KNX: `sync_state: false` rejected on 2026.9 for light/cover/climate — 47 entities not set up, unfixable via panel

### The problem

**The problem**

After upgrading 2026.8.3 → 2026.9.0 and again → 2026.9.1, 47 of my 88
UI-created KNX entities are no longer set up. Repair issues "Invalid KNX
entity configuration" are raised for light, cover and climate.

The correlation with `sync_state` in `.storage/knx/config_store.json`
is exact:

| platform | sync_state: false | true / string | not set up |
|---------------|-------------------|--------------------|------------|
| cover | 27 | 0 | 27 (all) |
| climate | 13 | 0 | 13 (all) |
| light | 7 | 33 | 7 |
| switch | 0 | 3 + 1 ("expire 2") | 0 |
| binary_sensor | 2 | 2 | 0 (!) |

Confirmed by editing the store: setting `sync_state: true` on exactly
those 47 entities makes all of them load again on 2026.9.1, with no
other change. So `sync_state: false` is the trigger.

Note binary_sensor: two entities have `sync_state: false` and are NOT
affected. The stricter validation appears to apply only to light,
cover and climate.

`sync_state: false` is a valid, documented setting, and it was written
by the KNX panel itself.

### What version of Home Assistant Core has the issue?

2026.9.1

### What was the last working version of Home Assistant Core?

2026.8.3

### What type of installation are you running?

Home Assistant OS

### Integration causing the issue

KNX

### Link to integration documentation on our website

https://www.home-assistant.io/integrations/knx

### Diagnostics information

_No response_

### Example YAML snippet

```yaml

```

### Anything in the logs that might be useful for us?

```txt
2026-09-07 17:35:27.163 ERROR (MainThread) [homeassistant.components.knx.repairs] Invalid KNX light configuration in storage. These entities were not set up: knx_es_01KFMXPD8TQBJYAT1CG9J644QZ, knx_es_01KFNEAZMVV1VT5349K86QNJZ1, knx_es_01KFNFZ2P2DS79ZBF01NNQJKA0, knx_es_01KFNG6HQGKXPY2SGBZXJ2XZ2N, knx_es_01KFNRKZ7Y9RGKRZZRV175P7XF, knx_es_01KFNRQMT1B1GC4QWNJZV0K11G, knx_es_01KFP4KEZ80WXQY216W0VJP6TR

2026-09-07 17:35:27.158 ERROR (MainThread) [homeassistant.components.knx.repairs] Invalid KNX climate configuration in storage. These entities were not set up: knx_es_01KJ2P9XMC7NGKGTT77AJDZS5G, knx_es_01KJ3G8QNDFYQPM01JGSGSG3Q1, knx_es_01KJ3HDV1453T6CY9V2241JDHS, knx_es_01KJ3HMT294M3JPMJQ2X9B9ERN, knx_es_01KJ3JWDYPFX3Z2727WFQFAYV9, knx_es_01KJHEEEWCTSSWY32GBCTVP52F, knx_es_01KJHEJCY6F1EK7ESTBTF818NM, knx_es_01KJHEN0B46BS6YHHSQC91WJ1W, knx_es_01KJTR0Q61PPJP2V67GWGXE071, knx_es_01KJTR234V9PCQ1F6ZGMVZJJEH, knx_es_01KJTR6E46EM7SYP5K4E2KXGSC, knx_es_01KJTR8035AGWJV1F8K7VEFMZN, knx_es_01KJTRD6XXVJMJJPDBK0WQHTM5

(the cover line is identical in form, listing 27 IDs — omitted for brevity)

These three ERROR lines are the only KNX output related to the failure.
No field name, no validation reason, and no other KNX error is logged
at ERROR level. Enabling debug logging for homeassistant.components.knx
would presumably reveal the offending key, but the ERROR message alone
gives the user nothing actionable — especially since the listed
knx_es_* IDs cannot be resolved to entity names in the UI, and the
entities themselves are not shown in the KNX panel.

For reference, the startup that followed after setting sync_state: true
on those 47 entities produced no knx.repairs errors at all, and instead:

2026-09-07 17:40:35.665 WARNING (MainThread) [xknx.log] Error: KNX bus did not respond in time (2.0 secs) to GroupValueRead request for: 31/1793
2026-09-07 17:40:35.665 WARNING (MainThread) [xknx.log] Could not sync group address '31/1793' (Rollo zentral - Position)
2026-09-07 17:41:20.328 WARNING (MainThread) [xknx.log] Could not sync group address '6/22' (Licht Spots Büro Christian - Brightness)
2026-09-07 17:41:22.329 WARNING (MainThread) [xknx.log] Could not sync group address '10/15' (KNX Garagentor Kabel - State)

47 of 47 read requests timed out over ~47 seconds, after which the KNX
IP interface stopped forwarding telegrams.
```

### Additional information

**Why the suggested remedy does not work**

1. The repair issue says "Correct or delete them", but entities that
were not set up do not appear in the KNX panel at all, so there is
no way to correct them through the UI. The only route left is
hand-editing `.storage`.

2. Setting `sync_state: true` is not a safe fallback for every
installation. On my system none of the actuators answer
GroupValueRead (47 of 47 requests time out, across unrelated
address ranges). With the 47 entities restored to `true`, startup
issued 47 reads over ~47 seconds and my KNX IP interface
(Weinzierl 752) stopped forwarding telegrams entirely and needed a
restart. `sync_state: false` was a deliberate setting on my system,
not leftover data.

3. The global KNX option `state_updater: false` does NOT suppress this
— it was already `false` throughout, and the per-entity
`sync_state: true` still triggered the reads. So there is no
integration-level escape hatch.

Together this means: on 2026.9 the entities are dropped, cannot be
fixed in the UI, and the only value the validator accepts can take the
KNX interface down.

**What you expected to happen**

`sync_state: false` keeps being accepted for light, cover and climate,
as it still is for binary_sensor.

**Storage versions**

knx/config_store: version 2, minor_version 4
core.entity_registry: version 1, minor_version 23
core.device_registry: version 3, minor_version 2

**Additional information**

- The store is otherwise clean: no `device_class` keys in the `entity`
block (so this is not #181299), no dangling or deleted device
references, config store and entity registry match 1:1.
- Rolling back to 2026.8.3 restores all 88 entities.
- The repair issue and the ERROR log line only list the opaque
`knx_es_*` storage IDs, not the offending field or the reason. The
actual validation error is not logged at ERROR level, which made
this take several hours to pin down. Logging the failing key would
help a lot.

**Version**: 2026.9.1 (also 2026.9.0)
**Installation type**: Home Assistant OS
**Integration**: knx
**Connection**: routing, multicast 224.0.23.12, IA 0.0.240