increment_probe_failures / reset_probe_failures did a non-atomic
get_state (GET) -> mutate -> set (SET) in Python. A concurrent
activate() re-park writes a FRESH episode blob (probe_failures: 0 +
fresh activated_at / retry_after / affected_agents / kind); if the
stale increment's SET landed after the fresh activate's SET, the stale
blob overwrote the fresh episode metadata AND un-reset the counter
(clobbering the new episode).
Redis single-threads a Lua EVAL, so a server-side read-modify-write
is indivisible: activate's SET is serialized entirely before or after
the script, never interleaved between the script's GET and SET. The
two scripts mutate ONLY probe_failures, so every other episode field
survives the bump. activate stays a single atomic SET (a fresh episode
resetting the counter to 0 is correct semantics).
