Docs for the Rust version; benchmarks; build.sh fixes

README, CLAUDE.md, man pages, the user guide and its screenshot script
now describe the Rust build and the intentional behaviour changes, which
docs/MIGRATION.md lists. Go and Rust micro-benchmarks for the same
operations, and scripts/bench.sh for end-to-end comparison. build.sh
exports its tree root to the per-target jobs and keeps logs out of the
output directory; riscv64 musl builds use getrandom's raw syscall
backend, since zig's musl getrandom never reaches the kernel there.

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

oracle/go/internal/pqcrypt/oracle_bench_test.go

@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Test-only benchmarks for comparing with the Rust port (scripts/bench.sh).
+
+package pqcrypt
+
+import (
+	"bytes"
+	"io"
+	"testing"
+)
+
+func BenchmarkOracleDerive(b *testing.B) {
+	seed := pattern(32, 1)
+	for b.Loop() {
+		id, _ := NewPQIdentityFromSeed(0x0001, seed)
+		id.Close()
+	}
+}
+
+func BenchmarkOracleWrap(b *testing.B) {
+	id, _ := NewPQIdentityFromSeed(0x0001, pattern(32, 1))
+	r := id.Recipient()
+	fk := pattern(32, 2)
+	for b.Loop() {
+		r.Wrap(fk)
+	}
+}
+
+func BenchmarkOracleUnwrap(b *testing.B) {
+	id, _ := NewPQIdentityFromSeed(0x0001, pattern(32, 1))
+	st, _ := id.Recipient().Wrap(pattern(32, 2))
+	for b.Loop() {
+		if _, err := id.Unwrap(st); err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+// Whole-file encryption and decryption of 4 MiB: one vault object.
+func BenchmarkOracleObject4MiB(b *testing.B) {
+	id, _ := NewPQIdentityFromSeed(0x0001, pattern(32, 1))
+	pt := pattern(4<<20, 3)
+	var ct bytes.Buffer
+	b.SetBytes(int64(len(pt)))
+	for b.Loop() {
+		ct.Reset()
+		w, _ := Encrypt(&ct, id.Recipient())
+		w.Write(pt)
+		w.Close()
+		r, err := Decrypt(bytes.NewReader(ct.Bytes()), id)
+		if err != nil {
+			b.Fatal(err)
+		}
+		io.Copy(io.Discard, r)
+	}
+}

oracle/go/internal/stream/oracle_bench_test.go

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Test-only benchmarks for comparing with the Rust port (scripts/bench.sh).
+
+package stream
+
+import (
+	"bytes"
+	"io"
+	"testing"
+)
+
+// STREAM seal and open of 64 MiB, one goroutine (the sequential path).
+func BenchmarkOracleStream64MiB(b *testing.B) {
+	key := make([]byte, 32)
+	pt := make([]byte, 64<<20)
+	var ct bytes.Buffer
+	b.SetBytes(int64(len(pt)))
+	for b.Loop() {
+		ct.Reset()
+		w, _ := NewEncryptWriter(key, &ct)
+		w.Write(pt)
+		w.Close()
+		r, _ := NewDecryptReader(key, bytes.NewReader(ct.Bytes()))
+		io.Copy(io.Discard, r)
+	}
+}