5.130.0: the 50% overnight minimum holds when Flux cannot plan

[Highsteads]

Not deployed. This is for review before anything is installed or released.

What went wrong on 1 October

• Octopus published October's Flux import prices (13.92p cheap, 23.19p day, 32.48p peak) but no export price after midnight, in any region. The account is still on E-1R-FLUX-EXPORT-23-02-14-F, open-ended.
• With no export price, derive_bands refused (correctly: it must not invent a price), so Flux deferred from 00:00 onwards. It was still deferring at 13:40, so there is no Flux peak sale today either.
• The ordinary manager bought to its own household target of 44%, went back to self consumption at 03:48 and ran the house on the battery. The battery was at about 42% at 5am against the agreed 50%.
• The 50% rule lived only inside the Flux planner, so it lapsed with it.

What changes

• One rule, two users: flux_strategy.cheap_window_minimum_pct() gives 50% in 02:00-05:00, or nothing on a day with a booked free hour. Flux and the manager both read it.
• Manager fallback: while Flux is not running the window, the manager charges to the highest of the 50% minimum, tomorrow's need and the reserve, then holds until 05:00 with the house on the cheap grid. It never buys for the peak.
• Handing back to Flux: once the manager's charge is only holding, Flux can plan and take the window back.
• Late-window sizing: the minimum is now sized on the real time left; it used at least 15 minutes. Shortfalls are reported.
• 5am report: at 5am the Event Log says the battery level actually reached against the minimum. It is a warning if below 50%. Each night is also written to cheap_window_results.jsonl.
• Clearer message: "no Flux decision" now names the missing side and the time, for example "Octopus has not published the Flux export prices beyond 00:00 on 1 October".

Checks

• 36 new tests, built on the real published spans from 30 September and 1 October.
• Eleven mutations, all caught.
• Full suite 2,367, lint clean.
• All 29 simulator scenarios are unchanged.

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