Close M-004 (OCSP issuer binding) and M-005 (discovery actor propagation) coverage-gap findings

M-004 — OCSP issuer binding (composite key):
  The OCSP lookup path now binds (issuer_id, serial) as a composite key
  rather than resolving by serial alone. CertificateRepository and
  RevocationRepository gain GetByIssuerAndSerial methods; ca_operations.go
  scopes both lookups by the issuer_id path param. When no managed cert
  binds to that (issuer, serial) tuple, GetOCSPResponse constructs an
  RFC 6960 §2.2 'unknown' response (CertStatus=2) instead of the prior
  default 'good'. Short-lived cert exemption (profile TTL < 1h) is
  preserved. Real repo errors (non-sql.ErrNoRows) fail closed with a log.

  Regression coverage: internal/service/ca_operations_test.go
    - TestCAOperationsSvc_GetOCSPResponse_Unknown_CrossIssuer
    - TestCAOperationsSvc_GetOCSPResponse_Unknown_UnknownSerial

M-005 — Discovery Claim/Dismiss actor propagation:
  DiscoveryService.ClaimDiscovered and DismissDiscovered now accept an
  explicit 'actor string' parameter (propagation pattern mirrors
  bulk_revocation.go / revocation_svc.go). The handler layer passes
  resolveActor(r.Context()) — the named-key identity established by the
  M-002 auth unification — and the service falls back to 'api' (the same
  safe sentinel resolveActor uses when no auth context is present) only
  when the caller passes an empty string. Never falls back to 'operator'.

  Regression coverage: internal/service/discovery_test.go
    - TestDiscoveryService_ClaimDiscovered_AuditActor
    - TestDiscoveryService_DismissDiscovered_AuditActor
    - TestDiscoveryService_ClaimDiscovered_EmptyActorFallsBackToAPI
    - TestDiscoveryService_DismissDiscovered_EmptyActorFallsBackToAPI

Each new test asserts event.Actor matches the caller-supplied string (or
'api' on empty input) and explicitly asserts event.Actor != 'operator'
to lock in the historical fix intent.

Files:
  internal/api/handler/discovery.go          — pass resolveActor(ctx)
  internal/api/handler/discovery_handler_test.go — updated call sites
  internal/integration/lifecycle_test.go     — updated mock wiring
  internal/repository/interfaces.go          — GetByIssuerAndSerial on
                                               CertificateRepository +
                                               RevocationRepository
  internal/repository/postgres/certificate.go — composite key lookup
  internal/service/ca_operations.go          — (issuer_id, serial) scoping
  internal/service/ca_operations_test.go     — 2 new M-004 tests
  internal/service/discovery.go              — actor parameter + 'api' fallback
  internal/service/discovery_test.go         — 4 new M-005 tests
  internal/service/shortlived_test.go        — mock signature update
  internal/service/testutil_test.go          — mock GetByIssuerAndSerial

internal/service/ca_operations.go

@@ -2,6 +2,8 @@ package service
 
 import (
 	"context"
+	"database/sql"
+	"errors"
 	"fmt"
 	"log/slog"
 	"math/big"
@@ -139,23 +141,49 @@ func (s *CAOperationsSvc) GetOCSPResponse(ctx context.Context, issuerID string,
 
 	// Check if this (issuer_id, serial) is revoked — RFC 5280 §5.2.3 scoping.
 	rev, err := s.revocationRepo.GetByIssuerAndSerial(ctx, issuerID, serialHex)
-	if err != nil {
-		// Not revoked — return "good" status
+	if err == nil && rev != nil {
+		// Revoked
 		return issuerConn.SignOCSPResponse(ctx, OCSPSignRequest{
-			CertSerial: serial,
-			CertStatus: 0, // good
-			ThisUpdate: now,
-			NextUpdate: now.Add(1 * time.Hour),
+			CertSerial:       serial,
+			CertStatus:       1, // revoked
+			RevokedAt:        rev.RevokedAt,
+			RevocationReason: domain.CRLReasonCode(domain.RevocationReason(rev.Reason)),
+			ThisUpdate:       now,
+			NextUpdate:       now.Add(1 * time.Hour),
 		})
 	}
 
-	// Revoked
+	// Not revoked. Per RFC 6960 §2.2, we must only return "good" for a
+	// certificate that was actually issued by this CA. Verify the
+	// (issuer_id, serial) tuple maps to a real certificate in inventory
+	// before asserting "good"; otherwise return "unknown". This closes the
+	// coverage gap where forged/guessed serials would be accepted as valid
+	// because they had no revocation row (M-004).
+	if s.certRepo != nil {
+		cert, certErr := s.certRepo.GetByIssuerAndSerial(ctx, issuerID, serialHex)
+		if certErr != nil || cert == nil {
+			if certErr != nil && !errors.Is(certErr, sql.ErrNoRows) {
+				// Real repository failure — log but still fail closed with "unknown"
+				// rather than leaking a bogus "good" assertion.
+				slog.Warn("OCSP cert lookup failed; returning unknown",
+					"issuer_id", issuerID,
+					"serial", serialHex,
+					"error", certErr)
+			}
+			return issuerConn.SignOCSPResponse(ctx, OCSPSignRequest{
+				CertSerial: serial,
+				CertStatus: 2, // unknown
+				ThisUpdate: now,
+				NextUpdate: now.Add(1 * time.Hour),
+			})
+		}
+	}
+
+	// Known cert, not revoked — return "good"
 	return issuerConn.SignOCSPResponse(ctx, OCSPSignRequest{
-		CertSerial:       serial,
-		CertStatus:       1, // revoked
-		RevokedAt:        rev.RevokedAt,
-		RevocationReason: domain.CRLReasonCode(domain.RevocationReason(rev.Reason)),
-		ThisUpdate:       now,
-		NextUpdate:       now.Add(1 * time.Hour),
+		CertSerial: serial,
+		CertStatus: 0, // good
+		ThisUpdate: now,
+		NextUpdate: now.Add(1 * time.Hour),
 	})
 }