fix(octopus): count the Intelligent daily cap in dispatch minutes, not half-hour blocks

[springfall2008]

This is an automated draft PR generated from issue #5510 — a maintainer should review it before merging.

Fixes #5510

Summary

The Octopus Intelligent daily cap (octopus_slot_max, 6 hours on IOG-SMB) was counted in 30-minute blocks rounded outwards, so a 10-minute dispatch used 30 minutes of it, and the two counters disagreed with each other. Both now count the dispatch's own minutes:

• Completed dispatches: the start and end Octopus sends, taken as correct.
• Planned dispatches: the exact planned start and end.
• Real charging time inside a dispatch is not worked out; that is left to Octopus.

rate_add_io_slots() (rates) and load_octopus_slots() (car plan) now charge the budget through one shared helper, take_cap_minutes(). octopus_slot_max is still set in 30-minute slots in apps.yaml and multiplied out internally, so existing configs are unchanged.

Behaviour changes to check

• The half hour the budget runs out in stays cheap for the house. The rates are still stamped by whole plan periods: a period with any dispatch minute inside the budget is cheap throughout. The car plan splits at the exact minute. This was the open point in the issue; say if the rates should cut off at the exact minute instead.
• rate_add_io_slots() now takes dispatches earliest first, as load_octopus_slots() already did, so the budget goes to the same dispatches in both. It used to take them in the order given.
• The debug log line is now Octopus: Intelligent slot minutes for day N: X of Y max, in minutes.
• Capped installs will see more dispatches priced off-peak than before whenever their dispatches do not line up with half hours. Uncapped tariffs (48 slots) are effectively unaffected.

Testing

• New cases in test_rate_add_io_slots.py (run_cap_minutes_tests), each run through both counters: a short completed dispatch, two dispatches in one half hour, overlapping completed and planned dispatches, and a dispatch that crosses the end of the budget.
• Fails without the fix, passes with it: with octopus.py reverted, rate_add_io_slots fails on all four new cases (rates and car plan); with the fix, rate_add_io_slots and octopus_slots both pass.
• Existing expectations in test_octopus_slots.py that encoded block counting were updated: eight 60-minute dispatches from 14:05 used to hit the cap after four (three blocks each) and now hit it after six.
• unit_test.py --quick: all tests passed (4 slow tests skipped).
• pre-commit passes on the five changed files.

Notes

• Remaining ways the two counters can differ, all there before this change and left alone:
  • load_octopus_slots() clamps dispatches to today, so it does not see the part of the current midday-to-midday period that fell before midnight; rate_add_io_slots() does.
  • With octopus_slot_low_rate: false the car plan counter does not run at all.
  • Minutes withheld on the rates side (car seen not charging, or no car needs them) use no budget there, and the car plan has no equivalent.
• The cap is still per car (octopus_slot_max is derived per account but enforced per car #5215), the period is still midday to midday keyed on the dispatch's start, and a past dispatch with zero kWh still uses no budget.
• Whether Octopus really measures the cap in minutes cannot be checked from the repo; this follows the maintainer's direction on the issue.
• GitNexus impact reports no callers for either function, because they are reached through the PredBat mixin. By search the callers are fetch.py (both) and output.py (load_octopus_slots()); detect_changes rates the change medium.

🤖 Generated with Claude Code

[Copilot]

🟡 Changes recommended

Active zero-kWh dispatches still consume different cap durations in the rate and car-plan counters.

1 open finding

• Cap accounting undercounts active zero-kWh dispatch duration · New

What changed in this PR

Fixes #5510 by accounting for Octopus Intelligent caps in dispatch minutes rather than rounded half-hour blocks.

Changes:

• Adds shared minute-based cap accounting.
• Aligns rate and car-plan behavior and updates tests.
• Clarifies configuration documentation.

File	Description
apps/​predbat/​octopus.py	Implements minute-based cap accounting.
apps/​predbat/​tests/​test_rate_add_io_slots.py	Adds cap regression cases.
apps/​predbat/​tests/​test_octopus_slots.py	Updates car-plan expectations.
docs/​car-charging.md	Documents minute-based accounting.
docs/​apps-yaml.md	Clarifies configuration units.

🧠 Review effort: Balanced

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