[GreenGrassBlueOcean]

Summary

Resolves #619: Handle BTicino phase-cut dimmer unloaded / open-circuit state (*1*19*<WHERE>##).

Physical modular phase-cut dimmers (e.g. BTicino F414) require a minimum closed load circuit for AC zero-crossing detection. When no load is attached or a lamp filament is blown, the dimmer enters an unloaded state and emits *1*19*<WHERE>##.

Previously, this resulted in:

1. Dimmers becoming permanently stuck in the UI as ON at 1% brightness when operated.
2. Dimmer entities being auto-discovered as non-dimmable switches (ColorMode.ONOFF).
3. Persistent unmapped_device_status repair issues being raised for unused cabinet channels.

Details & Behavior

1. Light Entity (custom_components/myhome/light.py):
   • Treats WHAT 19 as _attr_is_on = False, preventing the entity from remaining stuck ON at 1%.
   • Exposes no_load: true in extra_state_attributes while unloaded.
   • Logs state transitions to no_load once at INFO level (subsequent recurring unloaded frames log at DEBUG), ensuring blown lamps or disconnected loads are visible in standard logs without spam.
   • Normal OFF commands (*1*0*<WHERE>##) preserve no_load: true (turning off an unloaded channel does not imply a load was connected).
   • no_load is cleared and an INFO message logged when an active load reconnects (positive is_on = True or level frame arrives).
   • Automatically promotes existing entities to ColorMode.BRIGHTNESS on receiving WHAT 19 (respecting lock_features).
   • Automatically discovers unloaded dimmers as dimmable = True in build() when first seen via WHAT 19.
2. Device Health & Diagnostics (custom_components/myhome/device_health.py, docs/diagnostics/repair-issues.md):
   • Added 19 to RECOGNIZED_STATUSES in device_health.py (keeping DOCUMENTED_EVENTS strictly for ZigBee spec events {32, 34, 39}).
   • Receiving WHAT 19 clears any prior unmapped_status fault on that address without raising new repair issues.
   • Updated diagnostic documentation in docs/diagnostics/repair-issues.md.
3. Trace Fixtures & Conformance (tests/fixtures/traces/issue_619/, README.md, docs/trace-availability.md):
   • Committed authentic physical F453AV & F414 bus trace contributed by @nce2704 in Investigate lighting WHAT 19 status frames from BTicino F414 modular dimmers #619 (myhome_trace_F453AV_all_2026-10-04T08-28-13.json) with README documentation.
   • Added trace replay test suite in tests/test_issue_619_dimmer_trace.py verifying discrete dimming levels 2..7 with 35 W load, turn off transitions, and unloaded channel WHAT 19 handling.
   • Synchronized trace availability matrix across README.md and documentation.
4. Unit Tests:
   • tests/test_component_light.py: Unit tests for WHAT 19 no-load behavior, stuck-on prevention, async_turn_on() UI execution, level recovery, OFF command preservation of no_load, state transition logging, and dimmable discovery.
   • tests/test_device_health.py: Verified WHAT 19 clears unmapped status faults and raises no repair issues.
   • tests/test_device_health_corpus.py: Replay suite tests verifying DOCUMENTED_EVENTS and RECOGNIZED_STATUSES.

Verification

• WSL Python 3.14 / HA Core 2026.9.2: Full test suite passed (218 component/health/trace tests passed).

• Ruff Linting: 0 violations across custom_components, tests, and scripts.

• Architectural Standards: All 22 checks passed via scripts/verify_ha_standards.py.

• V2 Architecture: New entities implement handle_event() and do not manually subscribe via async_dispatcher_connect.

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