Release 0.21.0: CHANGELOG wording (SAFETY-136, SAFETY-138 known issues)

SAFETY-136: the line said 10 to 15 s late is not caught, then that 15 s late
is caught after about 4 minutes. It now says 10 s is not caught and 15 s only
after about 4 minutes, as the card says.
SAFETY-138: the 30 s timer that zeroes a late write is the ESPHome board's
watchdog (README), not the inverter's own.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

goodwe_controller/CHANGELOG.md

@@ -1,12 +1,123 @@
 # Changelog
 
-### Not in a release yet
+## 0.21.0
+
+**A minor bump: control now holds the batteries when Home Assistant readings come late, Home draws the whole night's grid charge, and the shutdown 0 W is sent last. No option changes.**
+No option was added, removed or renamed, and no default changed (86 options). **Existing installs need no option change:** options that start 0.20.1 also start 0.21.0, and the Supervisor form is the same. It is a minor bump because control acts differently when readings come late and when the add-on stops; every saved setting still starts.
+
+**Late Home Assistant readings are held, not followed.** When Home Assistant passes readings on late, control used to correct a mistake its last command had already fixed, so the give run could swing and send power to the grid. It now waits until the battery shows its last power request, and the peak limit no longer asks for full power on late readings. A row on the page says so, and if the readings stay too late every inverter goes to 0 W. With readings on time, the commands are the same as before.
+- With a 2 s meter, readings 10 s late were found in 43 s in a rig test.
+- With a 5 s meter, readings 30 s late are now found in about 90 s (88 s in a simulation, 75 s in a rig test), where they took about 3 minutes. Readings 10 s late at a 5 s meter are not found ([[SAFETY-136]]).
+
+**Home draws the whole night's grid charge.** Home used to draw a battery's grid charge only for the cheap run under way. It now draws every hour the add-on will charge it tonight, and shares the peak room between batteries as control does. It shows the plan and changes no command.
+
+**Tomorrow's forecast stays in the afternoon.** If one of the tomorrow solar forecast sensors stops updating, tomorrow's forecast now stays instead of vanishing until 20:00.
+
+**The shutdown 0 W is sent last.** When the add-on stops, the 0 W now waits up to 2 s for a command already on its way, so it is the last thing each inverter hears. A command slower than that can still land after it ([[SAFETY-138]]).
+
+Contents of this release, in merge order since 0.20.1 (`d53f70f`):
+
+| | |
+|---|---|
+| `371961e` | When Home Assistant passes readings on late, control no longer corrects a mistake its last command has already fixed. It waits until the battery shows its last power request, and the peak limit no longer asks for full power on late readings. The page says so, and if the readings stay too late every inverter goes to 0 W ([[SAFETY-128]], #228) |
+| `af2d0d2` | History only: brings 0.20.1, already live, into this branch. Nothing else is new (#233) |
+| `47c89a1`, `c66aa7f` | Home draws a battery's grid charge for every hour the add-on will charge it tonight, not only the cheap run under way, and shares the peak room between batteries as control does. It shows the plan and changes no command ([[UX-77]], #234, with its second round #235) |
+| `b291262` | With a 5 s meter, readings 30 s late are found in about 90 s, not about 3 minutes. Readings 10 s late are not found at a 5 s meter; the owner accepted this and it has its own card ([[SAFETY-129]], #236, [[SAFETY-136]]) |
+| `23ff9d0` | If one of the tomorrow solar forecast sensors stops updating in the afternoon, tomorrow's forecast now stays on the Forecast tab instead of vanishing until 20:00. The night plan can use it in that time ([[OPT-38]], #237) |
+| `57c8d1b` | Each inverter is now reached through a driver. This prepares support for other inverter makes; there is no change for GoodWe sites ([[SMA-2]], #238) |
+| `dbdc37b` | When the add-on stops, an inverter that can steer itself can be handed back instead of held at 0 W. This prepares support for other inverter makes; there is no change for GoodWe sites ([[SMA-10]], #239) |
+| `b3cfcf2` | When the add-on stops, the 0 W now waits up to 2 s for a command already on its way, so it is the last thing each inverter hears. In a rig test, 0 of 111 stops ended on a value other than 0 W, against 4 of 110 before. A slower command can still land after it ([[SAFETY-137]], #240, [[SAFETY-138]]) |
+
+### Known issues
+
+- A false "Battery is not keeping up" can still show when the peak guard pauses a maintenance charge ([[SAFETY-92]]).
+- A battery capped at a low limit with a perfectly flat reading can still trip the stale check ([[SAFETY-74]]).
+- A battery whose reading at rest is beyond about ±175 W is still not caught when it refuses ([[SAFETY-97]]).
+- The peak guard can still back off near the end of a 15-minute period when a meter reading is late, by less than 30 s. This is about the guard's discharge only; a grid charge is cut back since 0.19.2 ([[SAFETY-99]]).
+- Two inverters: the maintenance charge can switch on and off while the house is above the peak aim ([[SAFETY-88]]).
+- Two inverters: the "circulating" figure counts a battery's reading at rest ([[SAFETY-98]]).
+- Two inverters: a drain that starts during a big step in house use can send the other battery to full power, and about 1 kW goes to the grid for about 10 s ([[SAFETY-104]]).
+- Two inverters: when a battery comes back during a maintenance charge, the grid can step by several kW at once ([[SAFETY-101]]).
+- Two inverters: when a battery drops out during a solar surplus, the others can swing by up to 1.5 kW in a simulation ([[SAFETY-105]]).
+- Two inverters: after a drain ends, a change in house use can go unanswered for about 9 s, because some readings are old ([[SAFETY-106]]).
+- Two inverters: when one battery's level is missing, both batteries are held at 0 W, and for about 15 s the last command stays on ([[SAFETY-108]]).
+- Two inverters: if one battery's level stays missing for 12 h, the other battery's cycle can be marked failed, with a 7-day wait and a notice, though it is healthy. This comes from reading the code; it has not been seen on a site ([[MAINT-17]]).
+- When the 15-minute demand forecast sensor counts the battery's own charge, the maintenance charge runs at about half the power the peak limit leaves, so it takes about twice as long. Seen on a site: about 1.2 kW instead of 2.5 kW, and the peak limit was kept ([[SAFETY-111]]).
+- One inverter: after a link drop, the battery's own safety stop to 0 W can be taken as a refusal, and the site stays at 0 W for up to 15 min ([[SAFETY-102]]).
+- After a Home Assistant restart, control still waits until Home Assistant has finished starting, which can take several minutes, though the readings are already there ([[SAFETY-115]]).
+- While Home Assistant is not answering, the page can list inverters as refusing commands and sensors as missing, and send you to Developer Tools, though they are fine ([[UX-37]]).
+- If Home Assistant hangs or stops, the page keeps saying "Waiting for Home Assistant" and never turns into an alarm ([[SAFETY-113]]).
+- Right after Home Assistant has started, the page can say for about 4 s that an inverter cannot be controlled, and the first command can come late ([[SAFETY-114]]).
+- After a Home Assistant restart, the controller status sensor can still say "running" while the add-on cannot control. It was seen once, and the cause is not known ([[SAFETY-116]]).
+- Battery modes on: after a planned top-up from the grid, the Batteries screen can say "Enough sun is forecast" ([[UX-32]]).
+- Battery modes on: the forecast line "we count on" can show more sun than the plan counts, because the plan takes house use off first ([[UX-33]]).
+- Battery modes on: before a planned top-up, the Today list shows a smaller "gives" amount than the plan will use; it grows as the charge happens ([[UX-34]]).
+- Two inverters, battery modes on: while the other battery is in its maintenance charge, a battery's card can say it charges from the grid while it stays at 0 W ([[OPT-18]]).
+- Two inverters, battery modes on: while a battery refuses to charge in a cheap run, the action log on the page gets about 8 lines an hour for its retries, and the page hint says "waiting for a better price" ([[UX-38]]).
+- A battery in a safety stop, or one the add-on cannot reach, can still be started for a cycle, and its drain then waits about 12 h and ends in a failed-cycle notice. This comes from reading the code; it has not been seen on a site ([[MAINT-19]]).
+- On the Settings page, the rows of the solar forecast lists are labelled "Phase 1", "Phase 2" instead of "Sensor 1", "Sensor 2" ([[UX-27]]).
+- In the solar forecast list, a blank or repeated row makes "source 2 of 2" count differently from the rows on the Settings page ([[UX-28]]).
+- The solar forecast message says "has no reading" also when the sensor shows a number that is too old or in the wrong unit ([[UX-29]]).
+- If you use only the forecast lists, two Settings notes sit on the single-sensor field, and one of them tells you to set that field ([[UX-30]]).
+- After a restart during a price outage, the "No prices" message can say "yet" when prices did come in earlier ([[UX-39]]).
+- On the new settings page, you cannot see whether a price service token is set. Check the Configuration tab ([[UX-41]]).
+- On the classic settings page, the first click on Save after editing a field can do nothing. Click again ([[UX-42]]).
+- A steady overload on a 1 s meter can warn, and send the Home Assistant notification, 2 or 3 times at the start of each 15-minute period instead of once. The peak limit is still kept ([[SAFETY-122]]).
+- A fixed tariff is priced once per hour, so a price window that starts or ends at :15, :30 or :45 gets the wrong price for part of that hour. Windows that start and end on the hour are right ([[TARIFF-23]]).
+- Step 6 of the setup wizard stays empty because of an error in the page, in English and in Dutch ([[UX-51]]).
+- On Dutch pages, refusal texts, the last-event line under the Home buttons, the installer details and the trading status sentences are still English, and a few Dutch texts read badly, such as "1 metingen geweigerd" ([[UX-52]]).
+- Some price texts say "hour" where the add-on acts on a 15-minute period, such as "cheapest hour" ([[UX-47]]).
+- After the add-on restarts, the Home price chart shows no price for the earlier part of today, and the setup check can say "12 of 24 hours", though the prices are known ([[UX-48]]).
+- With battery modes on and only batteries on "Leftover solar", the Home price chart can mark a cheap period where no battery charges ([[UX-49]]).
+- On a phone, the bars of the Home price chart are too thin to tap one 15-minute period. The arrow keys work ([[UX-50]]).
+- In the last second of a 15-minute period, being a few watts over the aim can make the peak guard ask a battery for full power for one second. When a charge ends on a period edge, the last-second give can fade out over about 10 s, and a rig test exported up to 7.4 kW for about 8 s ([[SAFETY-124]]).
+- During the night grid charge, a 15-minute period can end 6 to 14 W over the peak aim, because the battery charges harder than asked. This was seen in simulation; a rig test saw 2 to 8 W ([[OPT-35]]).
+- The test rig could not bring back the false peak alarm that [[SAFETY-126]] fixes, so that fix is shown in simulation only. Watch the notifications for a few nights ([[TEST-35]]).
+- The night cheap run is sized for the batteries' full charging power, not for what the peak limit leaves. Under a tight limit the run can end before the batteries reach their level, and Home can show a level they do not reach (79.9 % against a shown 95 % in a rig test) ([[OPT-25]]).
+- By day, a Leftover solar plan that has only a daily forecast figure counts the sun from now, not from when the figure was read. It counts about 22 % too much for a figure one hour old; the night plan is not affected ([[OPT-30]]).
+- The night charge can buy too much in a house that uses more at night than by day, such as one with a car charger or heat pump, and on a sunny day, because spare sun in one expensive hour does not count for the later ones ([[OPT-31]]).
+- A cheap run that has already started can overlap a new give run after a re-plan, so a battery can charge from the grid at the dearest price for part of an hour. This was seen in a test case, not on a site. Also in 0.19.2 ([[OPT-32]]).
+- If the solar forecast sensors stop updating before 17:00, as in winter or further north, there is no forecast from three hours after their last update until 20:00 ([[OPT-33]]).
+- With a forecast that gives only a daily total, the sun is spread an hour off on the two clock-change days after the change. The day's total is right ([[OPT-24]]).
+- The add-on learns the house's use only once a solar forecast is set, so a site that adds a forecast later waits one more day for its first plan ([[OPT-26]]).
+- Home says "No trading on price yet: no prices have arrived" when every battery is on Solar first, though the prices are shown ([[UX-55]]).
+- The Home plan header can say "Charges in the cheapest hour, gives power in the dearest" when Home draws no charge, and it says "hour" for 15-minute prices ([[UX-56]]).
+- While the peak guard holds back charging, Home hides the rest of the cheap run and gives no reason. The charge starts again when the guard lets go ([[UX-57]]).
+- With battery modes on and selling on, Home can draw a "Sells up to" block when the add-on judges the trade not worth it, and then it will not sell ([[UX-58]]).
+- Home, the plan and the Forecast tab stop drawing a battery's give at the trading floor, though control goes on giving down to the battery's cut-out ([[UX-59]]).
+- During a price outage, the Batteries screen says "Prices differ too little" and Home says "The price gap is too small" ([[UX-60]]).
+- With battery modes on and no meter, or a meter that is a Home Assistant entity, a grid charge is not possible and nothing says so ([[UX-61]]).
+- On the Batteries screen, a charge the add-on refused in a cheap run reads as "Saves its power for ...", for up to 15 minutes ([[UX-62]]).
+- A Leftover solar battery with no capacity set never charges from the grid when a solar forecast is set, and nothing warns about it ([[UX-63]]).
+- The "How the modes work" box on the Batteries screen does not describe Cheap hours only ([[UX-64]]).
+- With battery modes on, Settings still shows "Trade on the price spread", which the modes ignore. A site with modes on and no price source starts, and the Batteries screen says "No prices, so it follows the house" without pointing to Settings ([[UX-65]]).
+- With battery modes off and several equal prices in a row, Home and the Forecast tab draw one price quarter, while the add-on trades every quarter of the run ([[UX-67]]).
+- Late in the day, the Forecast tab's "now" line and last bars sit over the axis labels at the right edge ([[UX-68]]).
+- The Forecast tab's level curve charges at each battery's full rating. Under a peak limit the levels it draws are too high and a charge block can end early (54.6 % shown against 39.7 % in a rig test) ([[UX-70]]).
+- The peak forecast check says maintenance charging is not kept under the peak limit when no peak forecast is set, but since 0.19.2 it is ([[UX-73]]).
+- The peak guard row can show the same figure twice, such as "at this rate 3 500 W, over 3 500 W". Also in 0.19.2 ([[UX-74]]).
+- If the inverter's setpoint entity appears in Home Assistant after the add-on has started, the page keeps saying "Inverter control: not found in Home Assistant" and the batteries say "An alarm stopped control" until a restart, though control runs ([[UX-75]]).
+- In the last minute of a 15-minute period, with Home Assistant readings 30 s late, the period can end about 80 W over the peak aim and over the limit: 3 530 W against a 3 450 W aim and a 3 500 W limit in a rig test with a 2 kW load added 45 s before the end. The peak guard sees the load too late to hold it back ([[SAFETY-133]]).
+- With Home Assistant readings 10 s late, the grid charge in a cheap run can swing by several kW. In a test the add-on asked for an 8.7 kW charge (9.6 kW on 0.20.0) ([[SAFETY-132]]).
+- A plan rebuilt while the battery levels are missing for a moment can drop a cheap run that has not started yet, so the battery does not charge that day. Seen in a replay of real prices, where it cost about EUR 0.40 of extra grid use; the Leftover solar change in 0.20.1 no longer triggers it in those replays, but the cause stays ([[OPT-37]]).
+- On a 5 s meter, Home Assistant readings 10 s late are not caught, and readings 15 s late only after about 4 minutes. With a changing load such as an oven or a kettle, 21 to 142 Wh can go to the grid in a simulation, against 2 to 27 Wh with readings on time ([[SAFETY-136]]).
+- With readings 10 to 15 s late, the hold can end in the middle of the delay and the swing can come back. Seen in rig tests with a 2 s and a 5 s meter ([[SAFETY-134]]).
+- With readings 10 s late on a 1 s meter, the grid can still move between -422 and +340 W while the batteries are held. With a very long delay (30 to 90 s) the request can swing by about 900 W every few seconds. Seen in review tests ([[SAFETY-130]]).
+- A battery that answers very slowly (10 s or more) can be taken for late Home Assistant readings and held, and the page then blames Home Assistant. A GoodWe battery settles in about 6 s and this has not been seen on one ([[SAFETY-131]]).
+- The page row for late readings reads awkwardly in English ("Home Assistant readings show requests about N seconds late, so control holds the batteries"), and the Dutch text misses a word ([[UX-78]]).
+- On a night grid charge held to the peak limit, the peak guard can stop the charge 1 to 3 s into a 15-minute period and keep it paused for that whole period. In a rig test this cost up to about 0.27 kWh of grid charge per run; it may come from the sped-up rig clock ([[SAFETY-135]]).
+- When the add-on stops, a write that takes more than 2 s can still land after the 0 W, and the 30 s safety timer on the ESPHome board then sets 0 W. After the Stop button, a cycle that had already decided can send its share (560 to 670 W) just after the 0 W; the next cycle sends 0 W again ([[SAFETY-138]]).
+- In the last hour of a cheap run, Home can draw a battery's grid charge up to an hour past the time control stops charging it. It only draws too much, never too little ([[UX-79]]).
+- A tomorrow solar forecast sensor that reports just after midnight with yesterday's value can be used as the new day's forecast for up to 12 hours. This has not been seen on a site ([[OPT-39]]).
+- During a cheap-hours charge, at some 15-minute boundaries the add-on sends 0 W for one tick ("no trade (headroom)") and then goes on. Seen in a rig test, in 5 of 8 cases; once, with a frozen battery reading, it left a battery at 0 W until 23:45 ([[OPT-40]]).
+
+### If you are crossing from a version older than 0.10.0
+
+`## 0.10.0` below can refuse an old config: `slew_w` above its limit, and the
+withdrawn `price_provider` ids `engie_dynamic`, `totalenergies_dynamic` and
+`eneco_eddy`. Read it before you update. Run `tools/predeploy_check.py` with the
+bare options (`jq '.data.options'`) first.
 
