1. /json client IP (codex #1, Medium): HandleJson now validates
c.ClientIP() and returns 400 on a malformed value instead of letting
Query fail into a 500. HandleIpInfo gained a selfLookup flag so a valid
but DB-absent self-IP preserves the 9d07639 graceful 200 {"ip": ip}
default (private/loopback addresses are never in a public GeoIP DB),
while the explicit /:ip route still returns 404 on not-found.
2. updated_at=0 on initial load (codex #2, Low): stampDbUpdatedAt() now
records the canonical mmdb's mtime both on initial load (existing
files) and after each successful update, so /metrics never reports 0
while serving real data.
3. Merge corruption -> permanent outage: mmdbmeld.WriteMMDB truncates the
canonical mmdb before writing; a failed merge previously left it empty
and the saved etag made the next daily run 304-skip the retry, so a
restart failed to open the file and the service went 503 permanently.
fetchDbs now backs up the canonical file before merge, restores it on
merge/reload failure, and drops the etags so the next run retries.
4. Temp-file leaks: Reload removes the temp clone and restores d.dbFile
when reader.Open fails (it previously assigned d.dbFile before Open);
cloneDBFile removes the temp on a failed copy.
Verified: go build, go vet, gofmt -l, go test -race ./... all pass.
Co-Authored-By: Claude <noreply@anthropic.com>