Capacity is a human summary of what the machine has ("8 vCPU / 32G", "1× GB10"), up to 256 characters. Prose for a card — Spec is the same thing in a form a scheduler can read, and nothing derives one from the other.
CreatedAt is when the machine was first registered, RFC 3339 in UTC. A re-link refreshes the row and leaves this alone, so it dates the machine and not the connection.
Host is the hostname sessions on this machine report, and it is a JOIN KEY, not a label: a session naming this host counts against the load below even when it names no target id, and a re-link of the same (org, host, owner) refreshes this row instead of creating a second. Empty means the machine is addressable only by ID.
ID is the machine's handle, minted as "tgt_" + 32 hex characters. It is what a session records to say it ran here, and what every later patch, claim or delete addresses.
Label is the name a person gave the machine ("workshop"), up to 128 characters. Required at register, free text, and the only field here meant for reading rather than matching.
Metrics is what the machine was DOING at its last heartbeat — loadavg, memory, accelerator utilization. Absent when it has never beaten. It is a SNAPSHOT: the series over time lives in the fleet samples, not here.
MetricsAt is when that heartbeat was recorded, RFC 3339 in UTC, and the SERVER stamps it — a client cannot backdate or forge the staleness clock. Absent means never beaten, which is exactly the case where Status is taken at its word.
Spec is what the machine IS — os, arch, cores, RAM, accelerators — the static half, changed only when something reports it again. Absent when nothing has ever been reported, and a scheduler reads absence as "cannot satisfy a floor" rather than as "no limits".
Status is the EFFECTIVE liveness — online | offline | draining — not the stored one. offline and draining are operator INTENT and are reported as they stand; online is checked against the heartbeat, and a machine that has beaten before but not in the last 90 seconds reports offline whatever its row says. A target that has NEVER beaten keeps its stored status, because a hand-registered destination has no fact to check.