-- Each inverter is now reached through a driver, so another make can be added later. Nothing changes for a GoodWe site ([[SMA-2]]).
-- Home now draws today's charge from the grid for every hour the add-on will really charge, not only the run under way ([[UX-77]]).
-- When Home Assistant passes readings on late, control no longer swings on them: it waits until the battery shows its last power request, and the peak limit no longer asks for full power on them. The page says so, and if the readings stay too late every inverter goes to 0 W ([[SAFETY-128]]).
-- With a 5 s meter, readings 30 s late are now noticed within 100 seconds, not 3 minutes ([[SAFETY-129]]).
-- If one of the tomorrow solar forecast sensors stops updating in the afternoon, tomorrow's forecast now stays on the Forecast tab instead of vanishing until 20:00 ([[OPT-38]]).
 
 ## 0.20.1
 
@@ -63,7 +174,7 @@ Contents of this release, in merge order since 0.20.0 (`01e88a2`):
 - After the add-on restarts, the Home price chart shows no price for the earlier part of today, and the setup check can say "12 of 24 hours", though the prices are known ([[UX-48]]).
 - With battery modes on and only batteries on "Leftover solar", the Home price chart can mark a cheap period where no battery charges ([[UX-49]]).
 - On a phone, the bars of the Home price chart are too thin to tap one 15-minute period. The arrow keys work ([[UX-50]]).
-- Control acts on Home Assistant readings that arrive late. With readings 10 s behind, the give run can swing and send up to 1.9 kW to the grid for about 50 s in a rig test; with readings 30 s behind, a battery can charge from the grid in an expensive period. Also in 0.19.2. A fix is made for the next release and is not in 0.20.1 ([[SAFETY-128]]).
+- Control acts on Home Assistant readings that arrive late. With readings 10 s behind, the give run can swing and send up to 1.9 kW to the grid for about 50 s in a rig test; with readings 30 s behind, a battery can charge from the grid in an expensive period. Also in 0.19.2. The fix is not in 0.20.1; it ships in 0.21.0 ([[SAFETY-128]]).
 - In the last second of a 15-minute period, being a few watts over the aim can make the peak guard ask a battery for full power for one second. When a charge ends on a period edge, the last-second give can fade out over about 10 s, and a rig test exported up to 7.4 kW for about 8 s ([[SAFETY-124]]).
 - During the night grid charge, a 15-minute period can end 6 to 14 W over the peak aim, because the battery charges harder than asked. This was seen in simulation; a rig test saw 2 to 8 W ([[OPT-35]]).
 - The test rig could not bring back the false peak alarm that [[SAFETY-126]] fixes, so that fix is shown in simulation only. Watch the notifications for a few nights ([[TEST-35]]).

