MAINT-13 round 3: provider site, hourly fixed-tariff check, faster tests

- A price-provider site with no fixed tariff is not a gate (its plan never
  sets `cheap`); DECISIONS §3 says so and a test pins it.
- The fixed-tariff check is worked out once an hour, not every tick.
- test_maint13: run() steps really are `step` minutes; the long loops use
  5-minute steps (the per-tick cap); wall backstop checked "not before".
- test_safety93: the drain bound is the rig's configured drain rate.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

goodwe_controller/DECISIONS/MAINT-13-full-pack-is-complete.md

@@ -67,7 +67,13 @@ holds the charge back, and `cheap` is always false there), in a cheap window, or
 while the pack is really taking charge (battery power at or below -50 W, which is
 sun outside cheap hours). It is false only when a gate exists, is shut, and the
 pack is not charging; a pack asked for charge that delivers nothing then does not
-count, which is the case the clock cannot judge. Only open ticks add to `open_min`; one tick
+count, which is the case the clock cannot judge. A site with a price provider
+(TARIFF-11) and no fixed tariff counts as having no gate: the provider's plan
+reaches only the Tariff row, never `cheap`, so no cheap window ever opens a grid
+top-up there and only the sun charges the pack, as on a site with no tariff. Its
+time counts in full. When a provider plan starts to drive `cheap`,
+`_price_gated` must become true for it. Whether a fixed tariff is set up is
+worked out once an hour, not on every tick. Only open ticks add to `open_min`; one tick
 adds at most 5 min, so a gap (add-on down) adds nothing. The stall wait pauses
 while the gate is closed. The accounting is written to the state file at most
 every 5 min (`charge_track`); a restart loses at most that. A state file from