TEL-01: P1 ingestion, with the derivation and the age the EMS owns

A Belgian P1 meter publishes two UNSIGNED registers, not one signed figure.
Until now the add-on asked the installer to bridge that gap with a template
sensor, which put the sign convention of the whole control loop in a text box.
This moves it into the EMS: net = import - export, derived once, in one place,
with a test that fails if anyone inverts it.

Two transports behind one contract, chosen by `meter_source`: the HA WebSocket
subscribing to the DSMR integration's entities, and MQTT on a configurable
topic. Everything downstream reads P1Ingest, so switching is a config edit.
`meter_source: off` is the default and keeps the existing meter_entity path,
so no installed system changes until it opts in.

The other half is the timestamp. Every accepted sample is stamped at ingest
with a monotonic clock, `meter_max_age_s` is applied to it, and the age is
published as sensor.p1_sample_age_s for the ESP32's stale-input watchdog. That
entity is recomputed against the clock every second rather than only when a
telegram lands, because HA pushes state only on change: a meter frozen at a
constant reading emits nothing and looks, to anything watching the value,
exactly like a meter that has died. The age tells them apart.

Deliberately absent: any fallback to an inverter-side power figure. The
inverter's own AC power correlates 0.998 with battery power and 0.09 with the
real meter, so failing over to it means regulating against your own output.
A gap stays a gap - a reconnect emits no synthetic sample, and a rejected
telegram never resolves to 0 W or refreshes the timestamp.

Quarter-hour averages are time-weighted over clock-aligned blocks rather than
a mean of samples, so a cadence change cannot bias the capacity-tariff figure,
and only offtake is accumulated so a quarter of pure export averages to 0 kW.
Per-phase import is kept separately: on an unbalanced three-phase load the
phase sum and the connection net are different numbers, and only one of them
is billed.

test_p1.py: 99 checks, runnable with a bare interpreter and no meter. Includes
an end-to-end run of the HA transport against a fake Home Assistant websocket.

Stacked on SAFETY-04; nothing here touches control.py.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Du77usMj8XNKNFZGmUiWDa

goodwe_controller/config.yaml

@@ -39,6 +39,23 @@ options:
   batt_invert: false
   setpoint_entity: ""
 
+  # --- P1 meter ingestion (specs §5.2 / §14 `meter:`) -------------------------
+  # `off` keeps the original single meter_entity path above, so an existing
+  # install is untouched until it opts in. ha_dsmr subscribes to the DSMR
+  # integration's entities over the HA WebSocket; mqtt_p1 reads the topic below.
+  meter_source: "off"
+  meter_phases: 1
+  meter_max_age_s: 30
+  meter_mqtt_topic: ""
+  # The two UNSIGNED Belgian registers. The EMS derives net power from them
+  # (import - export); do NOT point these at a signed template sensor.
+  p1_import_entity: ""
+  p1_export_entity: ""
+  # Optional, in L1..L3 order. Required for the capacity-tariff peak on a
+  # three-phase connection; the list length must equal meter_phases.
+  p1_phase_import_entities: []
+  p1_phase_export_entities: []
+
   # --- control ---------------------------------------------------------------
   max_w: 2000
   gain: 0.6
@@ -81,6 +98,21 @@ schema:
   batt_invert: bool
   setpoint_entity: str
 
+  meter_source: list(off|ha_dsmr|mqtt_p1)
+  # ⚠️ 2 is accepted by this range but is not a real Belgian connection. A
+  # telegram whose phase count disagrees is rejected at ingest and logged, so a
+  # mis-set 2 shows up immediately as "0 telegrams accepted" rather than as a
+  # quietly wrong number.
+  meter_phases: int(1,3)
+  meter_max_age_s: int(5,300)
+  meter_mqtt_topic: str?
+  p1_import_entity: str?
+  p1_export_entity: str?
+  p1_phase_import_entities:
+    - str
+  p1_phase_export_entities:
+    - str
+
   max_w: int(100,5000)
   gain: float(0.05,1.0)
   slew_w: int(50,5000)