goodwe_controller/DECISIONS/SAFETY-137-last-write-is-zero.md

@@ -0,0 +1,21 @@
+# SAFETY-137 - the shutdown 0 W is the last write every unit hears
+
+SMA-10 made a hand-back release wait for a write already on its way
+(`_release_last`, `Inverter.inflight`). A GoodWe unit skipped that, and rig 5b
+saw a cycle write (-2 823 W) land after the shutdown 0 W and stay until relaunch.
+
+Now the 0 W of shutdown and of the Stop button is a *last* write
+(`_write_unit(last=True)`), for every driver:
+
+- It first waits, at most `SETTLE_BUDGET_S` (2 s), for the writes already on
+  its way to that unit (`_await_inflight`, shared with `_release_last`). A hung
+  write is not waited out and not cancelled; the 0 W goes anyway.
+- Once shutdown has begun (`stopping`), every other write (cycle, heartbeat,
+  safety stop) is dropped at the same place, right before the write is created.
+  That is the gate that keeps the control cycle quiet; the cycle itself needs
+  no cancelling.
+- Worst case for a GoodWe unit is 2 s + `WRITE_BUDGET_S` (4 s) = 6 s, the same
+  as `HAND_BACK_WORST_S`; the units are handled together.
+
+Not touched: the heartbeat's own timing, safety-stop paths, the maintenance
+abort (still a plain 0 W).

goodwe_controller/DECISIONS/SMA-10-two-idle-states.md

@@ -0,0 +1,62 @@
+# SMA-10 - two idle states: hold 0 W, or hand the inverter back
+
+**Status: for review.** Tests: `test_sma10_two_idle_states.py`. Source: SMA-9
+report sections 1.4, 3.2; owner decision 2026-10-20 (Q1, "as proposed").
+
+A unit is idle in one of two ways, and the driver says which:
+`Driver.hands_back`. **False (GoodWe):** the add-on holds 0 W, `release()` is
+`write(0)` and the Controller never calls it, so Stop keeps today's 0 W write and
+today's 0 W heartbeat. **True:** `release()` gives the unit back to whatever
+steers it by itself (SMA energy management), once, and then nothing is written
+to it until control starts again.
+
+**Why two.** When the add-on goes away (Stop, shutdown, SIGTERM, restart, task
+death, a config refusal) nobody is left to hold a number, so the unit goes back
+to its own controller. When the add-on itself decides to stop (sign trip, site
+sign, circulating power, a refused or non-finite write, missing readings,
+another writer, an inverter fault) it has just said it cannot trust that
+battery, and handing it to something else would let that something do what it
+likes with it. Those hold 0 W through `write(0)` for every unit, whatever its
+driver. Shadow mode on a unit that hands back uses `release()`: it must leave
+the unit alone, and 0 W would be a command.
+
+**Where.** `Controller.command_site_release()` sits beside `command_site_zero()`
+(unchanged). Stop and `shutdown()` call it; the two maintenance-abort paths keep
+zero (the add-on runs on, the sentence says 0 W for a moment). With no
+hand-back unit it is `command_site_zero()`. `_write_unit()` also refuses to write
+a hand-back unit while the add-on is idle (stopping, stopped, or shadow mode): it
+releases once and returns, so the heartbeat and the cycle's own "stopped" 0 W
+cannot reach it. A safety stop runs while control runs, so it falls through to
+the write. Start re-arms: `released` drops and `last_write` clears.
+
+**Bounds.** `RELEASE_BUDGET_S` equals `WRITE_BUDGET_S` (4 s): units are released
+together, so one slow unit costs the kill window no more than a hung GoodWe
+write does. A release at the bound is abandoned, not awaited. A release that
+raises, hangs or returns false leaves that unit un-handed (the next idle write
+tries again) and does not touch the others. Exit 78 before the Controller
+exists has no driver to release and keeps today's path.
+
+**Words.** Every sentence that said "set to 0 W" for the add-on going away or
+for shadow mode is built from the roster in `app/handback.py` (EN and NL): a
+roster with no hand-back unit gets None and keeps its old literal, so a GoodWe
+site sees no changed byte. A hand-back unit's words (`Driver.words`: `back`,
+`back_nl`) come from its driver; one without them gets "its own control" /
+"de eigen sturing" (the article as in the generic clause; PR #239 review
+comment 2495, not the brief). MQTT `status` is unchanged; the Home battery
+row of a handed-back unit says "Back under SMA control" and carries
+`handed_back`.
+
+**Not done here (SMA-4, SMA-5, SMA-11):** any SMA/FoxESS driver, the read-back
+after `release()`, per-driver timing, DOCS.md's safety model and the
+"control stalled" sentence, the site-level "Held at 0 W" tiles in shadow mode on
+a mixed roster, and the MQTT per-unit setpoint of a handed-back unit (it still
+publishes 0).
+
+**After a failed release** (returns False, raises or hangs past the bound) the
+unit gets one `write(0)` through `Driver.release_fallback()` (default
+`write(0)`; a driver where 0 W is not always safe overrides it), then nothing:
+a repeated 0 W would keep resetting the inverter's own fallback timer, so after
+that the unit is left to its own fallback. The release is retried once per
+heartbeat; one error line and one action-log event per failure streak, one line
+on recovery. Worst case at shutdown is `RELEASE_BUDGET_S` + `FALLBACK_BUDGET_S`
+(6 s).

goodwe_controller/app/drivers.py

@@ -77,7 +77,13 @@ class Driver:
     writer_key = ""
     #: the brand word the per-driver sentences and device names use
     brand = ""
-    #: per-driver sentences (SMA-10 and later). Empty until a caller needs one.
+    #: SMA-10. Does `release()` give the inverter BACK to something that steers
+    #: it by itself (SMA energy management)? False: `release()` is `write(0)`,
+    #: the add-on goes on holding 0 W, and the Controller never calls it.
+    hands_back = False
+    #: per-driver sentences. A driver that hands back says whose control the
+    #: unit returns to: `{"back": "SMA control", "back_nl": "de sturing van SMA"}`
+    #: ("goes back to SMA control"). Missing words fall back to a plain phrase.
     words: dict = {}
     #: how long all-rejected writes last before the unit stops being live
     link_stale_s = GOODWE_LINK_STALE_S
@@ -145,7 +151,21 @@ class Driver:
         raise NotImplementedError
 
     async def release(self) -> bool:
-        """Stop steering this inverter. For a driver with nothing better, 0 W."""
+        """Stop steering this inverter. For a driver with nothing better, 0 W.
+
+        SMA-10. Only a driver with `hands_back = True` has this called by the
+        Controller, and only when the add-on goes away (Stop, shutdown, restart,
+        task death) or sits in shadow mode. After it the Controller writes
+        nothing more to the unit until control starts again. A safety stop is
+        never a release: that is `write(0)`."""
+        return await self.write(0.0)
+
+    async def release_fallback(self) -> bool:
+        """SMA-10 round 2. What to send, ONCE, when `release()` has failed
+        (False, raised, or hung past the bound), so the unit does not carry its
+        last command while nothing else steers it. Default: `write(0)`. It is
+        not repeated: a repeat would keep resetting the inverter's own fallback
+        timer. A driver for which 0 W is not always a safe hold overrides this."""
         return await self.write(0.0)
 
     async def probe(self) -> Probe:
@@ -159,7 +179,8 @@ class GoodWeEsphomeDriver(Driver):
     A transcription of what `main.py` and `selfconfig.py` did inline: `limits()`
     is `hass.limits(setpoint)`, `read()` is `hass.number(soc)` then
     `hass.number(batt, invert)`, `write()` is `hass.set_number(setpoint, w)`.
-    `release()` is `write(0)`: the board's own watchdog is what hands back.
+    `release()` is `write(0)` and `hands_back` is False: the board's own watchdog
+    is what hands back, so after Stop the unit keeps its 0 W write and heartbeat.
     """
 
