FABRIC.md: note-to-self on the fleet heat truncation leak before 5.1

Punch list §25.7 addition, not a punch list item.

Captain Bob flagged the existing "fleet heat leaks on every multi-VM
touch" entry (§20.2/§25.7) as worth a pinned reminder: it's currently
invisible because Tripod is pruned to Hera alone (item 0.1), so
others_total is always 0 and the leaky division path never executes.
It becomes reachable, and measurable, only once Phase 4 restores
Hermes/Artemis -- so a clean item-5.1 DoE re-run before that point
would be a false negative on VM-CONSERVED?, not evidence the
conservation law holds. Still reported-not-scheduled on purpose.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

FABRIC.md

@@ -2726,6 +2726,15 @@ so.*
   fleet heat drifts downward monotonically. `VM_PHYSICS_EPSILON_Q48` is 5% of `Q48_ONE`, so
   a long enough run would trip `VM-CONSERVED?`. Nobody has measured the rate. This is a
   live defect in a conservation law the project makes claims about — see §20.2.
+
+  > **Note to self, flagged by Captain Bob 2026-08-04, before item 5.1.** Currently
+  > invisible: with Tripod pruned to Hera alone (item 0.1), `others_total` is always 0, so
+  > this path is never exercised — nothing today can trip it. It becomes reachable, and
+  > therefore measurable, the moment Phase 4 restores Hermes/Artemis. Check this before
+  > trusting item 5.1's DoE re-run as evidence that `VM-CONSERVED?` holds: a clean run on a
+  > document this careful about falsifiability elsewhere, sitting on top of an unmeasured,
+  > monotonic leak, would be a false negative, not a green light. Still reported-not-
+  > scheduled on purpose — becomes its own item only if Captain Bob says so.
 - `hotwords_cache_promote()` writes NULL into the ring if `word` is NULL and the cache is
   full (`physics_hotwords_cache.c:363-364`). Unreachable today.
 - `heartbeat_trust()` is exported and has zero callers.