Precedence arbiter: one rule instead of an if/else ladder

Two controllers writing one actuator is the failure this system exists to
avoid. "Exactly one writer" was true, but only as a convention held up by
careful reading - which does not survive an EV charger and a heat pump wanting
the same battery.

Strategies now return claims and arbiter.py resolves them:

  highest-priority `set` wins (none at all means 0 W), then every `limit` whose
  priority is >= that set's applies, most restrictive first; contradictory
  limits command 0 W and are flagged as the bug they are.

The second clause is the whole point. "Money outranks maintenance" used to be a
hand-written exception inside a Jinja template; it is now a consequence of the
priorities - the charge-only limit binds the loop but cannot bind a
higher-priority peak claim.

Also: maintenance shaping moved out of control.py, which is a controller again
and not a policy engine; the loop now tracks the arbiter's actual output rather
than its own last wish, so it does not jump when it regains control; and every
decision explains itself ("loop -> 0 W, limited by maintenance(charge-only)")
in the UI and the log.

19 new assertions in test_arbiter.py, each one a precedence question someone
will eventually ask in the field. Deployed to the reference site as 0.2.0 and
holding grid within a few watts of zero.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016NckgXecasQb2eSsPYNSW6

goodwe_controller/app/control.py

@@ -44,9 +44,6 @@ def compute(
     actual_w: float,
     tuning: Tuning,
     sat_count: int = 0,
-    *,
-    charge_only: bool = False,
-    charge_floor_w: float = 0.0,
 ) -> Decision:
     """One control cycle. A cycle is one meter update (~5 s on a HomeWizard P1).
 
@@ -83,15 +80,10 @@ def compute(
     else:
         want = prev_w + tuning.gain * grid_w
 
-    # --- maintenance charge shaping ---------------------------------------
-    # Applied BEFORE clamp and slew so a forced charge is still rate-limited
-    # like any other demand.
-    if charge_only:
-        want = min(want, 0.0)
-        reason = "charge-only"
-        if charge_floor_w > 0:
-            want = min(want, -charge_floor_w)
-            reason = "charge-floor"
+    # ⚠️ Maintenance shaping (charge-only, cheap-window floor) used to live
+    # here. It now belongs to arbiter.py as limit claims, so that precedence
+    # between strategies is decided in ONE place. This function is again what it
+    # should be: a controller that knows only about tracking the meter.
 
     # --- ORDER MATTERS: clamp -> slew -> freeze ----------------------------
     # An early draft applied a floor after the clamp and let demand escape it.