     name = DEFAULT_DRIVER

goodwe_controller/app/handback.py

@@ -0,0 +1,386 @@
+"""SMA-10: the two idle states, in words.
+
+A unit is either HELD at 0 W (GoodWe: the add-on goes on writing 0 W) or
+HANDED BACK (its driver has `hands_back = True`: `release()` gives it back to
+whatever steers it by itself, and the add-on then writes nothing to it). So every
+sentence that said "every inverter is set to 0 W" for the add-on going away or
+for shadow mode has to be built from the roster. DECISIONS/SMA-10-two-idle-
+states.md.
+
+THE RULE FOR EVERY BUILDER HERE: a roster with no hand-back unit gets None, and
+the caller then uses the sentence it always used, untouched. So a GoodWe-only
+site cannot see a changed byte; test_sma10_two_idle_states.py renders each one
+and compares it with the literal from before this card.
+
+The words for a hand-back unit come from its driver (`Driver.words`), not from
+here: `back` is "SMA control" in "goes back to SMA control", `back_nl` is the
+Dutch noun phrase after "terug naar". A driver without them gets a plain,
+brand-free phrase.
+
+Safety stops and refusals are not in this file on purpose: they hold 0 W for
+every unit, and their sentences say so.
+"""
+
+from __future__ import annotations
+
+import re
+from dataclasses import dataclass
+
+_BACK_EN = "its own control"
+_BACK_NL = "de eigen sturing"
+
+
+@dataclass(frozen=True)
+class Unit:
+    name: str
+    hands_back: bool = False
+    back_en: str = _BACK_EN
+    back_nl: str = _BACK_NL
+
+
+def unit_of(inv) -> Unit:
+    """One roster entry's view: its name, and (for a hand-back driver) the
+    words of whose control it returns to."""
+    drv = inv.driver
+    back = bool(getattr(drv, "hands_back", False))
+    words = getattr(drv, "words", None) or {}
+    return Unit(str(inv.name), back,
+                str(words.get("back") or _BACK_EN),
+                str(words.get("back_nl") or _BACK_NL))
+
+
+def units_of(inverters) -> tuple:
+    return tuple(unit_of(i) for i in inverters)
+
+
+# The roster of the Controller that is running, for the callers that have no
+# Controller in hand (the page, the banner). One process runs one Controller.
+_CURRENT: list = [()]
+
+
+def set_roster(units) -> None:
+    _CURRENT[0] = tuple(units)
+
+
+def current() -> tuple:
+    return _CURRENT[0]
+
+
+def active(units) -> bool:
+    """Is any unit handed back? False is every GoodWe-only roster."""
+    return any(u.hands_back for u in units)
+
+
+# --------------------------------------------------------------------------- #
+# The grammar. English and Dutch, a few verb forms each.
+# --------------------------------------------------------------------------- #
+def _join(names, lang) -> str:
+    names = list(names)
+    word = " en " if lang == "nl" else " and "
+    if len(names) <= 1:
+        return "".join(names)
+    return ", ".join(names[:-1]) + word + names[-1]
+
+
+def _forms(lang):
+    """kind -> (zero template, back template); `{n}` the names, `{b}` the words.
+    `one`/`many` pick the verb by how many units the clause is about."""
+    if lang == "nl":
+        return {
+            "set": (("{n} gaat naar 0 W", "{n} gaan naar 0 W"),
+                    ("{n} gaat terug naar {b}", "{n} gaan terug naar {b}")),
+            "at": (("{n} op 0 W",) * 2, ("{n} onder {b}",) * 2),
+            "is": (("{n} staat op 0 W", "{n} staan op 0 W"),
+                   ("{n} staat onder {b}", "{n} staan onder {b}")),
+            "stays": (("{n} blijft op 0 W", "{n} blijven op 0 W"),
+                      ("{n} blijft onder {b}", "{n} blijven onder {b}")),
+        }
+    return {
+        "set": (("{n} is set to 0 W", "{n} are set to 0 W"),
+                ("{n} goes back to {b}", "{n} go back to {b}")),
+        "at": (("{n} at 0 W",) * 2, ("{n} under {b}",) * 2),
+        "is": (("{n} is at 0 W", "{n} are at 0 W"),
+               ("{n} is under {b}", "{n} are under {b}")),
+        "stays": (("{n} stays at 0 W", "{n} stay at 0 W"),
+                  ("{n} stays under {b}", "{n} stay under {b}")),
+    }
+
+
+def _groups(units, lang):
+    """`(zero names, [(names, back words)])`: the held units, and the handed-back
+    ones grouped by whose control they return to, in roster order."""
+    zeros = [u.name for u in units if not u.hands_back]
+    groups: dict = {}
+    for u in units:
+        if u.hands_back:
+            groups.setdefault(u.back_nl if lang == "nl" else u.back_en,
+                              []).append(u.name)
+    return zeros, [(names, back) for back, names in groups.items()]
+
+
+# A clause may not eat the sentence it sits in: STYLE.md allows 25 words, and
+# the longest tail after a clause is about 11.
+CLAUSE_MAX_WORDS = 14
+
+
+def _count_txt(n, lang) -> str:
+    if lang == "nl":
+        return f"{n} omvormer" if n == 1 else f"{n} omvormers"
+    return f"{n} inverter" if n == 1 else f"{n} inverters"
+
+
+def _clause(units, lang, kind, sep, generic, counted) -> str:
+    forms = _forms(lang)[kind]
+    zeros, groups = _groups(units, lang)
+    if generic:                 # one group, and no make named
+        names = [n for g, _b in groups for n in g]
+        own = ("de eigen sturing" if lang == "nl" else
+               "their own control" if len(names) > 1 else "its own control")
+        groups = [(names, own)] if names else []
+    subject = ("de omvormers", "de omvormer") if lang == "nl" else (
+        "the inverters", "the inverter")
+    parts = []
+    if zeros:
+        parts.append(forms[0][1 if len(zeros) > 1 else 0].format(
+            n=(str(len(zeros)) if groups else _count_txt(len(zeros), lang))
+            if counted else _join(zeros, lang)))
+    for names, back in groups:
+        if not zeros and len(groups) == 1:
+            names_txt = subject[0 if len(names) > 1 else 1]
+        elif counted:
+            # the bare number after a counted first clause: "1 inverter is set
+            # to 0 W and 2 go back to their own control"
+            names_txt = (str(len(names)) if zeros
+                         else _count_txt(len(names), lang))
+        else:
+            names_txt = _join(names, lang)
+        parts.append(forms[1][1 if len(names) > 1 else 0].format(
+            n=names_txt, b=back))
+    if sep:
+        return sep.join(parts)
+    word = " en " if lang == "nl" else " and "
+    return (", ".join(parts[:-1]) + word + parts[-1]) if len(parts) > 1 \
+        else "".join(parts)
+
+
+def clause(units, lang, kind, sep=None) -> str:
+    """One clause about the whole roster, `kind` one of set/at/is/stays.
+
+    Held units first, then the handed-back ones, joined by "and" (or `sep`).
+    When EVERY unit is handed back to the same control the subject is "the
+    inverters", not their names, as the card's table has it.
+
+    A long roster would break the 25-word rule, so a clause over
+    CLAUSE_MAX_WORDS is said again without naming the make (one "own control"
+    for all), and then by counting units instead of naming them."""
+    text = _clause(units, lang, kind, sep, False, False)
+    if sep or _words(text) <= CLAUSE_MAX_WORDS:
+        return text
+    text = _clause(units, lang, kind, sep, True, False)
+    if _words(text) <= CLAUSE_MAX_WORDS:
+        return text
+    return _clause(units, lang, kind, sep, True, True)
+
+
+def _cap(text) -> str:
+    return text[:1].upper() + text[1:]
+
+
+def _bi(en, nl):
+    from .messages import Bi
+    return Bi(en, nl)
+
+
+def _words(text) -> int:
+    return len([w for w in re.findall(r"\S+", text)
+                if re.search(r"[A-Za-z0-9]", w)])
+
+
+# --------------------------------------------------------------------------- #
+# The sentences. Each returns None for a roster with no hand-back unit.
+# --------------------------------------------------------------------------- #
+def stop_dialog(units, lang):
+    """Stop control?  (was "Every inverter is set to 0 W until you start
+    control again.")"""
+    if not active(units):
+        return None
+    c = clause(units, lang, "set")
+    return (f"{_cap(c)} tot u de regeling opnieuw start." if lang == "nl"
+            else f"{_cap(c)} until you start control again.")
+
+
+def restart_dialog(units, lang):
+    """Restart now? / Save and restart? (live)"""
+    if not active(units):
+        return None
+    c = clause(units, lang, "set")
+    return (f"{_cap(c)} terwijl de add-on herstart, daarna gelden de nieuwe "
+            f"instellingen." if lang == "nl" else
+            f"{_cap(c)} while the add-on restarts, and then the new settings "
+            f"apply.")
+
+
+def restart_dialog_shadow(units, lang):
+    """Save and restart? when shadow mode keeps the units idle afterwards."""
+    if not active(units):
+        return None
+    c = clause(units, lang, "set")
+    return (f"{_cap(c)} terwijl de add-on herstart, en de schaduwmodus houdt "
+            f"het zo." if lang == "nl" else
+            f"{_cap(c)} while the add-on restarts, and shadow mode keeps it "
+            f"that way.")
+
+
+def setup_dialog_shadow(units, lang):
+    """Save and restart? in setup, shadow mode on."""
+    if not active(units):
+        return None
+    c = clause(units, lang, "at")
+    return (f"De add-on herstart met deze instellingen, en de schaduwmodus "
+            f"houdt {c}." if lang == "nl" else
+            f"The add-on restarts with these settings, and shadow mode keeps "
+            f"{c}.")
+
+
+def control_stopped(units, lang):
+    """The page's control line when stopped."""
+    if not active(units):
+        return None
+    c = clause(units, lang, "is")
+    return (f"De regeling is gestopt. {_cap(c)}." if lang == "nl"
+            else f"Control is stopped. {_cap(c)}.")
+
+
+def control_shadow(units, lang):
+    """The page's control line in shadow mode."""
+    if not active(units):
+        return None
+    c = clause(units, lang, "stays")
+    return (f"Schaduwmodus: {c}." if lang == "nl" else f"Shadow mode: {c}.")
+
+
+def attn_shadow_body(units, lang):
+    """The attention card's body in shadow mode."""
+    if not active(units):
+        return None
+    c = clause(units, lang, "stays")
+    return (f"De add-on beslist alles, maar {c}." if lang == "nl" else
+            f"The add-on decides everything, but {c}.")
+
+
+def shadow_state(units, lang, many=True):
+    """The tail of a notification: "Shadow mode is on, so <this>." For the
+    three output-clamp sentences that said every inverter stays at 0 W."""
+    if not active(units):
+        return None
+    return clause(units, lang, "stays")
+
+
+def banner_stopped(units):
+    """Stopped. 12 words at most (STYLE.md)."""
+    if not active(units):
+        return None
+    out = {}
+    for lang, stopped in (("en", "Stopped"), ("nl", "Gestopt")):
+        text = f"{stopped} — {clause(units, lang, 'at', sep=', ')}"
+        if _words(text) > 12:
+            text = _banner_counts(units, lang, stopped)
+        out[lang] = text
+    return _bi(out["en"], out["nl"])
+
+
+def _banner_counts(units, lang, stopped) -> str:
+    """The long-roster form: how many, not which."""
+    zeros, groups = _groups(units, lang)
+    if len(groups) == 1:
+        back = groups[0][1]
+        n_back = len(groups[0][0])
+        if lang == "nl":
+            held = f"{len(zeros)} op 0 W, " if zeros else ""
+            return f"{stopped} — {held}{n_back} onder {back}"
+        held = f"{len(zeros)} at 0 W, " if zeros else ""
+        return f"{stopped} — {held}{n_back} under {back}"
+    return (f"{stopped} — omvormers op 0 W of teruggegeven" if lang == "nl"
+            else f"{stopped} — inverters at 0 W or handed back")
+
+
+def banner_shadow(units):
+    """Shadow mode, nothing standing. The GoodWe sentence adds "Inverters stay
+    at 0 W." which is false for a unit that hands back, and a banner is 12
+    words, so the unit-by-unit state is left to the control line."""
+    if not active(units):
+        return None
+    return _bi("Shadow mode: the battery is not controlled.",
+               "Schaduwmodus: de batterij wordt niet geregeld.")
+
+
+def hint_shadow_on(units):
+    """"Shadow mode on, inverters stay at 0 W" for the Last event line."""
+    if not active(units):
+        return None
+    return "Shadow mode on, " + clause(units, "en", "at", sep=", ")
+
+
+def unit_state(unit, lang):
+    """One handed-back unit's own state, in place of "Held at 0 W"."""
+    if lang == "nl":
+        return f"Terug onder {unit.back_nl}"
+    return f"Back under {unit.back_en}"
+
+
+def log_shutdown(units):
+    """The INFO line at shutdown (was "shutting down - commanding 0 W on every
+    inverter")."""
+    if not active(units):
+        return None
+    zeros, groups = _groups(units, "en")
+    held = f"commanding 0 W on {_join(zeros, 'en')}" if zeros else ""
+    back = " and ".join(f"handing back {_join(n, 'en')} to {b}"
+                        for n, b in groups)
+    return "shutting down - " + " and ".join(x for x in (held, back) if x)
+
+
+def task_died_state(units) -> str:
+    """The part of the CRITICAL line after "so" when the control task dies.
+    For a roster with no hand-back unit it is the sentence it always was."""
+    if not active(units):
+        return "every inverter is set to 0 W"
+    zeros, groups = _groups(units, "en")
+    backs = [n for names, _b in groups for n in names]
+    parts = []
+    if zeros:
+        parts.append(f"{_join(zeros, 'en')} "
+                     f"{'are' if len(zeros) > 1 else 'is'} set to 0 W")
+    parts.append(f"{_join(backs, 'en')} "
+                 f"{'are' if len(backs) > 1 else 'is'} handed back")
+    return " and ".join(parts)
+
+
+# --------------------------------------------------------------------------- #
+# The page words: the ui_text sentences that move with the roster, by language.
+# --------------------------------------------------------------------------- #
+def overlay(units) -> dict:
+    """`{lang: nested dict}` of ui_text paths to replace; {} when no unit is
+    handed back, so the page is the file as it always was."""
+    if not active(units):
+        return {}
+    out = {}
+    for lang in ("en", "nl"):
+        out[lang] = {
+            "home": {"dialog": {"stop": {
+                "description": stop_dialog(units, lang)}}},
+            "settings": {
+                "dialog": {"description": restart_dialog(units, lang)},
+                "setup": {
+                    "dialog": {"description":
+                               restart_dialog_shadow(units, lang)},
+                    "dialog_live": {"description":
+                                    restart_dialog(units, lang)},
+                    "dialog_setup": {"description":
+                                     setup_dialog_shadow(units, lang)}}},
+            "home_words": {
+                "attn_shadow_body": attn_shadow_body(units, lang),
+                "control": {"shadow": control_shadow(units, lang),
+                            "stopped": control_stopped(units, lang)}},
+        }
+    return out

goodwe_controller/app/homeview.py

@@ -19,7 +19,7 @@ section at the bottom and is held to STYLE.md by test_messages.py.
 import contextlib
 from datetime import datetime, timedelta, timezone
 
