## Summary
Closes#871
The `/api/packets` endpoint could return packets with `null` hash or
timestamp fields. This was caused by legacy data in SQLite (rows with
empty `hash` or `NULL`/empty `first_seen`) predating the ingestor's
existing validation guard (`if hash == "" { return false, nil }` at
`cmd/ingestor/db.go:610`).
## Root Cause
`cmd/server/store.go` `filterPackets()` had no data-integrity guard.
Legacy rows with empty `hash` or `first_seen` were loaded into the
in-memory store and returned verbatim. The `strOrNil("")` helper then
serialized these as JSON `null`.
## Fix
Added a data-integrity predicate at the top of `filterPackets`'s scan
callback (`cmd/server/store.go:2278`):
```go
if tx.Hash == "" || tx.FirstSeen == "" {
return false
}
```
This filters bad legacy rows at query time. The write path (ingestor)
already rejects empty hashes, so no new bad data enters.
## TDD Evidence
- **Red commit:** `15774c3` — test `TestIssue871_NoNullHashOrTimestamp`
asserts no packet in API response has null/empty hash or timestamp
- **Green commit:** `281fd6f` — adds the filter guard, test passes
## Testing
- `go test ./...` in `cmd/server` passes (full suite)
- Client-side defensive filter from PR #868 remains as defense-in-depth
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Co-authored-by: you <you@example.com>
Kpa-clawbot