Signals — the file-backed queue of deferred DB writes drained by the
cache-handler daemon — were produced two different ways: five call sites went
through RedisManager::setSignal() while getStreamingUserInfo inlined the same
file_put_contents(). Worse, the writer lived on RedisManager yet wrote a *file*,
not Redis — a misleading home that made the two paths look like different
transports (they were byte-identical).
Introduce XcVm\Infrastructure\Signal\SignalQueue as the single owner of the
on-disk contract (cache_<md5(key)> holding [key, data]):
- push() - the one producer API; all 7 call sites use it now
(UserRepository x4, auth.php x2, BruteforceGuard x1)
- pending() - the drain API; CacheHandlerCommand reads through it instead of its
own glob + json_decode
- pathFor() / PREFIX - path helpers
RedisManager::setSignal() stays as a thin @deprecated alias delegating to
SignalQueue::push() for any out-of-tree callers.
Behaviour unchanged (same files, same format, same consumer switch). Adds
SignalQueueTest (format / idempotency / drain / malformed). Validated live:
player_api/testxc still authenticates (auth=1) with SignalQueue autoloaded.
Verified: php -l, phpunit (435 tests, 973 assertions), make gates.