-from . import arbitrage, cheaproll, messages, peakguard, priceruns, uitext
+from . import arbitrage, cheaproll, handback, messages, peakguard, priceruns, uitext
 from .dayplan import EFF
 from .maintenance import CHARGE as M_CHARGE, DRAIN as M_DRAIN, HOLD as M_HOLD
 from .maintenance import IDLE as M_IDLE, next_slot_start
@@ -936,6 +936,13 @@ def battery_rows(c, shadow, running, held=False):
                              else other, at=at,
                              **plan_words(c, inv.name, why)),
         })
+        if getattr(inv, "released", False):
+            # SMA-10. A unit handed back says so, in its driver's words, not
+            # "Held at 0 W": nothing is written to it. The key exists only for
+            # such a unit, so a GoodWe-only page is unchanged.
+            rows[-1]["now"] = handback.unit_state(handback.unit_of(inv),
+                                                  _LANG[0])
+            rows[-1]["handed_back"] = True
         if modes_on:
             # OPT-11 P1: the battery's switch and mode, for the Batteries
             # screen. Only with battery modes on, so the page is unchanged
@@ -1211,6 +1218,9 @@ _WORDS: dict = {}
 
 def _hw() -> dict:
     lang = _LANG[0]
+    if _WORDS.get("") != uitext.generation():     # SMA-10: the roster's words moved
+        _WORDS.clear()
+        _WORDS[""] = uitext.generation()
     if lang not in _WORDS:
         _WORDS[lang] = uitext.words(lang)
     return _WORDS[lang]

goodwe_controller/app/inverter.py

@@ -275,6 +275,21 @@ class Inverter:
         self.target = 0.0
         self.last_write = None
         self.last_write_at = None
+        # SMA-10. True from the moment this unit is handed back (`release()`)
+        # until control starts again. While it is True nothing is written to the
+        # unit - not the heartbeat, not the cycle - so the unit's own
+        # controller keeps what it was given. Only a driver with
+        # `hands_back = True` ever sets it.
+        self.released = False
+        # SMA-10. Writes to a hand-back driver that are on their way (see
+        # Controller._write_unit), so the release can wait for them and be LAST.
+        self.inflight: set = set()
+        # SMA-10 round 2. A failed hand-back: how many tries in a row failed
+        # (the log is written at the first and on recovery only), when the next
+        # try is due (monotonic s), and whether the one fallback 0 W was sent.
+        self.release_fails = 0
+        self.release_retry_at = 0.0
+        self.release_zero_sent = False
         self.last_write_ok = None
         # ⚠️ TWO TIMESTAMPS, NOT ONE FLAG. `last_write_ok` is the last write's
         # verdict and it flips on a single transient 400; liveness needs a RUN

goodwe_controller/app/main.py

@@ -67,6 +67,7 @@ from . import freshness
 from . import lateness
 from . import dayview, homeview
 from .daycurve import SolarToday
+from . import handback
 from . import messages
 from .freeze import (
     FreezeWatchdog, FreezeWatchdogConfig, looks_frozen, rail_unreachable, rail_w,
@@ -89,6 +90,7 @@ from . import peakguard
 from . import packshare
 from . import pv as pv_read
 from . import shadow
+from . import uitext
 from .p1 import P1Ingest, build_source, is_enabled
 from .price import Absence, Uncertainty, brussels, price_option, provider_configured
 from .price import required_spread as price_required_spread
@@ -138,6 +140,26 @@ __all__ = ["UNIT_A", "Controller", "amain", "main"]
 # the re-issue happens by itself) than hold the control loop for ten seconds.
 WRITE_BUDGET_S = 4.0
 
+# SMA-10. The same bound for handing a unit back (`driver.release()`). It is the
+# time the shutdown path already allows one 0 W write, and the units are
+# released CONCURRENTLY, so one slow or hung unit costs the wind-down no more
+# than a hung GoodWe write does today: the Supervisor's kill window is not lost
+# to it. A release still running at the bound is abandoned, not awaited.
+RELEASE_BUDGET_S = WRITE_BUDGET_S
+
+# SMA-10 round 2. The one fallback write after a failed release (default 0 W,
+# `Driver.release_fallback()`). Worst case for a unit whose release hangs:
+# RELEASE_BUDGET_S + FALLBACK_BUDGET_S = 6 s, against the Supervisor's 10 s.
+FALLBACK_BUDGET_S = 2.0
+HAND_BACK_WORST_S = RELEASE_BUDGET_S + FALLBACK_BUDGET_S
+
+# SAFETY-137. How long a LAST write (the Stop 0 W, the shutdown 0 W, a release)
+# waits for a write already on its way to the same unit. Half the release
+# budget, as `_release_last` always waited. For a GoodWe unit that is
+# SETTLE_BUDGET_S + WRITE_BUDGET_S = 6 s at worst, which is HAND_BACK_WORST_S:
+# the wind-down is no slower than SMA-10's worst case.
+SETTLE_BUDGET_S = RELEASE_BUDGET_S / 2
+
 # SAFETY-34: a Core-only restart wipes persistent_notification and does NOT
 # restart this add-on (measured on TEST-23), so a latched alarm is re-asserted
 # this often. Why: goodwe docs/DECISIONS.md, SAFETY-34.
@@ -561,6 +583,10 @@ class Controller:
         self.store_migration = migrate_unit_keys(
             store, _roster_names[0], _roster_names)
         self.inverters = build_roster(opts, store, sign_cfg, delivery_cfg)
+        # SMA-10. Which units hand back decides what the page says about Stop,
+        # restart and shadow mode. A GoodWe-only roster adds nothing.
+        handback.set_roster(handback.units_of(self.inverters))
+        uitext.set_idle(handback.overlay(handback.current()))
         # ⚠️ CFG-04. SAY WHICH SHAPE IS IN FORCE, BECAUSE THE OTHER ONE'S KEYS
         # ARE STILL SITTING IN THE UI. A declared `inverters:` roster reads none
         # of `soc_entity`, `batt_entity`, `batt_invert` or `max_w`, and an
@@ -4001,7 +4027,7 @@ class Controller:
         return rec.authorises(inv.name, value, self.alloc_tick)
 
     async def write_setpoint(self, value: float, *, force: bool = False,
-                             unit=None) -> None:
+                             unit=None, last: bool = False) -> None:
         """Put `value` on ONE inverter, or - with `unit=None` - on all of them.
 
         ⚠️ `unit=None` IS FOR A NUMBER THAT IS NOT A SHARE. The stop button,
@@ -4040,12 +4066,126 @@ class Controller:
             targets = [unit]
         if not targets:
             return
-        await asyncio.gather(*(self._write_unit(inv, value, force=force)
+        await asyncio.gather(*(self._write_unit(inv, value, force=force,
+                                                last=last)
                                for inv in targets))
 
