapfile offers nothing.
- OnlineSource: unconfigured no-op (no network), one-shot latch,
metadata, and validate_keyserver_url scheme/SSRF gating.
- MultiSource: caller-supplied order/precedence (and its reverse),
empty-source skip, needs_samples/errored OR-aggregation, nesting, and
a real keydb-then-mapfile precedence chain over fixtures.
Matthew Jackson