repo,service: introduce WithinTx and atomic audit rows for issue/renew/revoke

Closes the #3 acquisition-readiness blocker from the 2026-05-01 issuer
coverage audit (Part 1.5 finding #1: audit row not transactional with
issuance). AuditRepository.Create previously ran on the package-level
*sql.DB while the certificate insert / version insert / revocation
insert ran on independent connections — a failed audit INSERT after
a successful operation INSERT was silently lost. SOX §404 over IT
general controls, PCI-DSS §10 audit logging, HIPAA §164.312(b) audit
controls, and CA/B Forum Baseline Requirements §5.4.1 audit log
records all presume audit-with-operation atomicity.

Design — Option A (Querier abstraction). The chosen pattern: a shared
repository.Querier interface (subset of *sql.DB and *sql.Tx) plus a
postgres.WithinTx helper that begins a tx, runs fn, commits on nil
error, rolls back on error or panic, and returns the wrapped result.
Repository methods that participate in a service-layer transaction
expose a *WithTx variant taking repository.Querier; the bare methods
remain for stand-alone use. A repository.Transactor abstracts the
"begin tx, run fn, commit/rollback" lifecycle so service-layer code
runs multi-write operations atomically without holding *sql.DB
directly. Option B (UnitOfWork) was considered but adds boilerplate
without behavioral benefit for the current scope. Option C
(context-carried tx) was explicitly rejected — it hides the
transactional boundary from the type system, reproducing the class
of bug we're fixing.

This commit:
- Adds internal/repository/querier.go with the Querier interface
  (compile-time guards that *sql.DB and *sql.Tx satisfy it) and the
  Transactor interface for service-layer use.
- Adds internal/repository/postgres/tx.go with the WithinTx helper
  (begin/fn/commit/rollback with panic recovery) and a transactor
  type that satisfies repository.Transactor.
- Adds CreateWithTx variants on AuditRepository, CertificateRepository
  (Create + Update + CreateVersion), and RevocationRepository.
  Existing bare methods now delegate to the *WithTx variant using
  the package-level *sql.DB so existing call sites are
  behavior-preserving.
- Updates repository/interfaces.go: AuditRepository, CertificateRepository,
  and RevocationRepository declare the new *WithTx methods. Adds an
  atomicity contract doc-comment on AuditRepository pointing at
  WithinTx + the audit blocker.
- Adds AuditService.RecordEventWithTx, mirroring RecordEvent but
  routing through CreateWithTx so the audit row is part of the
  caller's transaction. Same redaction + marshalling contract.
- Refactors three audit-emitting service paths to use Transactor.WithinTx
  when SetTransactor was wired, with a legacy fallback for backward
  compat:
    * CertificateService.Create — cert insert + audit row in one tx.
    * RevocationSvc.RevokeCertificateWithActor — cert status update +
      revocation row + audit row in one tx. The OCSP cache invalidate
      remains best-effort (out of scope per the prompt).
    * RenewalService CompleteServerRenewal — cert version insert +
      cert update + audit row in one tx. Job status update stays
      outside the audit-atomicity scope (job state lives outside
      the operator-facing audit trail).
- Adds SetTransactor on CertificateService, RevocationSvc, and
  RenewalService. cmd/server/main.go wires a single Transactor
  instance shared across all three so all audit-emitting paths run
  their writes in transactions backed by the same *sql.DB handle.
- Updates 5 mock implementations to satisfy the new interface methods:
  mockCertRepo (testutil_test.go), mockCertRepoWithGetError
  (shortlived_test.go), fakeRevocationRepo (crl_cache_test.go),
  intuneE2EAuditRepo (scep_intune_e2e_test.go), and the integration-
  test mocks (lifecycle_test.go: mockCertificateRepository,
  mockAuditRepository, mockRevocationRepository). All *WithTx mocks
  ignore the Querier and delegate to the bare method (mocks have no
  DB; in-memory state is shared regardless of "tx").
- Adds a service-layer test mockTransactor with BeginTxErr and
  CommitErr knobs so the atomic-audit tests can assert error
  propagation through the transactional boundary.
- Adds internal/repository/postgres/tx_test.go: unit-level test that
  WithinTx surfaces "begin tx" wrap when BeginTx fails, and that
  Transactor.WithinTx delegates correctly. Real-Postgres rollback
  semantics are covered by the testcontainers tests in the postgres
  package — sandbox disk pressure prevented adding a sqlmock dep
  for the in-fn / commit-failure unit test, so those scenarios are
  exercised through atomic_audit_test.go using the mockTransactor's
  CommitErr / BeginTxErr fields.
- Adds internal/service/atomic_audit_test.go:
    * TestCertificateService_Create_AtomicWithTx — asserts audit
      insert failure inside the tx surfaces as the operation's error
      (closes the blocker contract).
    * TestCertificateService_Create_LegacyPathLogs — pins the
      backward-compat behavior when SetTransactor isn't wired:
      audit failure is logged-not-failed, matching pre-fix.
    * TestCertificateService_Create_TransactorBeginFailure — BeginTx
      error path: operation fails, no cert insert, no audit insert.
    * TestCertificateService_Create_TransactorCommitFailure —
      Commit error after successful in-fn writes surfaces as the
      operation's error. Real Postgres can fail Commit on
      serialization conflicts; the service must report this.