-    async def _write_unit(self, inv, value: float, *, force: bool = False) -> None:
+    async def _await_inflight(self, inv, budget_s: float) -> None:
+        """Wait, at most `budget_s`, for the writes already on their way to
+        `inv` (SAFETY-137: every driver, GoodWe too). A write still running at
+        the bound is left alone, not cancelled: its own WRITE_BUDGET_S ends it."""
+        pending = [t for t in inv.inflight if not t.done()]
+        if pending:
+            await asyncio.wait(pending, timeout=budget_s)
+
+    async def _release_last(self, inv) -> bool:
+        """`release()`, after a write already on its way to `inv` has finished
+        (at most half the budget is spent waiting for it), so the release is the
+        LAST thing the unit hears and a late write cannot undo it."""
+        await self._await_inflight(inv, SETTLE_BUDGET_S)
+        return await self._driver(inv).release()
+
+    async def _hand_back(self, inv, *, force: bool = False) -> bool:
+        """SMA-10. Give ONE unit back: exactly one `release()`, then nothing.
+
+        True when the unit is handed back (now, or already). Never raises: a
+        driver that raises or hangs is logged and the unit is tried again on the
+        next idle write, and it cannot stop a sibling being released or zeroed.
+
+        ⚠️ `released` IS SET BEFORE THE FIRST AWAIT. A second caller (the
+        heartbeat while the Stop button is mid-release) then sees it and does
+        nothing, so a unit gets one `release()` and not two. If the release
+        did not take, the flag goes back down and the unit stays un-handed
+        until a later idle write tries again.
+
+        ⚠️ IT IS NOT A WRITE: no `note_write`, no `last_write`, so a hand-back
+        cannot be read as a link that answered. `last_write` is cleared so the
+        first write after control starts again is always sent.
+        """
+        if inv.released:
+            return True
+        if not inv.driver.configured():
+            return False
+        # After a failure the next try waits one heartbeat, so a hung release
+        # costs a cycle its 4 s once per heartbeat, not on every cycle. The
+        # Stop button and shutdown (`force`) always try.
+        now_m = time.monotonic()
+        if not force and now_m < inv.release_retry_at:
+            return False
+        inv.released = True
+        why = ""
+        try:
+            ok = bool(await _bounded(self._release_last(inv),
+                                     RELEASE_BUDGET_S))
+        except (asyncio.TimeoutError, TimeoutError):
+            ok, why = False, f"took over {RELEASE_BUDGET_S:.0f} s"
+        except Exception as err:  # noqa: BLE001 - one unit never stops the rest
+            ok, why = False, f"{type(err).__name__}: {err}"
+        if ok:
+            inv.last_write = None
+            if inv.release_fails:
+                _LOG.info("Handing back %s worked again after %d failed "
+                          "tries.", inv.name, inv.release_fails)
+            inv.release_fails = 0
+            inv.release_retry_at = 0.0
+            inv.release_zero_sent = False
+            self.log_event(f"{inv.name}: handed back",
+                           hint=messages.hint("handed_back", unit=inv.name))
+            return True
+        inv.released = False
+        inv.release_fails += 1
+        inv.release_retry_at = now_m + float(self.o.get("heartbeat_s", 10))
+        _LOG.debug("Handing back %s failed (try %d): %s", inv.name,
+                   inv.release_fails, why)
+        if inv.release_fails == 1:          # one line per failure streak
+            _LOG.error("Handing back %s failed, so it is sent 0 W once and "
+                       "handing back is tried again.", inv.name)
+            self.log_event(f"{inv.name}: hand-back failed",
+                           hint=messages.hint("hand_back_failed", unit=inv.name))
+        if not inv.release_zero_sent:
+            # ⚠️ ONCE. The unit must not keep carrying its last command, but a
+            # 0 W re-sent on every try would reset the inverter's own fallback
+            # timer for ever. The driver says what the one write is.
+            inv.release_zero_sent = True
+            try:
+                if await _bounded(self._driver(inv).release_fallback(),
+                                  FALLBACK_BUDGET_S):
+                    inv.last_write = 0.0
+            except Exception as err:  # noqa: BLE001
+                _LOG.debug("The fallback write to %s failed: %r", inv.name, err)
+        return False
+
+    async def _write_unit(self, inv, value: float, *, force: bool = False,
+                          last: bool = False) -> None:
         if not inv.driver.configured():
             return
+        # --- SMA-10: A UNIT THAT HANDS BACK IS NOT WRITTEN WHILE THE ADD-ON IS
+        # IDLE. Idle is: shutting down, control stopped, or shadow mode. The
+        # unit is released once and then nothing is written to it - not the
+        # heartbeat, not the cycle's "stopped" 0 W - so its own controller keeps
+        # it. This is the passive half; `command_site_release()` is the active
+        # one, for the moment the add-on goes away.
+        #
+        # ⚠️ A SAFETY STOP IS NOT IDLE. It happens while control runs (`auto`,
+        # not shadow), so it falls through to the 0 W write below: the add-on's
+        # own decision to hold 0 W is never turned into a hand-back.
+        #
+        # ⚠️ AND CONTROL STARTING AGAIN RE-ARMS THE UNIT: the flag drops and
+        # `last_write` is cleared, so the first write goes out whatever it is.
+        # `stopping` never re-arms: a shutdown in progress stays handed back.
+        if inv.driver.hands_back:
+            if self.stopping or self.shadow or not self.auto:
+                await self._hand_back(inv)
+                return
+            if inv.released or inv.release_fails or inv.release_zero_sent:
+                # Control has the unit again: forget the hand-back, and any
+                # failed streak with it, so the next Stop starts clean (its own
+                # one 0 W, its own error line and event).
+                inv.released = False
+                inv.last_write = None
+                inv.release_fails = 0
+                inv.release_retry_at = 0.0
+                inv.release_zero_sent = False
         entity = inv.driver.actuator_id()       # for the log line below
 
         # --- SAFETY-03: THE CLAMP, AND IT IS ON THE ONLY PATH TO THE WIRE -----
@@ -4159,6 +4299,21 @@ class Controller:
                        value, inv.name, shadow.WIRE_W)
             value = shadow.WIRE_W
 
+        # --- SAFETY-137: THE 0 W THAT ENDS THINGS IS THE LAST WRITE THE UNIT
+        # HEARS. `last` is the Stop 0 W and the shutdown 0 W (and nothing else).
+        # It first waits, bounded, for a write already on its way to this unit,
+        # so that write cannot land after it. And once shutdown has begun every
+        # other write (cycle, heartbeat, a safety stop) is dropped here: the
+        # check sits right before the write is created with no await between,
+        # so a write that starts after it cannot exist, and one that started
+        # before is in `inflight` for the wait above. The idle gate for a
+        # hand-back unit is higher up and does the same for those.
+        if last:
+            await self._await_inflight(inv, SETTLE_BUDGET_S)
+        elif self.stopping:
+            _LOG.debug("Shutting down, so %+.0f W to %s is not sent.",
+                       value, inv.name)
+            return
         changed = (inv.last_write is None or value != inv.last_write)
         if not (changed or force):
             return
@@ -4169,8 +4324,13 @@ class Controller:
         # tick by itself: `last_write` is updated only on an ACCEPTED write, so
         # `changed` is still true.
         try:
-            ok = await asyncio.wait_for(self._driver(inv).write(value),
-                                        timeout=WRITE_BUDGET_S)
+            _w = self._driver(inv).write(value)
+            # SMA-10 / SAFETY-137: kept for every driver, so a release or a last
+            # 0 W can wait for it (`_await_inflight`).
+            _w = asyncio.ensure_future(_w)
+            inv.inflight.add(_w)
+            _w.add_done_callback(inv.inflight.discard)
+            ok = await asyncio.wait_for(_w, timeout=WRITE_BUDGET_S)
         except (asyncio.TimeoutError, TimeoutError):
             ok = False
             _LOG.error("Sending %+.0f W to %s (%s) took over %.0f s and was "
@@ -6786,9 +6946,10 @@ class Controller:
             self.log_event("REFUSED: " + problems[0],
                            hint=messages.hint("refused"))
             # Signal, then return WITHOUT entering the loop. amain() wakes
-            # on this, runs the normal wind-down (which commands 0 W) and
-            # re-raises ConfigRefused afterwards, so the exit code is 78 and
-            # the inverter is left at zero rather than latched.
+            # on this, runs the normal wind-down (which commands 0 W, or hands
+            # back a unit whose driver does: SMA-10) and re-raises
+            # ConfigRefused afterwards, so the exit code is 78 and the
+            # inverter is left at zero rather than latched.
             self.stop_event.set()
             return
 
@@ -7052,11 +7213,43 @@ class Controller:
     async def shutdown(self) -> None:
         """Deterministic wind-down. Do not skip this."""
         self.stopping = True
-        _LOG.info("shutting down - commanding 0 W on every inverter")
-        await self.command_site_zero()
+        _LOG.info(handback.log_shutdown(handback.current())
+                  or "shutting down - commanding 0 W on every inverter")
+        await self.command_site_release()
         self.mqtt.close()
 
-    async def command_site_zero(self) -> None:
+    async def command_site_release(self) -> None:
+        """SMA-10. The add-on is going away (Stop, shutdown, restart, task
+        death, a config refusal): every unit that hands back is given back, and
+        every other unit is held at 0 W exactly as `command_site_zero()` does.
+
+        ⚠️ THE SAFETY STOPS AND REFUSALS DO NOT COME HERE. A sign trip, a
+        refused write, a missing reading, another writer: those are the add-on's
+        own decisions and hold 0 W through `write(0)` for EVERY unit, handed-back
+        drivers included. `command_site_zero()` is that, and it is unchanged. A
+        unit the add-on has just declared it cannot trust must not be handed to
+        something else that will then do what it likes with the battery.
+
+        ⚠️ A ROSTER WITH NO HAND-BACK UNIT IS `command_site_zero()`, line for
+        line: GoodWe's release is its 0 W write, so Stop keeps today's write
+        and today's heartbeat.
+
+        ⚠️ ONE UNIT'S FAILURE IS ITS OWN. `_hand_back()` never raises and is
+        bounded by RELEASE_BUDGET_S; the units run concurrently, so the whole
+        call takes no longer than its slowest bound.
+        """
+        if not any(inv.driver.hands_back for inv in self.inverters):
+            await self.command_site_zero(last=True)
+            return
+        self.target = 0.0
+        for inv in self.inverters:
+            inv.target = 0.0
+        await asyncio.gather(*(
+            self._hand_back(inv, force=True) if inv.driver.hands_back
+            else self._write_unit(inv, 0.0, force=True, last=True)
+            for inv in self.inverters))
+
+    async def command_site_zero(self, *, last: bool = False) -> None:
         """Every inverter to 0 W, and every inverter's TARGET to 0 W with it.
 
         ⚠️ THE SECOND HALF IS NOT BOOKKEEPING, AND IT IS A HAZARD DEV-02
@@ -7078,7 +7271,7 @@ class Controller:
         self.target = 0.0
         for inv in self.inverters:
             inv.target = 0.0
-        await self.write_setpoint(0.0, force=True)
+        await self.write_setpoint(0.0, force=True, last=last)
 
     # -- UI ------------------------------------------------------------------
     def checks(self, when: datetime | None = None) -> list:
@@ -8011,7 +8204,9 @@ class Controller:
                 # Zeroing `self.target` alone would leave each unit's last share
                 # standing for its next heartbeat to re-emit, which an operator
                 # would read as the stop button not working.
-                await self.command_site_zero()
+                # SMA-10: the Stop button is the add-on going quiet, so a unit
+                # that hands back is given back; every other unit is zeroed.
+                await self.command_site_release()
             return {"auto": self.auto}
         if what in ("maint_start", "maint_abort") and unit is not None:
             # MAINT-11: the operator named the battery. A request with no unit
@@ -8055,6 +8250,21 @@ MAINT_CHARGING_W = 50.0
 EXIT_CONTROL_DIED = 70
 
 
+async def _bounded(awaitable, budget_s: float):
+    """SMA-10. `await awaitable`, but give up after `budget_s` and do NOT wait
+    for it to wind down. `asyncio.wait_for` waits for the cancelled task to
+    finish, so a driver that ignores its cancellation would hold the whole
+    shutdown; this abandons it. Raises `asyncio.TimeoutError` at the bound."""
+    task = asyncio.ensure_future(awaitable)
+    done, _ = await asyncio.wait({task}, timeout=budget_s)
+    if not done:
+        task.cancel()
+        # a result or error that arrives later has nobody to read it
+        task.add_done_callback(lambda t: t.cancelled() or t.exception())
+        raise asyncio.TimeoutError
+    return task.result()
+
+
 class ControlTaskDied(RuntimeError):
     """The control task ended while nothing had asked it to stop."""
 
