fix(scep-intune): close 11 audit gaps from 2026-04-29 pre-tag review

Closes the eleven gaps identified in the pre-v2.1.0 audit of the SCEP
RFC 8894 + Intune master bundle (cowork/scep-bundle-gap-closure-prompt.md).
Constitutional rule from cowork/CLAUDE.md::Operating Rules — 'Always
take the complete path, not the easy path' — drove this closure: each
gap was a load-bearing wire that crossed multiple layers (config →
validator → service wire-up → tests → docs) and shipping the bundle
without them would have produced lying-field footguns where operator-
visible config options stored values without affecting behavior.

WHAT LANDS:

Phase A — Clock-skew tolerance (master prompt §15 hazard closure)
  internal/scep/intune/challenge.go: ValidateChallenge migrated from
  positional args to ValidateOptions{} struct; new ClockSkewTolerance
  field with default 0 (strict). 24 call sites updated mechanically.
  Asymmetric application: now+tolerance >= iat AND now-tolerance < exp.
  internal/config/config.go: SCEPIntuneProfileConfig.ClockSkewTolerance
  default 60s + Validate() refusal when >= ChallengeValidity.
  cmd/server/main.go: SetIntuneIntegration signature extended;
  per-profile env-var loader honors CERTCTL_SCEP_PROFILE_<NAME>_INTUNE_CLOCK_SKEW_TOLERANCE.
  internal/service/scep.go: intuneClockSkew field + IntuneStatsSnapshot
  surfaces clock_skew_tolerance_ns. web/src/api/types.ts mirrors.
  4 new tests in challenge_test.go covering accept-within-tolerance,
  reject-beyond-tolerance, accept-expired-within-tolerance,
  negative-treated-as-zero defensive normalization.
  docs/scep-intune.md updated with the new env var + time-bounds rule.

Phase B — unknown-version-rejected golden test
  internal/scep/intune/golden_helper_test.go: goldenUnknownVersionPayload
  helper + signGoldenChallengeAny generic signer.
  challenge_golden_test.go: TestGoldenChallenge_UnknownVersionRejected
  uses an in-process ECDSA fixture (the on-disk PEM was generated with
  a Go-stdlib version that produces different ecdsa.GenerateKey bytes
  from the current call). TestRegenerateGoldenFixtures emits the new
  unknown_version fixture file too.

Phase C — Two named Intune e2e tests
  internal/api/handler/scep_intune_e2e_test.go:
    TestSCEPIntuneEnrollment_RateLimited_E2E (cap=2 + 3 attempts; 3rd
    returns FAILURE+badRequest with rate_limited counter ticked)
    TestSCEPIntuneEnrollment_TrustAnchorSIGHUPReload_E2E (rotate
    on-disk PEM + holder.Reload(); old-key challenge fails with
    badMessageCheck; signature_invalid counter ticked)
  intuneE2EFixture struct extended with trustHolder + trustPath fields
  so tests can rotate.

Phase D — Four new ChromeOS hermetic tests (10 total now)
  internal/api/handler/scep_chromeos_test.go:
    _RAKeyMismatch — PKIMessage encrypted to wrong RA cert; handler
      rejects without reaching service.
    _3DESBackwardCompat — RFC 8894 §3.5.2 legacy fallback verified.
    _RSACSR + _ECDSACSR — explicit matrix-pair pinning.
  buildTestECDSACSR helper for ECDSA P-256 CSR construction;
  tripleDESCBCEncrypt mirrors aesCBCEncrypt for 3DES-CBC;
  assertChromeOSPositiveCertRep shared assertion.

Phase E — Per-profile counter isolation test
  internal/api/handler/scep_profile_counter_isolation_test.go:
    TestSCEPHandler_PerProfileIntuneCountersIsolated wires two
    SCEPService instances + drives distinct PKIMessages + asserts
    counter isolation. Guards against a future cmd/server/main.go
    refactor that shares a *intuneCounterTab across profiles.
  buildPerProfileIntuneFixture parameterized helper.

Phase F — Server-boot regression tests
  cmd/server/preflight_scep_intune_test.go: 3 named tests covering
  disabled-backward-compat, broken-config-with-PathID, expired-cert
  refusal. preflightSCEPIntuneTrustAnchor signature extended with
  pathID arg so error messages carry PathID= for operator log-grep.

Phase G — docs/connectors.md
  Four new subsections under §EST/SCEP Integration: multi-profile
  dispatch + mTLS sibling route + Intune Connector dispatcher + SCEP
  probe in network scanner. Each has a one-paragraph operator
  explanation + an env-var or endpoint table.

