getHealth: expose latest ledger close time (latestLedgerCloseTime)

[felixl256]

Problem

getHealth returns latestLedger (the sequence of the most recently ingested ledger) but not the time at which that ledger closed.

To assess ledger freshness today, a client has to additionally call getLatestLedger, which always returns the full headerXdr + metadataXdr of the ledger (several MB on active ledgers, since metadataXdr is the entire LedgerCloseMeta). That is far too heavy for a lightweight health/monitoring probe that only needs a timestamp.

Proposal

Add a latestLedgerCloseTime field (unix timestamp, in seconds) to the getHealth response.

• The value is already loaded inside the handler — it's used for the existing max-healthy-ledger-latency check (time.Unix(ledgerRange.LastLedger.CloseTime, 0)), so there is no additional cost.
• Naming and format mirror the existing top-level latestLedgerCloseTime field already present in the getLedgers response (plain int64 unix seconds).
• Additive and backward-compatible (existing clients ignore the new field).

Use case

Health/monitoring tooling (e.g. load balancers, node-status pollers) can compute "time since last ledger" directly from the cheap getHealth endpoint, instead of polling getLatestLedger and transferring multi-MB ledger metadata on every cycle.

Implementation

• protocols/rpc: Add LatestLedgerCloseTime to GetHealthResponse go-stellar-sdk#5958 — adds LatestLedgerCloseTime to GetHealthResponse
• getHealth: return latestLedgerCloseTime in response #797 — populates the field in the getHealth handler