Out of scope (separate follow-up commits, same shape):
- Issuer CRUD audit atomicity.
- Target CRUD audit atomicity.
- Agent retire (already transactional via RetireAgentWithCascade;
  verified, not changed).
- Renewal-policy CRUD audit atomicity.
- Owner/team/agent-group CRUD audit atomicity.
- Discovery / health-check audit atomicity.

Verified locally:
- gofmt -l . clean
- go vet ./... clean
- staticcheck ./... clean
- golangci-lint run --timeout 5m ./... → 0 issues
- go test -short -count=1 ./internal/service/ green
- go test -short -count=1 ./internal/api/handler/ green
- go test -short -count=1 ./internal/integration/ green
- go test -short -count=1 ./internal/repository/postgres/ green
- go build ./... success

Audit reference: cowork/issuer-coverage-audit-2026-05-01/RESULTS.md
Top-10 fix #3 (Part 3, narrative section).

internal/service/certificate.go

@@ -19,6 +19,13 @@ type CertificateService struct {
 	auditService  *AuditService
 	revSvc        *RevocationSvc
 	caSvc         *CAOperationsSvc
+	// tx, when set, wraps the issuance write (cert insert + audit row)
+	// in a single transaction so the audit row cannot be silently lost
+	// after a successful cert insert. Closes the #3 audit-readiness
+	// blocker (atomic audit rows). Optional via SetTransactor — when
+	// nil, Create falls back to the legacy non-transactional path
+	// (cert.Create + best-effort RecordEvent) for backward compatibility.
+	tx repository.Transactor
 	// crlCacheSvc, when set, makes GenerateDERCRL serve from the
 	// pre-generated cache instead of regenerating per request. Bundle
 	// CRL/OCSP-Responder Phase 4. Optional; when nil GenerateDERCRL
@@ -40,6 +47,16 @@ func NewCertificateService(
 	}
 }
 
+// SetTransactor wires a Transactor for atomic issuance (cert insert +
+// audit row) and atomic revocation (cert update + revocation row + audit
+// row). Closes the #3 acquisition-readiness blocker from the 2026-05-01
+// issuer coverage audit. Optional — when nil, Create falls back to the
+// legacy non-transactional path for backward compat with callers that
+// haven't been updated.
+func (s *CertificateService) SetTransactor(tx repository.Transactor) {
+	s.tx = tx
+}
+
 // SetRevocationSvc sets the revocation service.
 func (s *CertificateService) SetRevocationSvc(svc *RevocationSvc) {
 	s.revSvc = svc
@@ -133,19 +150,37 @@ func (s *CertificateService) Create(ctx context.Context, cert *domain.ManagedCer
 		}
 	}
 
-	// Store certificate
+	auditDetails := map[string]interface{}{"common_name": cert.CommonName}
+
+	// Atomic path (production): cert insert + audit row in a single
+	// transaction. Closes the #3 audit-readiness blocker — if the audit
+	// insert fails after the cert insert, the cert insert rolls back so
+	// the operator sees the failure and the audit trail is never silently
+	// incomplete.
+	if s.tx != nil {
+		return s.tx.WithinTx(ctx, func(q repository.Querier) error {
+			if err := s.certRepo.CreateWithTx(ctx, q, cert); err != nil {
+				return fmt.Errorf("failed to create certificate: %w", err)
+			}
+			if err := s.auditService.RecordEventWithTx(ctx, q, actor, domain.ActorTypeUser,
+				"certificate_created", "certificate", cert.ID, auditDetails); err != nil {
+				return fmt.Errorf("failed to record audit event: %w", err)
+			}
+			return nil
+		})
+	}
+
+	// Legacy non-transactional path — kept for callers that haven't
+	// wired SetTransactor yet. Fails open on audit-insert failure (logs
+	// and returns success), which is the pre-fix behavior; do not
+	// rely on this path for compliance-relevant audit trails.
 	if err := s.certRepo.Create(ctx, cert); err != nil {
 		return fmt.Errorf("failed to create certificate: %w", err)
 	}
-
-	// Record audit event
 	if err := s.auditService.RecordEvent(ctx, actor, domain.ActorTypeUser,
-		"certificate_created", "certificate", cert.ID,
-		map[string]interface{}{"common_name": cert.CommonName}); err != nil {
-		// Log but don't fail the operation
+		"certificate_created", "certificate", cert.ID, auditDetails); err != nil {
 		slog.Error("failed to record audit event", "error", err)
 	}
-
 	return nil
 }