fix(sunsynk): make the settings write actually work — group, Sell flag, encodings

[springfall2008]

First live write test against a real Sunsynk inverter. Control could never have worked before this — three separate defects each independently blocked it, and every one is invisible from the API's responses, which report {"code":0,"msg":"Success","success":true} for writes it silently discards.

The inverter was returned to its original settings after every probe, verified each time.

1. The endpoint discards an oversized object

Posting all 350 settings keys returned success and changed nothing — confirmed twice, including a probe that altered a single field and preserved every original string type. Posting only the System Mode group made the identical change persist immediately.

The whole-object read-modify-write the design was built on is simply wrong for this API. Predbat now sends that group only, which is also safer: battery, grid and generator settings are never transmitted by a schedule write, so a schedule write cannot disturb them.

2. The per-slot Sell flag was missing entirely

sellTime{n}En is the third per-slot flag in the app, alongside Grid Charge and Gen Charge. It must be 1 for a forced export slot, so export windows could never have armed.

Worse, its absence from the payload also made the API silently drop time{n}on. Grid charge failed to write on six consecutive attempts — bare True/False, "true"/"false", "1", 1, "True", "on" — while the rest of each write persisted every time. The API validates the per-slot field set as a whole and drops the flags if it is incomplete.

With all the flags present they are independent, proven in a single write by setting grid charge on a slot whose Sell flag is 0, and the Sell flag on a slot whose grid charge is 0:

slot2  gridChg=true  En=0  ->  both landed exactly as sent
slot4  gridChg=false En=1  ->  both landed exactly as sent

3. Boolean encoding

Booleans must be the strings "true"/"false", not bare JSON booleans — the opposite of what solarsynkv3's ReplaceTRUE() helper implied, which was the original basis for the guess. sellTime{n}En is the exception: it takes the numeric "1"/"0" the API returns for it.

saturdayOn flipping correctly in the same write that dropped time2on is what proved string booleans work in general and isolated the problem to the per-slot set.

Also: a server-derived field

time{n}On (capital O) must never be written. It changed from '0' to '65' on a write that never mentioned it, and writing '1' produced '65' too. It is not the boolean it resembles; the writable grid-charge flag is time{n}on, lower case.

Verification

A combined charge and export plan, written through the real component:

 slot  start   cap   gridChg  sell   power
  1    00:00    20%   false    0     8000
  2    02:00    90%   true     0     3000   <- charge window
  3    04:00    20%   false    0     8000
  4    05:00    20%   false    0     8000
  5    16:00    30%   false    1     2500   <- export window
  6    19:00    20%   false    0     8000

• 33/33 owned fields written and read back exactly
• 0 of the 350 settings keys lost
• nothing outside the System Mode group changed
• inverter restored to its original settings, 33/33

All 7 Sunsynk suites and the full --quick run pass. New tests pin the group restriction, the Sell flag's presence on every slot and its value on export slots, the quoted-boolean encoding, and that the server-derived field is never transmitted.

Note for the DEYE component

Neither solarsynkv3 nor synkctl writes sellTime{n}En — both use the lower-case time{n}on alone, so both likely have the same silently-failing write. deye.py models its slots on the same registers and may share the gap; worth checking whether TimeUseSettingItem has an equivalent enable that Predbat is not setting.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes Sunsynk schedule/control writes by aligning Predbat’s settings payload with the Sunsynk Cloud API’s real constraints (writeable field group restriction, required per-slot Sell flag, and string-boolean encoding), so that inverter settings changes actually persist.

Changes:

• Restrict settings writes to the “System Mode” settings group only, avoiding full-settings read/modify/write that the endpoint silently discards.
• Add and populate the per-slot Sell enable flag (sellTime{n}En) and ensure per-slot flag sets are complete so writes aren’t dropped.
• Update boolean encoding to the API-required "true"/"false" strings and add tests that pin the new behavior (including never writing server-derived time{n}On).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
apps/predbat/sunsynk.py	Builds payloads from System Mode baseline only; adds per-slot Sell flag handling; avoids leaking server-derived slot fields.
apps/predbat/sunsynk_const.py	Adds System Mode field allowlist, derived-field denylist, Sell flag template, and updates boolean encoding behavior.
apps/predbat/tests/test_sunsynk_control.py	Expands control/payload tests to enforce group restriction, Sell flag presence/value, string-boolean encoding, and derived-field exclusion.
apps/predbat/tests/test_sunsynk_const.py	Updates encoding expectations to match quoted boolean behavior.

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