Extends MediaServerReconciliationGuard (#477) with a second deterministic refusal: when the
enumeration that produced the incoming set silently dropped items whose projection THREW, the
file-not-found sweep is refused. A dropped item the server did return is indistinguishable
from a deletion at the reconcile step, so a projection regression could otherwise mass-flag a
healthy library FileNotFound (which EmptyTrash then deletes permanently).
Deliberate guard-clause skips (STRM files, virtual items, unsupported types) are explicitly NOT
failures and never suppress a sweep — counting them would permanently disable reconciliation for
any library holding a single STRM file.
The ratio / missing-fraction threshold is REJECTED, not deferred: it is a two-sided heuristic
with no tunable default and no telemetry, and the failure it approximates is exactly observable
via the projection-failure count (a genuine bulk deletion produces zero failures).
Seam is deliberately narrow — the private ProjectTo* contract inside each api client changed from
Option<T> to MediaServerProjectionResult<T> (projected/skipped/failed), the paged helper counts
IsFailure in one place, and the scanner reads it through an optional trailing
MediaServerProjectionFailureCounter on only the five library-level methods that feed a sweep.
The counter is per-enumeration state created by the scanner, never a field on an api client.
fixes#484
timothy
e3645a2840