Summary

Adds an opt-in reportOffline flag (default: false) that marks bulbs as "Not Responding" in HomeKit once they miss offlineThreshold consecutive getPilot replies, rather than silently replaying the last known cached state. Reachability is cleared on any successful getPilot reply or any registration / getSystemConfig response from the same MAC, so bulbs that come back online recover immediately.

Leaves existing behaviour unchanged when the flag is left at its default.

Background

Today, when a bulb stops responding to UDP getPilot requests, src/accessories/WizLight/pilot.ts:152-158 (and the same pattern in WizSocket/pilot.ts:72-78) returns the cached pilot:

const timeout = setTimeout(() => {
  if (device.mac in cachedPilot) {
    onDone(null, cachedPilot[device.mac]);   // replays stale state
  } else {
    onDone(new Error("No response within 1s"), undefined as any);
  }
}, 1000);

The original rationale (#48, 2021) was that HAP couldn't surface "Not Responding" at the time — but HomeKit does now honour an Error returned from a characteristic get callback by showing the tile as Not Responding, which is what users expect. The error plumbing that #41 already threaded through util/network.ts makes surfacing this trivial.

What this changes

• New src/util/reachability.ts — tiny pure module tracking consecutive miss counts per MAC. recordHit / recordMiss / isOffline(mac, threshold).
• WizLight/pilot.ts + WizSocket/pilot.ts: on getPilot timeout, record a miss. If reportOffline is on and the miss count hits offlineThreshold, surface the error up the existing onError callback instead of returning cached state. On any successful reply, clear the miss count.
• util/network.ts: on any incoming registration or getSystemConfig reply, clear the miss count for that MAC (bulb is demonstrably alive).
• wiz.ts::initRefreshInterval: when refreshInterval > 0, also re-broadcast discovery on each tick so bulbs returning to the network (or acquiring a new DHCP lease) re-announce themselves — otherwise device.ip can stay stale indefinitely. Refresh-loop failures log at debug instead of error to avoid spamming the log once per tick per offline bulb (matches the convention established by Change log level of pings to debug #141).
• config.schema.json + README.md: new reportOffline: boolean (default false) and offlineThreshold: integer (default 3).

Pairs naturally with the refreshInterval polling added in #128 — background pings detect unreachable bulbs without waiting for HomeKit to read them.

Log hygiene

Because discovery now re-broadcasts every tick, sendDiscoveryBroadcast was also downgraded to debug. Similarly, tryAddDevice's "Updating accessory:" line now logs at info only when the display name actually changed; otherwise debug. Without these, a typical 7-bulb / 30s-refresh setup would produce ~22 info-level lines per minute from our changes alone. Same rationale as #141.

Bundled defensive fixes in the same code region

Two narrow undefined-handling fixes in pilot.ts that live in the exact lines this PR touches and address recurring issues:

• Filter undefined fields from the getPilot reply before merging into cachedPilot. Firmware replies for certain scenes (notably sceneId: 14, "nightlight") omit dimming entirely, and a naked spread clobbered the state-based default with undefined, producing NaN Brightness in HomeKit. Addresses NaN error from brightness #96, NaN Error Isolated to "sceneId":14 #101 (MoTechnicalities' root-cause), brightness warning #143, Characteristic Warning for Wiz Plugin #159.
• pilotToColor() falls back to a neutral-white reading when passed an empty cache entry. Prevents the "Cannot read properties of undefined (reading 'temp')" crash when a temperature / color set handler runs after a timeout wiped the cache. Addresses "Unhandled error thrown inside write handler for characteristic: Cannot read properties of undefined (reading 'temp')" when controlling Wiz bulb #145.

Issues addressed

Primary (silent-stale-state pattern): #135, #140, #105, #87, #97, #160, #167

Bundled (NaN / undefined-temp crashes in the same code region): #96, #101, #143, #145, #159

Compatibility

• Default behaviour is unchanged — the flag is opt-in.
• No schema changes that affect existing config.
• No new dependencies.
• Error plumbing reuses the signature introduced by Improve network response #41.
• Diff: +139 / -10 across 8 files.

Test plan

• npm run build clean (no TS errors on Node 25).
• Deployed to a Homebridge container with 6 real Wiz bulbs (4 online, 2 on a cut-power wall switch). reportOffline: true, refreshInterval: 30.
• tcpdump across a 3-minute window: online bulbs received broadcasts every 30s and replied every 30s; offline bulbs received broadcasts but never replied.
• Online bulbs remain reachable in HomeKit with no log output; offline bulbs surface as "Not Responding" within offlineThreshold × refreshInterval (default 90s); powering them back on restores state on the next refresh tick.
• With reportOffline: false (default), behaviour is byte-for-byte the same as before — confirmed by diffing log output against pre-PR build.

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