Phase H — Coverage uplift
  internal/service/scep_probe_persist_test.go: 5 unit tests on
  persistProbeResult (nil-safe + nil-repo-safe + repo-error swallow +
  nil-logger guard) + ListRecentSCEPProbes (empty-slice-not-nil + repo
  pass-through) + describeCertAlgorithm (RSA/ECDSA/QF1008-nil-curve
  defensive branch/Ed25519/DSA/empty). CI gates (service ≥70, handler
  ≥75) PASS at 70.9% / 79.3%.

Phase I — deploy/test integration variant
  deploy/test/scep_intune_e2e_test.go (//go:build integration):
    TestSCEPIntuneEnrollment_Integration + _RateLimited_Integration
    against the live docker-compose certctl container. Skip-when-
    stack-missing semantics so sandbox + CI both work.
  deploy/docker-compose.test.yml: new e2eintune SCEP profile env
  vars + bind-mount of deploy/test/fixtures/.
  deploy/test/fixtures/README.md: documents the deterministic trust
  anchor regeneration recipe.

VERIFICATION (sandbox):
  gofmt -d        — clean for all changed files
  staticcheck     — clean for intune + handler + config + service +
                    cmd/server packages
  go vet          — clean for the same packages
  go test -short  — green for intune (95.3% cov), service (70.9%),
                    handler (79.3%), config (94.0%), cmd/server (boot
                    path; my preflight tests cover the directly-
                    testable function), pkcs7 (80.5% informational)

DEFERRED (per closure prompt §7 out-of-scope):
  - V3-Pro Conditional Access gating + Microsoft Graph integration
  - Standalone certctl-scan CLI binary
  - OCSP rate-limiting, OCSP stapling, delta CRLs

Spec preserved at cowork/scep-bundle-gap-closure-prompt.md;
journal at cowork/scep-rfc8894-intune/progress.md (audit-closure
section appended).

internal/scep/intune/challenge_golden_test.go

@@ -6,6 +6,7 @@ import (
 	"flag"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -96,7 +97,22 @@ func TestRegenerateGoldenFixtures(t *testing.T) {
 		t.Fatalf("write tampered fixture: %v", err)
 	}
 
-	t.Logf("regenerated 4 fixture files in %s", testdataDir(t))
+	// Unknown-version fixture — same signing key + valid signature, but
+	// the payload carries a `version: "v999"` claim that the dispatcher
+	// does NOT have an unmarshaler for. ValidateChallenge MUST surface
+	// ErrChallengeUnknownVersion; the unknown-version fixture pins the
+	// dispatcher's defense against the inevitable Microsoft format
+	// change (master prompt §13 line 1848).
+	unknownVersionRaw := signGoldenChallengeAny(t, key, goldenUnknownVersionPayload())
+	if err := os.WriteFile(
+		filepath.Join(testdataDir(t), "intune_challenge_golden_unknown_version.txt"),
+		[]byte(unknownVersionRaw+"\n"),
+		0o600,
+	); err != nil {
+		t.Fatalf("write unknown-version fixture: %v", err)
+	}
+
+	t.Logf("regenerated 5 fixture files in %s", testdataDir(t))
 }
 
 // TestGoldenChallenge_Success — the documented happy-path: the success
@@ -107,7 +123,7 @@ func TestGoldenChallenge_Success(t *testing.T) {
 	trust := loadGoldenTrustAnchor(t)
 	raw := readGoldenFixture(t, "intune_challenge_golden_success.txt")
 
-	claim, err := ValidateChallenge(raw, trust, "https://certctl.example.com/scep/test", goldenChallengeNow)
+	claim, err := ValidateChallenge(raw, ValidateOptions{Trust: trust, ExpectedAudience: "https://certctl.example.com/scep/test", Now: goldenChallengeNow})
 	if err != nil {
 		t.Fatalf("ValidateChallenge success fixture: %v", err)
 	}
@@ -130,7 +146,7 @@ func TestGoldenChallenge_Expired(t *testing.T) {
 	trust := loadGoldenTrustAnchor(t)
 	raw := readGoldenFixture(t, "intune_challenge_golden_expired.txt")
 
-	_, err := ValidateChallenge(raw, trust, "", goldenChallengeNow)
+	_, err := ValidateChallenge(raw, ValidateOptions{Trust: trust, Now: goldenChallengeNow})
 	if !errors.Is(err, ErrChallengeExpired) {
 		t.Fatalf("got %v, want errors.Is(ErrChallengeExpired)", err)
 	}
@@ -143,7 +159,7 @@ func TestGoldenChallenge_TamperedSig(t *testing.T) {
 	trust := loadGoldenTrustAnchor(t)
 	raw := readGoldenFixture(t, "intune_challenge_golden_tampered_sig.txt")
 
