Site: don't apply battery priority to loadpoints with battery boost active

[webalexeu]

Fixes #30541

Desired behavior

Battery boost deliberately drains the home battery into the vehicle and has its own soc floor via batteryBoostLimit (boost auto-disables when the battery soc drops below it). Therefore battery priority (prioritySoc) does not apply to a loadpoint with boost active: it may claim the power currently charging the battery. All other loadpoints keep respecting battery priority unchanged.

Problem

Below prioritySoc, sitePower() hides the power flowing into the battery (batteryPower, excessDCPower zeroed) and forces a 100W residual so loadpoints leave the surplus to the battery. This also starved boost-active loadpoints: with the battery charging at 2000W, the boosting loadpoint ramped at ~0.4A per cycle instead of ~9A and could stay stuck on 1 phase (see issue for the full calculation).

Solution (contained, per #30541 (comment))

• sitePower() additionally returns the priority adjustment it applied (zeroed batteryPower + excessDCPower plus the residual override delta). Adding it back exactly reconstructs the unadjusted site power; the excessDCPower term self-corrects, so DC-only excess that no loadpoint can claim stays reserved for the battery.
• site.update adds the adjustment back only for the loadpoint being updated when its boost is active. Loadpoints are updated one per cycle, so there is no double-counting with multiple boost loadpoints.

Covered by the new table-driven TestSitePowerPriorityAdjustment (charging above/below prioritySoc, discharging below), exercising the full sitePower path with mocked battery meters.

Known edge case: on the cycle where boost auto-disables (soc fell below batteryBoostLimit), the loadpoint may see one interval of unadjusted surplus before reverting — keeping the boost check out of sitePower is what keeps the change contained.

🤖 Generated with Claude Code

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[mfuchs1984]

This looks nearly identical to my prototype, see master...mfuchs1984:evcc:fix/boost_below_prioritysoc

The only difference is that your add excessDCPower to priorityAdjustment, while my attempt reduces priorityAdjustment by excessDCPower. Don't know which one is right, should IMHO be understood before merging, and covered by a test.

[webalexeu]

This looks nearly identical to my prototype, see master...mfuchs1984:evcc:fix/boost_below_prioritysoc

The only difference is that your add excessDCPower to priorityAdjustment, while my attempt reduces priorityAdjustment by excessDCPower. Don't know which one is right, should IMHO be understood before merging, and covered by a test.

Indeed, I've added a test yo cover it

@andig Can you have a look to see what you think ?