@@ -8081,10 +8291,12 @@ def control_task_done(task: asyncio.Task, *, controller, stop: asyncio.Event,
     if stop.is_set() or controller.stopping:
         return          # the normal wind-down, or run_control()'s refusal path
     exc = None if task.cancelled() else task.exception()
-    _LOG.critical("Control stopped unexpectedly (%s), so every inverter is "
-                  "set to 0 W and the add-on exits with code %d.",
+    _LOG.critical("Control stopped unexpectedly (%s), so %s and the add-on "
+                  "exits with code %d.",
                   "cancelled" if task.cancelled() else
-                  (repr(exc) if exc else "returned"), EXIT_CONTROL_DIED,
+                  (repr(exc) if exc else "returned"),
+                  handback.task_died_state(handback.current()),
+                  EXIT_CONTROL_DIED,
                   exc_info=exc)
     died.append(exc)
     stop.set()

goodwe_controller/app/messages.py

@@ -12,6 +12,8 @@ import re
 from dataclasses import dataclass
 from datetime import datetime
 
+from . import handback
+
 # Severity (STYLE.md section 3). An ALARM may use up to three sentences so
 # that no action a person must take is lost; everything else gets one.
 ALARM, WARNING, INFO, RESOLVED = "alarm", "warning", "info", "resolved"
@@ -228,6 +230,19 @@ class Clamp:
     limit: str          # a key of LIMIT_WORDS
 
 
+def _shadow_so(held: str) -> str:
+    """"Shadow mode is on, so <held>." SMA-10: with a unit handed back, the
+    roster's own words say where each unit stays; otherwise `held`, as ever."""
+    moved = handback.shadow_state(handback.current(), "en")
+    return f"Shadow mode is on, so {moved or held}."
+
+
+def _shadow_keeps(held: str) -> str:
+    moved = handback.clause(handback.current(), "en", "at") \
+        if handback.active(handback.current()) else None
+    return moved or held
+
+
 def output_clamp(clamps, *, shadow: bool = False) -> Notice:
     """SAFETY-03: a computed command above the limit. A software fault.
 
@@ -238,7 +253,7 @@ def output_clamp(clamps, *, shadow: bool = False) -> Notice:
     fault = "This is a software fault, so please report it to your installer."
     if not clamps:
         cut = ("would have been cut back" if shadow else "was cut back")
-        state = ("Shadow mode is on, so every inverter stays at 0 W." if shadow
+        state = ((_shadow_so("every inverter stays at 0 W")) if shadow
                  else "Control is still running.")
         return Notice(ID_OUTPUT_CLAMP, ALARM, T_OUTPUT_CLAMP,
                       f"The add-on asked for more power than {RATING} allows "
@@ -250,11 +265,11 @@ def output_clamp(clamps, *, shadow: bool = False) -> Notice:
     if others:
         verb = "was" if len(others) == 1 else "were"
         state = (f"{names(others)} would have been cut too, and shadow mode "
-                 f"keeps every inverter at 0 W." if shadow else
+                 f"keeps {_shadow_keeps('every inverter at 0 W')}." if shadow else
                  f"{names(others)} {verb} cut too, and control is still "
                  f"running.")
     else:
-        state = ("Shadow mode is on, so the inverter stays at 0 W." if shadow
+        state = (_shadow_so("the inverter stays at 0 W") if shadow
                  else "Control is still running.")
     return Notice(ID_OUTPUT_CLAMP, ALARM, T_OUTPUT_CLAMP,
                   f"{who} add-on asked for {watts(c.asked_w)}, above "
@@ -576,6 +591,9 @@ def banner_running() -> str:
 
 
 def banner_stopped() -> str:
+    moved = handback.banner_stopped(handback.current())
+    if moved is not None:       # SMA-10: a unit is handed back, not held
+        return moved
     return Bi("Stopped — the inverters are set to 0 W",
               "Gestopt — de omvormers staan op 0 W")
 
@@ -601,6 +619,9 @@ def banner_shadow(latched: bool) -> str:
     mode. Each stop has its own red row below, which names it and says how it
     clears.
     """
+    moved = None if latched else handback.banner_shadow(handback.current())
+    if moved is not None:       # SMA-10: a unit is handed back, not held
+        return moved
     if latched:
         return Bi("Shadow mode: battery not controlled. A safety stop stays "
                   "on, see below.",
@@ -1367,6 +1388,8 @@ HINTS = {
     "setup_only": "In setup, nothing is sent to any inverter",
     "roster": "Inverter list read: {n} inverters",
     "maint_history": "Maintenance history did not move over cleanly",
+    "handed_back": "{unit}: handed back, the add-on writes nothing to it",
+    "hand_back_failed": "{unit}: could not be handed back, set to 0 W once, trying again",
     "stop_restored": "{unit}: an earlier safety stop is back, it stays at 0 W",
     "readings_late": "Home Assistant readings arrive late, control holds",
     "readings_back": "Home Assistant readings are on time again",
@@ -1470,6 +1493,10 @@ def hint(key: str, **kw) -> str:
         kw["w"] = watts(kw["w"])
     if "sw" in kw:
         kw["sw"] = signed_watts(kw["sw"])
+    if key == "shadow_on":      # SMA-10: a unit handed back is not at 0 W
+        moved = handback.hint_shadow_on(handback.current())
+        if moved is not None:
+            return moved
     return HINTS[key].format(**kw)
 
 

goodwe_controller/app/uitext.py

@@ -13,6 +13,11 @@ import os
 DIR = os.path.join(os.path.dirname(os.path.abspath(__file__)), "ui_text")
 LANGS = ("en", "nl")
 _CACHE: dict = {}
+# SMA-10. The sentences that move with the roster (handback.overlay): empty for
+# every GoodWe-only roster, and then `raw()` is the file as it always was.
+_IDLE: dict = {}
+_GEN = [0]
+_MERGED: dict = {}
 
 
 def lang_of(value) -> str:
@@ -21,14 +26,36 @@ def lang_of(value) -> str:
     return head if head in LANGS else "en"
 
 
-def raw(lang: str) -> dict:
-    """One language file as written, without the English fallback."""
+def _file(lang: str) -> dict:
     if lang not in _CACHE:
         with io.open(os.path.join(DIR, f"{lang}.json"), encoding="utf-8") as f:
             _CACHE[lang] = json.load(f)
     return _CACHE[lang]
 
 
+def set_idle(overlay: dict) -> None:
+    """SMA-10: the roster-built sentences, `{lang: nested dict}` (or {})."""
+    _IDLE.clear()
+    _IDLE.update(overlay or {})
+    _MERGED.clear()
+    _GEN[0] += 1
+
+
+def generation() -> int:
+    """Changes whenever `set_idle()` does, so a cache of words can tell."""
+    return _GEN[0]
+
+
+def raw(lang: str) -> dict:
+    """One language file as written, without the English fallback (and with the
+    roster's own sentences laid over it when a unit is handed back)."""
+    if lang not in _IDLE:
+        return _file(lang)
+    if lang not in _MERGED:
+        _MERGED[lang] = _merge(_file(lang), _IDLE[lang])
+    return _MERGED[lang]
+
+
 def _merge(base, over):
     if not (isinstance(base, dict) and isinstance(over, dict)):
         return copy.deepcopy(over)

goodwe_controller/app/web.py

@@ -442,7 +442,8 @@ def build_app(controller, selfcfg=None) -> web.Application:
         """Restart the add-on, at the operator's explicit request.
 
         ⚠️ THIS IS THE ONE ROUTE ON THIS SURFACE THAT COSTS ANYTHING. The
-        wind-down commands 0 W on every inverter (`Controller.shutdown()`), so
+        wind-down commands 0 W on every inverter, or hands a unit back when its
+        driver does (`Controller.shutdown()`, SMA-10), so
         the request must carry the intent token; a reload, a retry or a stray
         POST cannot spend a control interruption. It restarts THIS ADD-ON and
         nothing else: no setpoint is written from here, and a latched failsafe

goodwe_controller/config.yaml

@@ -1,5 +1,5 @@
 name: GoodWe RS485 Controller
-version: "0.20.1"
+version: "0.21.0"
 slug: goodwe_controller
 description: >-
   Drives a GoodWe ES/BP battery inverter over its RS485 EMS port by sending it a

goodwe_controller/test_messages.py

@@ -793,6 +793,7 @@ from datetime import datetime as _dt, timedelta as _td, timezone as _tz  # noqa:
 
 from app import clamp as _clamp, freshness as _fresh, peakguard as _pg   # noqa: E402
 from app import store as _store                                         # noqa: E402
+from app import handback                                                # noqa: E402
 from app.circulation import CirculationConfig, CirculationWatchdog      # noqa: E402
 from app.control import Tuning, compute                                 # noqa: E402
 from app.delivery import (DeliveryConfig, DeliveryWatchdog, UnitDelivery,  # noqa: E402
@@ -1058,6 +1059,12 @@ TEXT = {
     "main.py:messages.reason_code(inv.batt_fresh.reason)": _coded(_stale_texts),
     "main.py:rep.explain()": _migration_texts,
     "store.py:rep.explain()": _migration_texts,
+    # SMA-10: the control-task CRITICAL line's state, for a GoodWe-only roster
+    # (the sentence it always was) and a mixed one.
+    "main.py:handback.task_died_state(handback.current())": lambda: [
+        handback.task_died_state(()),
+        handback.task_died_state((handback.Unit("inverter-a"),
+                                  handback.Unit("inverter-b", True)))],
     "main.py:plan.words": _tariff_texts,
     # OPT-11 P2: why an MQTT command was ignored.
     "main.py:why": lambda: list(messages.PACK_REFUSED.values()),

