Round-3 review of the S3 config-fold, all in routes/scheduler.py:
- stale docstring: "Persisted to app_state" -> "Persisted via sysconfig" (the
batch moved stores in B-core-11; the comment didn't follow).
- drop the manual min/max check in the PATCH — sysconfig.set_value already
validates against the same spec bounds; catch its ValueError -> 400, matching
the config PATCH pattern (bounds enforced in one place).
- fetch sysconfig.spec(...) once into a local in the GET instead of twice.
No behaviour change beyond the 400 message wording (untested path). 368 pass.