docs: publish Preview 19 dogfood evidence

Export the reviewed allowlisted snapshot from private source commit 05928cebd01b586cf9e9d4b8c8537a7605a6068c. This records the exact candidate, bounded capacity result, stateful migration scratch requirement, authenticated batch identity proof, and immediate live acceptance evidence.

AI-Assisted: OpenAI Codex
Signed-off-by: Cole Speelman <crspeelman@gmail.com>

internal/nativeprotocol/headers_test.go

@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package nativeprotocol
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+	"time"
+
+	"gamertan.com/observatory/internal/model"
+)
+
+func TestEnvelopeHeadersRoundTripAndRejectAmbiguity(t *testing.T) {
+	now := time.Date(2026, 8, 18, 20, 0, 0, 0, time.UTC)
+	batch := model.Batch{Version: model.BatchVersion, SourceID: "source", StreamID: "logs", Sequence: 7, ObservedAt: now, Signal: model.SignalLogs, Records: []model.Observation{{Timestamp: now.Add(-time.Second), Name: "first"}, {Timestamp: now, Name: "last"}}}
+	body, err := json.Marshal(batch)
+	if err != nil {
+		t.Fatal(err)
+	}
+	envelope, err := batch.Envelope(body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	header := make(http.Header)
+	SetHeaders(header, envelope)
+	parsed, err := ParseHeaders(header, 1<<20)
+	if err != nil || parsed != envelope {
+		t.Fatalf("parsed=%+v err=%v", parsed, err)
+	}
+	header.Add(SequenceHeader, "8")
+	if _, err = ParseHeaders(header, 1<<20); err == nil {
+		t.Fatal("duplicate security-relevant header was accepted")
+	}
+}
+
+func FuzzParseEnvelopeHeaders(f *testing.F) {
+	f.Add("1", "logs", "1", "logs", "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb", "1", "100", "2026-08-18T20:00:00Z", "2026-08-18T20:00:00Z")
+	f.Fuzz(func(t *testing.T, version, stream, sequence, signal, wire, batch, count, size, first, last string) {
+		header := make(http.Header)
+		for name, value := range map[string]string{VersionHeader: version, StreamHeader: stream, SequenceHeader: sequence, SignalHeader: signal, WireDigestHeader: wire, BatchDigestHeader: batch, RecordCountHeader: count, EncodedBytesHeader: size, FirstObservedHeader: first, LastObservedHeader: last} {
+			header.Set(name, value)
+		}
+		_, _ = ParseHeaders(header, 32<<20)
+	})
+}