[codex] Fix cumulative EVCC energy export

[fbettag]

Summary

• Parse EVCC chargeTotalImport from /api/state.
• Prefer chargeTotalImport for Victron /Ac/Energy/Forward so continuous/heating devices with chargedEnergy == 0 still publish a cumulative kWh counter to VRM.
• Keep chargedEnergy / 1000 as fallback for older/missing EVCC payloads.

Root Cause

On a live heat-pump loadpoint, EVCC reports a valid cumulative import meter but keeps the session energy at zero:

chargePower       ~= 27-90 W
chargedEnergy     = 0
chargeTotalImport ~= 19342 kWh

The bridge previously exported /Ac/Energy/Forward from chargedEnergy / 1000, so VRM received 0 kWh even though the loadpoint had a valid cumulative meter value.

The EVCC setup uses a sgready-relay charger with a separate Shelly 3EM meter. EVCC logs confirm that loadpoint 3 has charge total import values, so the bridge can forward that cumulative meter directly.

Validation

178 passed in 0.22s

Run with:

nix-shell -p python3 python3Packages.pytest python3Packages.requests python3Packages.requests-mock shellcheck --run 'python3 -m pytest -q'

[okuegow]

Thanks — clean fix, the logic is right. Two small things before merging:

Unit is kWh, confirmed. Cross-checked on a live /api/state: with an EV loadpoint showing a recent session of ~35 kWh while chargeTotalImport was ~15.3k, only kWh is consistent (lifetime can't be smaller than a single session). IntegratedDevice chargers (sgready-relay, heatpump, sgready, mypv, vaillant) explicitly have no session semantics in EVCC, so chargedEnergy is structurally unsuitable for those — chargeTotalImport is the right field.

Source switch breaks monotonicity. Victron's /Ac/Energy/Forward is expected monotonic, but the current branching switches source dynamically. On a loadpoint where EVCC returns chargeTotalImport: null (e.g. no meter on the charger), the fallback flips to chargedEnergy/1000 — which is 0 on a heating LP, rolling the counter back. Minimal guard, no new state:

total_import = float(lp.charge_total_import or 0.0)
if total_import > 0:
    candidate = total_import
elif status != STATUS_DISCONNECTED:
    candidate = float(lp.charged_energy) / 1000.0
else:
    candidate = None

if candidate is not None:
    previous = float(s.get("/Ac/Energy/Forward") or 0.0)
    s["/Ac/Energy/Forward"] = max(candidate, previous)

Plus a test that flips the source mid-run (high → 0 → high, no regression).

Side note worth a line in the description: /Ac/Energy/Forward is now written even when DISCONNECTED (whenever total_import > 0). That's the right semantics for a lifetime counter but is a deliberate change from the original "keep last value on disconnect" — a test for the disconnected+positive case would make it explicit.

Happy to push a follow-up commit if easier.