Freeze the Go implementation as a test-only oracle, with vectors

oracle/go is the Go code at 4c1507c, moved unchanged, plus test-only
generators that record what it computes. tests/vectors holds the
deterministic crypto/store vectors and synthetic fixtures they produce.

Co-Authored-By: Claude <noreply@anthropic.com>

oracle/go/internal/format/limits_test.go

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package format
+
+import (
+	"bufio"
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestStanzaReaderRejectsOversizedStanza(t *testing.T) {
+	var input bytes.Buffer
+	input.WriteString("-> test ")
+	input.WriteString(strings.Repeat("a", MaxStanzaSize))
+	input.WriteString("\n\n")
+
+	sr := NewStanzaReader(bufio.NewReader(&input))
+	if _, err := sr.ReadStanza(); err == nil {
+		t.Fatal("ReadStanza accepted an oversized stanza")
+	} else if !strings.Contains(err.Error(), "stanza exceeds") {
+		t.Fatalf("ReadStanza error = %v, want stanza size limit error", err)
+	}
+}
+
+func TestParseRejectsOversizedHeader(t *testing.T) {
+	var input bytes.Buffer
+	input.WriteString(intro)
+	for input.Len() <= MaxHeaderSize {
+		input.WriteString("-> test ")
+		input.WriteString(strings.Repeat("a", MaxStanzaSize-1024))
+		input.WriteString("\n\n")
+	}
+	input.WriteString("--- AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\n")
+
+	if _, _, err := Parse(&input); err == nil {
+		t.Fatal("Parse accepted an oversized header")
+	} else if !strings.Contains(err.Error(), "header exceeds") {
+		t.Fatalf("Parse error = %v, want header size limit error", err)
+	}
+}