tpm-enrol: pivot host enrolment to a Go binary, built out-of-VM

Replaces the shell/openssl-provider host enrolment (a35f2d6) with a static
Go + go-tpm binary, and moves BOTH host Go binaries out of the Packer VM.

fleet-enrol (files/enrol/, Go + go-tpm, no CGO):
  - talks to /dev/tpmrm0 DIRECTLY via transport.FromReadWriter(os.File) — no
    linuxtpm, so go-tpm is the only dep and there is NO tpm2-tools key-gen /
    openssl tpm2 provider / curl in the image (removes the biggest bench risk,
    the provider handle: key-ref).
  - ensures the ECDSA key @0x81010001, builds the CSR (crypto.Signer over the
    TPM key), POSTs CSR+context to the broker, shows the Plymouth fingerprint,
    polls /status, writes the leaf cert to NV 0x01800001.
  - tpmkey/ is an exported package so the TPM ceremony is tested against the
    go-tpm software simulator from a SEPARATE simtest/ module (CGO stays out of
    the shipped build). Transaction logic (mock broker) tested in-package.
  - deps pinned by go.sum (not vendored): the binary now builds on the CI
    runner, which has network — reproducible via pinned Go 1.26.4 + go.sum.

Out-of-VM build (decision): both fleet-enrol AND fleet-hostapi compile in the
CI "Build host Go binaries" step (Go 1.26.4, CGO off, -trimpath) and Packer
FILE-PROVISIONS the static binaries in. Dropped the in-VM `dnf install golang`
+ the 2d removal — the Rocky build image carries no Go toolchain / go-tpm tree.

Wiring:
  - tpm-enrol.sh: now a thin GATE (empty-NV check, pre-auth DHCP on en*,
    exec /usr/sbin/fleet-enrol, reboot-to-converge). module-setup.sh bundles the
    binary (asserted) + reverts the tpm2-openssl/curl installs.
  - diskless.pkr.hcl: file provisioners for both binaries; enrol installed to
    /usr/sbin before the initramfs build + fapolicyd-trusted; lsinitrd asserts
    fleet-enrol; dnf reverted to baseline (no tpm2-openssl/curl).
  - gitea-main-ci.yaml: Set up Go + build both binaries + run the simulator
    ceremony test, before packer validate.

TESTED here: transaction unit tests + the full TPM ceremony (key-gen -> persist
-> ECDSA sign -> CSR verify -> chunked NV write -> re-enrol) against the go-tpm
simulator. BENCH-VERIFY (real/swtpm, empty owner auth, pre-auth DHCP, Plymouth,
reboot-converge, prod HTTPS) tracked in docs/TODO.md #11.

files/enrol/simtest/tpmsim_test.go

@@ -0,0 +1,101 @@
+// Package simtest validates tpmkey's TPM ceremony against the go-tpm software
+// simulator (the MS TPM 2.0 reference). It lives in its own module so the CGO
+// simulator never enters the shipped fleet-enrol build; see go.mod.
+package simtest
+
+import (
+	"crypto/ecdsa"
+	"crypto/rand"
+	"crypto/sha256"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"testing"
+
+	"fleet-enrol/tpmkey"
+
+	"github.com/google/go-tpm-tools/simulator"
+	"github.com/google/go-tpm/tpm2"
+	"github.com/google/go-tpm/tpm2/transport"
+)
+
+func openSim(t *testing.T) transport.TPM {
+	t.Helper()
+	sim, err := simulator.Get()
+	if err != nil {
+		t.Fatalf("simulator: %v", err)
+	}
+	t.Cleanup(func() { sim.Close() })
+	return transport.FromReadWriter(sim)
+}
+
+func TestEnsureKeyAndSignCSR(t *testing.T) {
+	tpm := openSim(t)
+	const h = tpm2.TPMHandle(0x81010001)
+
+	signer, created, err := tpmkey.EnsureKey(tpm, h)
+	if err != nil {
+		t.Fatalf("EnsureKey: %v", err)
+	}
+	if !created {
+		t.Errorf("first EnsureKey should report created=true")
+	}
+	if _, ok := signer.Public().(*ecdsa.PublicKey); !ok {
+		t.Fatalf("signer public key is not ECDSA")
+	}
+
+	// idempotent: second call reuses the persistent key (same pubkey).
+	signer2, created2, err := tpmkey.EnsureKey(tpm, h)
+	if err != nil || created2 {
+		t.Fatalf("second EnsureKey: created=%v err=%v", created2, err)
+	}
+	if !signer.Public().(*ecdsa.PublicKey).Equal(signer2.Public()) {
+		t.Errorf("persistent key changed between calls")
+	}
+
+	// the TPM signer must produce a CSR that verifies — this is the exact
+	// openssl-tpm2-provider path the Go binary replaces.
+	tmpl := &x509.CertificateRequest{Subject: pkix.Name{CommonName: "fleet-host"}}
+	der, err := x509.CreateCertificateRequest(rand.Reader, tmpl, signer)
+	if err != nil {
+		t.Fatalf("CreateCertificateRequest with TPM signer: %v", err)
+	}
+	csr, err := x509.ParseCertificateRequest(der)
+	if err != nil {
+		t.Fatalf("parse CSR: %v", err)
+	}
+	if err := csr.CheckSignature(); err != nil {
+		t.Fatalf("CSR signature (TPM-signed) invalid: %v", err)
+	}
+
+	// raw signer sanity: sign a digest, verify with the public key.
+	dig := sha256.Sum256([]byte("hello"))
+	sig, err := signer.Sign(rand.Reader, dig[:], nil)
+	if err != nil {
+		t.Fatalf("sign: %v", err)
+	}
+	if !ecdsa.VerifyASN1(signer.Public().(*ecdsa.PublicKey), dig[:], sig) {
+		t.Fatalf("TPM ECDSA signature did not verify")
+	}
+}
+
+func TestNVWriteAndPresence(t *testing.T) {
+	tpm := openSim(t)
+	const nv = tpm2.TPMHandle(0x01800001)
+
+	if tpmkey.NVPresent(tpm, nv) {
+		t.Fatalf("NV should be empty on a fresh TPM")
+	}
+	// realistic cert-sized payload that also crosses the 512B write chunk.
+	want := make([]byte, 700)
+	rand.Read(want)
+	if err := tpmkey.WriteNVCert(tpm, nv, want); err != nil {
+		t.Fatalf("WriteNVCert: %v", err)
+	}
+	if !tpmkey.NVPresent(tpm, nv) {
+		t.Fatalf("NV should be present after write")
+	}
+	// re-write (re-enrolment) must succeed (undefine + redefine).
+	if err := tpmkey.WriteNVCert(tpm, nv, want[:400]); err != nil {
+		t.Fatalf("WriteNVCert rewrite: %v", err)
+	}
+}