Keep device runtime state out of PostgreSQL

[yellowman]

Makes the devices table inventory/configuration-only and keeps poll-derived runtime state in memory.

Runtime state

• Removes poller writes of device status/status_reason for Wave, LTU/AirMAX, MAC mismatch, child propagation, association loss, and firmware upgrade runtime state.
• API no longer reads devices.status/status_reason. With no live stats after restart, status is intentionally unknown until a fresh poll.
• Reports derive status from the in-memory stats store rather than persisted device rows.
• MAC replacement relies on the durable device_identity_mismatches record rather than status_reason.

Last available

• Keeps last_seen as the one polling-derived durable marker.
• Persists it on an hourly wall-clock ticker, not per poll cycle.
• Uses one batch UPDATE with each device's actual in-memory LastSeen timestamp; rows are written at most roughly hourly and only when the in-memory timestamp is newer.
• Live API responses still expose the newer in-memory LastSeen while the process is running.

STA write amplification

• Child status propagation and association loss are memory/WebSocket-only.
• Stable existing STAs no longer receive a DB UPDATE on every AP peer poll.
• The hot existing-STA update is guarded by IS DISTINCT FROM checks so only real inventory changes write.
• New STA creation records inventory and initial last_seen, without persisted runtime status.

Other write reduction

• AirMAX GPS coordinates are treated as inventory: fill them if missing rather than rewriting on small GPS jitter.
• Explicit Add Device may stamp last_seen as part of the inventory transaction, but no longer persists status.

Legacy status/status_reason columns remain for schema compatibility but are documented as unused by the poller/API. Job, alert, audit, and mismatch records remain durable by design.

---

Note

Overview
Treats devices as durable inventory only and stops using PostgreSQL for poll-derived runtime state (online/offline, reasons, upgrading). After a restart, APIs and bulk ops report unknown until the in-memory stats store is populated—no fallback to stale devices.status.

Poller and children: Removes per-poll (and per-transition) UPDATE devices for status/reason across Wave, AirMAX/LTU, MAC mismatch, parent/child propagation, and missing STA association. Child updates SELECT identity from DB and push state via the stats store + WebSocket only. markMissingSTAsOffline uses SetStatusByMACChanged so WebSocket fires only when status/reason actually change.

last_seen: Replaces ~10-minute batch status/last_seen sync with an hourly syncLastSeenToDB that batch-updates each MAC’s in-memory timestamp (with skip logic for recent DB writes). Add/upsert paths no longer set status on insert/update; STA hot paths add IS DISTINCT FROM guards to avoid write amplification.

API/reports/firmware: List/get devices overlay status, reason, and fresher last_seen from live stats; reports use reportLiveStatus. Firmware jobs no longer set devices.status = 'upgrading'. Learn MAC keys off device_identity_mismatches instead of status_reason. AirMAX GPS is fill-once inventory (COALESCE); SPEC documents the pattern.

^{Reviewed by Cursor Bugbot for commit f2b5383. Bugbot is set up for automated code reviews on this repo. Configure here.}

Follow-up review fixes

• Missing/disconnected STAs now broadcast only when live status or status reason actually changes; repeated AP polls do not emit identical offline updates.
• Bulk upgrade dry-run no longer reads or falls back to devices.status; a device with no live stats is ineligible until freshly polled.
• Hourly last_seen persistence is chunked at 2,000 rows (4,000 bind parameters) per statement and binds Go timestamps as timestamptz.
• Removed the now-unused OnlineStatusBatch helper.
• Added a unit test covering repeated status/reason suppression and reason-only changes.
• SPEC documents AirMAX poller GPS as fill-once durable inventory with live in-memory overlay.

Validation

CI run 35412981298 is green on head f2b5383d43dea1faa0446cb2b089065b2c6deb0e:

• Go tests: passed
• Server build: passed
• JavaScript syntax: passed

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