goodwe_controller/test_safety137_last_write.py

@@ -0,0 +1,332 @@
+"""SAFETY-137: the 0 W of shutdown and of the Stop button is the last write every
+unit hears.  `python3 test_safety137_last_write.py`
+
+A cycle write already on its way (0.3-0.6 s, or hung) must not land after the
+0 W, for a GoodWe unit and for a fake unit that does not hand back, at N=1 and
+N=2, at shutdown and at Stop. The control cycle (and the heartbeat) issue no
+new write once shutdown has begun. The whole wind-down stays inside
+HAND_BACK_WORST_S (6 s) when a write hangs.
+
+Mutating a module this file grades? Read MUTATION.md first (purge __pycache__).
+The mutants this file was run against are listed at the end.
+"""
+
+import asyncio
+import sys
+import time
+from pathlib import Path
+
+HERE = Path(__file__).resolve().parent
+sys.path.insert(0, str(HERE))
+
+from app import main as M                                    # noqa: E402
+from app.drivers import Driver, Probe, REGISTRY             # noqa: E402
+from app.main import Controller                             # noqa: E402
+from app.store import DEFAULTS                              # noqa: E402
+
+fails = []
+
+
+def check(name, cond):
+    print(f"  {'ok  ' if cond else 'FAIL'} {name}")
+    if not cond:
+        fails.append(name)
+
+
+class PlainFake(Driver):
+    """A unit that does not hand back (so, like GoodWe, no release()). A write
+    of anything but 0 W takes `delay` s to land; every write is logged when it
+    LANDS (`landed`) and when it STARTS (`started`)."""
+    name = "plainfake"
+    writer_key = "host"
+    brand = "Fake"
+    hands_back = False
+    delay = 0.0
+
+    def __init__(self, host="", port=502, unit_id=1, rating=2000.0):
+        self.host, self.port, self.unit_id = host, port, unit_id
+        self.rating, self.power = rating, 0.0
+        self.landed, self.started = [], []
+
+    @classmethod
+    def from_entry(cls, entry):
+        return cls(entry.get("host", ""), entry.get("port", 502),
+                   entry.get("unit_id", 1))
+
+    @classmethod
+    def actuator_id_of(cls, entry):
+        host = str(entry.get("host") or "").strip()
+        return f"{host}:{entry.get('port', 502)}:{entry.get('unit_id', 1)}" \
+            if host else ""
+
+    def configured(self):
+        return bool(self.host)
+
+    def actuator_id(self):
+        return f"{self.host}:{self.port}:{self.unit_id}"
+
+    def soc_source(self):
+        return "fake-soc"
+
+    def batt_source(self):
+        return "fake-power"
+
+    async def limits(self):
+        return -self.rating, self.rating
+
+    async def read(self):
+        return 60.0, self.power, {}
+
+    async def write(self, w):
+        self.started.append((time.monotonic(), float(w)))
+        if w != 0 and self.delay:
+            await asyncio.sleep(self.delay)
+        self.landed.append((time.monotonic(), float(w)))
+        self.power = w
+        return True
+
+    async def probe(self):
+        return Probe(-self.rating, self.rating, 60.0, self.power, {})
+
+
+REGISTRY["plainfake"] = PlainFake
+
+
+class MemStore:
+    def __init__(self):
+        self.data = dict(DEFAULTS)
+
+    def set(self, k, v):
+        self.data[k] = v
+
+    def get_time(self, *a):
+        return None
+
+    def set_time(self, *a):
+        pass
+
+
+class Pub:
+    enabled = False
+
+    def publish(self, values):
+        pass
+
+    def close(self):
+        pass
+
+
+class SlowHass:
+    """Home Assistant for the GoodWe units. A set_number of anything but 0 W
+    takes `delay` s to land; the log gets the write when it lands."""
+
+    def __init__(self):
+        self.delay = 0.0
+        self.landed, self.started = [], []        # (t, entity, value)
+        self.numbers = {"sensor.grid": 3000.0, "sensor.soc_a": 50.0,
+                        "sensor.batt_a": 0.0, "sensor.soc_b": 50.0,
+                        "sensor.batt_b": 0.0}
+
+    async def number(self, entity, invert=False):
+        return self.numbers.get(entity)
+
+    async def limits(self, entity):
+        return (-3000.0, 3000.0, 1.0)
+
+    async def set_number(self, entity, value):
+        self.started.append((time.monotonic(), entity, value))
+        if value != 0 and self.delay:
+            await asyncio.sleep(self.delay)
+        self.landed.append((time.monotonic(), entity, value))
+        return True
+
+    async def state(self, entity):
+        return None
+
+    async def call(self, *a):
+        return True
+
+
+def gw(name, suffix):
+    return dict(name=name, setpoint_entity=f"number.sp_{suffix}",
+                soc_entity=f"sensor.soc_{suffix}",
+                batt_entity=f"sensor.batt_{suffix}", max_w=3000,
+                bms_soc_floor=10)
+
+
+def fk(name):
+    return dict(name=name, driver="plainfake", host="10.9.9.9", port=502,
+                unit_id=3, max_w=2000, bms_soc_floor=10)
+
+
+ROSTERS = {
+    "N=1 GoodWe": [gw("inverter-a", "a")],
+    "N=1 fake": [fk("inverter-a")],
+    "N=2 GoodWe+GoodWe": [gw("inverter-a", "a"), gw("inverter-b", "b")],
+    "N=2 GoodWe+fake": [gw("inverter-a", "a"), fk("inverter-b")],
+}
+
+
+def site(inverters, delay):
+    opts = dict(meter_source="off", meter_entity="sensor.grid", max_w=5000,
+                gain=0.6, slew_w=0, deadband_w=15, target_grid_w=0, step_w=10,
+                heartbeat_s=10, stale_input_s=15, shadow_mode="off",
+                inverters=inverters)
+    hass = SlowHass()
+    hass.delay = delay
+    c = Controller(opts, hass, MemStore(), Pub(), stop=asyncio.Event())
+    for inv in c.inverters:
+        inv.dev_min, inv.dev_max = -3000.0, 3000.0
+        if isinstance(inv.driver, PlainFake):
+            inv.driver.delay = delay
+    c.auto = True
+    return c, hass
+
+
+def per_unit(c, hass, kind="landed"):
+    """name -> [(t, value)] in the order the writes LANDED (or started)."""
+    out = {}
+    for inv in c.inverters:
+        d = inv.driver
+        if isinstance(d, PlainFake):
+            out[inv.name] = list(getattr(d, kind))
+        else:
+            ent = d.setpoint_entity
+            out[inv.name] = [(t, v) for t, e, v in getattr(hass, kind)
+                             if e == ent]
+    return out
+
+
+async def cycles(c, n=2):
+    for _ in range(n):
+        await c.read_inputs()
+        await c.cycle()
+
+
+async def in_flight(c):
+    """A cycle write on its way to every unit (what rig 5b had): the real
+    cycle, whose writes are authorised and take `delay` s to land."""
+    tasks = [asyncio.ensure_future(cycles(c, 1))]
+    await asyncio.sleep(0.1)
+    assert all(not t.done() for t in tasks)
+    return tasks
+
+
+async def finish(tasks):
+    for t in tasks:
+        t.cancel()
+    for t in tasks:
+        try:
+            await t
+        except BaseException:           # noqa: BLE001 - cancelled or timed out
+            pass
+
+
+def last_is_zero(c, hass):
+    got = per_unit(c, hass)
+    return all(w and w[-1][1] == 0.0 for w in got.values()), got
+
+
+def scenario(label, inverters, how, delay):
+    """how: 'shutdown' or 'stop'. Returns (seconds, ok, detail)."""
+    c, hass = site(inverters, delay)
+
+    async def go():
+        tasks = await in_flight(c)
+        t0 = time.monotonic()
+        if how == "shutdown":
+            await c.shutdown()
+        else:
+            await c.handle_action("auto_toggle")        # Stop
+        dt = time.monotonic() - t0
+        # let a write that is still on its way land, to see if it overtakes
+        await asyncio.sleep(0.8 if delay < 5 else 0.0)
+        await finish(tasks)
+        return dt
+
+    dt = asyncio.run(go())
+    ok, got = last_is_zero(c, hass)
+    n_sent = {n: len(w) for n, w in got.items()}
+    check(f"{label}: the cycle write was on its way at {how} (test sees it)",
+          all(len(w) >= 2 for w in per_unit(c, hass, "started").values()))
+    print(f"    {label}: {how}, delay {delay} s: {dt:.2f} s, "
+          f"landed per unit {n_sent}, last "
+          f"{ {n: (w[-1][1] if w else None) for n, w in got.items()} }")
+    return dt, ok, got
+
+
+print("SAFETY-137 - the 0 W is the last write")
+
+print("1. a slow write on its way (0.3 s, 0.6 s) when shutdown / Stop starts")
+for label, roster in ROSTERS.items():
+    for how in ("shutdown", "stop"):
+        for delay in (0.3, 0.6):
+            dt, ok, got = scenario(label, roster, how, delay)
+            check(f"{label}, {how}, {delay} s in flight: the last write per "
+                  f"unit is 0 W", ok)
+            check(f"{label}, {how}, {delay} s in flight: the slow write "
+                  f"landed first, then the 0 W (not dropped, not overtaken)",
+                  all(len(w) >= 2 and w[-2][1] != 0.0
+                      for w in got.values()))
+            check(f"{label}, {how}: took about the write, not the budget "
+                  f"({dt:.2f} s)", dt < delay + 1.0)
+
+print("2. a hung write on its way: the 0 W still reaches every unit, in time")
+for label, roster in ROSTERS.items():
+    for how in ("shutdown", "stop"):
+        dt, ok, got = scenario(label, roster, how, 3600.0)
+        check(f"{label}, {how}, hung write: 0 W landed on every unit and is "
+              f"its last write", ok)
+        check(f"{label}, {how}, hung write: inside HAND_BACK_WORST_S "
+              f"({dt:.2f} s <= {M.HAND_BACK_WORST_S:.0f} s)",
+              dt <= M.HAND_BACK_WORST_S)
+        check(f"{label}, {how}, hung write: the 0 W goes after the settle "
+              f"wait ({M.SETTLE_BUDGET_S:.0f} s), not after the write's own "
+              f"budget ({dt:.2f} s)", dt <= M.SETTLE_BUDGET_S + 0.5)
+
+print("3. no new write once shutdown has begun (cycle, heartbeat)")
+for label, roster in ROSTERS.items():
+    c, hass = site(roster, 0.4)
+
+    async def go3():
+        tasks = await in_flight(c)
+        s = asyncio.ensure_future(c.shutdown())
+        await asyncio.sleep(0)                      # shutdown has begun
+        begun = time.monotonic()
+        await cycles(c, 3)                          # would write: grid 3000 W
+        await c.send_heartbeats(10 ** 9, 10)        # every unit is due
+        await asyncio.wait_for(s, 10)
+        await asyncio.sleep(0.8)
+        await finish(tasks)
+        return begun
+
+    begun = asyncio.run(go3())
+    starts = per_unit(c, hass, "started")
+    late = {n: [v for t, v in w if t >= begun and v != 0.0]
+            for n, w in starts.items()}
+    check(f"{label}: no non-zero write started after shutdown began "
+          f"({late})", all(not v for v in late.values()))
+    ok, got = last_is_zero(c, hass)
+    check(f"{label}: and the last write per unit is 0 W", ok)
+    # sanity: the same cycles DO write before shutdown
+    c2, hass2 = site(roster, 0.0)
+    asyncio.run(cycles(c2, 3))
+    before = per_unit(c2, hass2, "started")
+    check(f"{label}: control, same cycles before shutdown, write non-zero "
+          f"(the test can see a write)",
+          all(any(v != 0.0 for _t, v in w) for w in before.values()))
+
+print()
+if fails:
+    print(f"FAILED {len(fails)}:")
+    for f in fails:
+        print("  -", f)
+    sys.exit(1)
+print("all ok")
+
+# MUTANTS this file was run against (each must turn it red):
+#  (a) _await_inflight does nothing (no wait for in-flight writes), GoodWe too
+#  (b) the `elif self.stopping: return` gate removed (cycle not stopped)
+#  (c) `last=True` not passed by command_site_release (Stop/shutdown 0 W is a
+#      plain write)
+#  (d) the wait unbounded (no timeout): red on the settle-bound check