Active observers vanish as nodes after retention.nodeDays without an advert; observer link dead-ends on 'Node not found' #199

Summary

An observer that is online can vanish as a node.

• The node row is moved to inactive_nodes after retention.nodeDays without an advert, even though the same device is actively uploading as an observer.
• The Observers page still lists it as online. Its "View node detail" link (public/observer-detail.js around line 84) then opens #/nodes/<pubkey>, which shows "Node not found" (public/nodes.js around line 1136).
• The node is also missing from the map with every status filter.

Evidence

Production, read-only, 2026-10-04, reported by users:

• Observer: a repeater observer in one region. Its observers.last_seen is current (2026-10-04T04:23Z), and it was first seen 2026-09-11.
• nodes: no row for its pubkey. /api/nodes/<pubkey> returns 404.
• inactive_nodes: has the row, with last_seen 2026-09-24T15:35Z.
• Adverts: its last advert in transmissions is from 2026-09-23T06:33Z.
• Config: retention.nodeDays is 7. MoveStaleNodes (cmd/ingestor/db.go around line 1900, called from main.go at start-up and daily) moves every node whose last_seen < now - nodeDays. last_seen is updated only by adverts and direct upserts. Observer activity does not count.

This is not a regression. The behaviour predates v0.2.0.

Why adverts can be missing. A node never receives its own transmissions, so its adverts must be heard by another observer. The firmware's flood.advert.interval can be set from 3 to 168 hours, with a default of 12 hours for repeaters. At 168 hours, a node with nodeDays: 7 flickers in and out of nodes. A badly placed node may also simply not reach any other observer for a week.

Proposed changes

A. Ingestor: do not retire active observers. In MoveStaleNodes, exclude nodes whose pubkey matches an observer seen within nodeDays. Observer IDs are upper-case pubkeys and node keys are lower-case, so the comparison must normalise case.

• When the observer goes quiet, the node is retired as before.
• This needs a test: an active observer whose node has an old last_seen stays in nodes, and an inactive one is moved.
• last_seen must not be faked. The node page should still show when the last advert was heard.

B. UI: do not dead-end on "Node not found".

• Option 1: when the node is missing but present in inactive_nodes, the node page says so, e.g. "No advert heard since ; this device is inactive", and shows the inactive row's name and role.
• Option 2: at minimum, the observer-detail page does not offer "View node detail" for a pubkey that has no nodes row, or it explains why.

cmd/server/identity_visibility.go already reads inactive_nodes, so there is a read-only precedent in the server.

Acceptance criteria

• An online observer whose last advert is older than nodeDays stays visible as a node, on the map and on the node page (test in cmd/ingestor).
• A node that is in neither nodes nor the active observer set is retired as before (test).
• From the Observers page, a device without a nodes row never dead-ends on a bare "Node not found". Either the page explains the state or the link is hidden (unit or E2E test).
• No new per-item API calls, and the server stays read-only.

Out of scope

• Changing retention.nodeDays on any instance; that is an operational decision.
• The map status filter. It defaults to "All" and only persists the user's own last choice in localStorage (meshcore-map-status-filter).