MountEligibilityAssets class

Injects grid_assets mount eligibility into the ambient service bundle.

Eligible snapshots pass through synchronously. A refused snapshot starts one scoped fresh FILING read; while it is in flight the refusal stays LOUD, and completion re-provides the bundle with either the fresh decision or a refusal that names the read failure. The read is BOUNDED by kMountEligibilityReadDeadline so "in flight" always ends: a store that never answers becomes a named failure, never a permanent pending clause.

That named failure is RETRYABLE. It answers rechecks for kMountEligibilityReadRetryBackoff (doubled per consecutive failure of the same bead), and the first evaluation after that reads again — so a bead whose read lost a boot burst recovers on its own, and no bead ever needs an edit to its content to be looked at a second time.

The fresh read is a FilingService.inspect rather than a bare bead query, because a receipt bound to a filing basis can only be judged against a re-evaluation of that basis — the bead's own fields plus the dependency ROWS the substation store holds. A bound receipt therefore refuses SYNCHRONOUSLY as unevaluated (there is no revision to compare yet) and mounts only once the recomputed revision matches the stamped one. The legacy raw-sha receipt has no basis to re-derive, so a complete one still passes through synchronously and queries nothing.