REMINDER: Restoring pgnInstances: Active Instance Tracking via FullSignalK (TypeBox & Source UX)

[dirkwa]

Restoring pgnInstances: Active Instance Tracking via FullSignalK

Context

The source-priority-ux branch originally built on top of the TypeBox PR (#2325), which migrated FullSignalK from @signalk/signalk-schema (npm package) into @signalk/server-api as TypeScript source. This allowed us to extend handleNmea2000Source with continuous pgnInstances tracking.

When we rebased source-priority-ux onto master without TypeBox, we lost this capability because FullSignalK is back in @signalk/signalk-schema and cannot be modified.

What was lost

In the TypeBox version, packages/server-api/src/fullsignalk.ts had this addition inside handleNmea2000Source:

// Accumulate data instances per PGN for conflict detection.
if (source.instance !== undefined) {
  const pi = (existing.n2k.pgnInstances ??= {} as Record<string, number[]>)
  const pgn = String(source.pgn)
  const arr = (pi[pgn] ??= [])
  const inst = Number(source.instance)
  if (!isNaN(inst) && !arr.includes(inst)) {
    arr.push(inst)
  }
}

This ran on every N2K delta, continuously building up which data instances each device uses per PGN. The result was available via /signalk/v1/api/sources in the pgnInstances field of each device's n2k object.

Current fallback

sourceLabels.ts already has a fallback path:

const aInst = a.pgnInstances?.[pgn] ?? pgnDataInstances?.[a.src ?? '']?.[pgn]

The pgnDataInstances comes from n2k-discovery.ts, which listens to the N2K bus for a fixed duration when the user clicks "Discover" in the Source Discovery UI. This is a point-in-time snapshot, not continuous.

What to restore when TypeBox merges

When the TypeBox PR merges and FullSignalK is back in server-api as TypeScript:

1. Re-add the pgnInstances tracking block to handleNmea2000Source in packages/server-api/src/fullsignalk.ts (code above)

2. The N2kDeviceInfo interface in packages/server-admin-ui/src/utils/sourceLabels.ts already has the pgnInstances field — no change needed

3. The sourceLabels.ts conflict detection already prefers pgnInstances over pgnDataInstances — no change needed

4. The Sources REST API (/signalk/v1/api/sources) will automatically include pgnInstances because it returns FullSignalK.retrieve().sources

In short: just restore the one code block in handleNmea2000Source and everything else reconnects automatically.

[dirkwa]

Update:

I noticed that without that a instance change is a nightmare. Passive detection is here not enough. Working on a solution.