-	_, err := ValidateChallenge(raw, trust, "https://certctl.example.com/scep/test", goldenChallengeNow)
+	_, err := ValidateChallenge(raw, ValidateOptions{Trust: trust, ExpectedAudience: "https://certctl.example.com/scep/test", Now: goldenChallengeNow})
 	if !errors.Is(err, ErrChallengeSignature) {
 		t.Fatalf("got %v, want errors.Is(ErrChallengeSignature)", err)
 	}
@@ -159,7 +175,7 @@ func TestGoldenChallenge_WrongAudienceReuse(t *testing.T) {
 	trust := loadGoldenTrustAnchor(t)
 	raw := readGoldenFixture(t, "intune_challenge_golden_success.txt")
 
-	_, err := ValidateChallenge(raw, trust, "https://attacker.example.com/scep/wrong", goldenChallengeNow)
+	_, err := ValidateChallenge(raw, ValidateOptions{Trust: trust, ExpectedAudience: "https://attacker.example.com/scep/wrong", Now: goldenChallengeNow})
 	if !errors.Is(err, ErrChallengeWrongAudience) {
 		t.Fatalf("got %v, want errors.Is(ErrChallengeWrongAudience)", err)
 	}
@@ -176,8 +192,56 @@ func TestGoldenChallenge_RotatedTrustAnchorRejects(t *testing.T) {
 	rotated := genTestECDSAConnector(t)
 	raw := readGoldenFixture(t, "intune_challenge_golden_success.txt")
 
-	_, err := ValidateChallenge(raw, []*x509.Certificate{rotated.cert}, "", goldenChallengeNow)
+	_, err := ValidateChallenge(raw, ValidateOptions{Trust: []*x509.Certificate{rotated.cert}, Now: goldenChallengeNow})
 	if !errors.Is(err, ErrChallengeSignature) {
 		t.Fatalf("got %v, want errors.Is(ErrChallengeSignature) when validated against a rotated trust anchor", err)
 	}
 }
+
+// TestGoldenChallenge_UnknownVersionRejected — master prompt §13 line
+// 1848 named acceptance criterion. A challenge whose payload carries a
+// `version: "v999"` claim (a value the dispatcher's
+// versionUnmarshalers map deliberately does NOT contain) MUST surface
+// ErrChallengeUnknownVersion regardless of whether the signature is
+// otherwise valid. This is the dispatcher's defense against the
+// inevitable Microsoft Connector format change — the day Microsoft
+// ships v2 and certctl's parser doesn't yet have a v2 unmarshaler, every
+// Intune enrollment lands here with a clear typed error rather than
+// crashing the SCEP handler with a confusing unmarshal panic.
+//
+// Why this test uses a fresh trust anchor instead of the on-disk
+// golden PEM: the on-disk PEM was generated with a Go-stdlib version
+// that produces different ECDSA key bytes from the current
+// generateGoldenTrustAnchor() call (the deterministic-PRNG +
+// ecdsa.GenerateKey pair has shifted across Go releases — the on-disk
+// public key bytes don't match what the current Go runtime regenerates
+// from the same seed). Rather than bake a stale trust anchor into the
+// regression, we generate a fresh ECDSA Connector keypair in-process
+// + use BOTH for signing AND for the validator's trust pool. The
+// regen target still emits a fixture file under testdata/ for the
+// operator-readable artifact; the test itself stays decoupled from
+// the on-disk PEM's drift.
+func TestGoldenChallenge_UnknownVersionRejected(t *testing.T) {
+	conn := genTestECDSAConnector(t)
+	raw := signTestChallengeES256_FixedWidth(t, conn, struct {
+		Version string `json:"version"`
+		challengePayloadV1
+	}{
+		Version:            "v999",
+		challengePayloadV1: goldenChallengePayload(),
+	})
+
+	_, err := ValidateChallenge(raw, ValidateOptions{
+		Trust: []*x509.Certificate{conn.cert},
+		Now:   goldenChallengeNow,
+	})
+	if !errors.Is(err, ErrChallengeUnknownVersion) {
+		t.Fatalf("got %v, want errors.Is(ErrChallengeUnknownVersion) for version=v999 claim", err)
+	}
+	// The error message MUST surface the specific version string so the
+	// operator's audit log narrows the diagnosis to "Microsoft shipped
+	// vN" rather than "something is wrong with the challenge."
+	if !strings.Contains(err.Error(), "v999") {
+		t.Errorf("error should contain the unknown version literal for operator audit log: %v", err)
+	}
+}