refactor(handler,repo): replace strings.Contains error dispatch with typed sentinels (S-2)

Closes one 2026-04-24 audit finding (P2):

  - cat-s6-efc7f6f6bd50: 30 strings.Contains(err.Error(), ...) sites
    in internal/api/handler/ — brittle to repository-layer message
    changes, untyped against the actual failure mode.

Approach (Option B from prompt design notes):
  - New typed sentinels in internal/repository/errors.go:
      ErrNotFound, ErrForeignKeyConstraint
      IsForeignKeyError(err) helper (the only place substring
      matching at the lib/pq boundary is allowed; isolates the
      DB-driver string knowledge to one function).
  - New typed sentinel in internal/domain/errors.go:
      ErrValidation (reserved for future per-entity validation
      wrappers; not yet used by all handlers).
  - 49 sites in internal/repository/postgres/*.go updated to wrap
    sql.ErrNoRows-derived errors via fmt.Errorf("...: %w",
    repository.ErrNotFound).
  - 18 not-found handler sites + 2 FK-constraint handler sites
    refactored to errors.Is(err, repository.ErrNotFound) /
    repository.IsForeignKeyError(err).
  - 23 inline `fmt.Errorf("X not found")` test fixtures across
    handler tests rewrapped to wrap repository.ErrNotFound.
  - test_utils.go::ErrMockNotFound rewrapped to wrap
    repository.ErrNotFound; renewal_policy.go closure docblock
    updated to reflect the new convention.
  - integration test mockJobRepository.Get wraps repository.ErrNotFound.

CI regression guardrail:
- .github/workflows/ci.yml::"Forbidden strings.Contains(err.Error())
  regression guard (S-2)" greps for the three patterns ("not found",
  "violates foreign key", "RESTRICT") under internal/api/handler/
  and fails the build on regression.

Verification:
- go build ./... — clean
- go vet ./... — clean
- go test ./... -short -count=1 — all packages pass (handler +
  repository + service + integration)
- golangci-lint v2.11.4 run ./... — 0 issues
- S-2 guardrail dry-run on post-fix tree → empty (good)
- All sibling guardrails (S-1, G-3, D-1+D-2, B-1, L-1, H-1, C-1, F-1, P-1) pass

Audit findings closed:
- cat-s6-efc7f6f6bd50 (P2)

Deferred follow-ups:
- 6 domain-specific substring patterns still inline in handlers
  ("cannot approve", "cannot reject", "cannot be parsed",
  "no certificates found", "challenge password", "invalid"/
  "required" validation chains in profiles + agent_groups). Each
  needs its own typed sentinel, scoped per service. Documented
  by the S-2 CI guardrail's allowlist for closure-comments only.
- Per-entity not-found sentinels (Option A — ErrCertificateNotFound,
  ErrAgentNotFound, etc.) deferred. Generic ErrNotFound covers the
  current dispatch needs; per-entity precision would let handlers
  return entity-aware error bodies without a domain.Type field,
  but not blocking.

internal/api/handler/adversarial_query_test.go

@@ -522,7 +522,7 @@ func TestRevokeCertificate_AlreadyRevoked(t *testing.T) {
 func TestRevokeCertificate_NotFound(t *testing.T) {
 	handler, mock := newCertHandlerWithMock()
 	mock.RevokeCertificateFn = func(_ context.Context, id string, reason string, _ string) error {
-		return fmt.Errorf("certificate not found")
+		return fmt.Errorf("certificate not found: %w", ErrMockNotFound)
 	}
 
 	req := httptest.NewRequest(http.MethodPost, "/api/v1/certificates/mc-missing/revoke", strings.NewReader(`{"reason":"keyCompromise"}`))

internal/api/handler/agent_group_handler_test.go

@@ -33,7 +33,7 @@ func (m *MockAgentGroupService) GetAgentGroup(_ context.Context, id string) (*do
 	if m.GetAgentGroupFn != nil {
 		return m.GetAgentGroupFn(id)
 	}
-	return nil, fmt.Errorf("not found")
+	return nil, fmt.Errorf("not found: %w", ErrMockNotFound)
 }
 
 func (m *MockAgentGroupService) CreateAgentGroup(_ context.Context, group domain.AgentGroup) (*domain.AgentGroup, error) {

internal/api/handler/agent_groups.go

@@ -1,6 +1,8 @@
 package handler
 
 import (
+	"github.com/shankar0123/certctl/internal/repository"
+	"errors"
 	"context"
 	"encoding/json"
 	"net/http"
@@ -160,7 +162,7 @@ func (h AgentGroupHandler) UpdateAgentGroup(w http.ResponseWriter, r *http.Reque
 
 	updated, err := h.svc.UpdateAgentGroup(r.Context(), id, group)
 	if err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Agent group not found", requestID)
 			return
 		}
@@ -188,7 +190,7 @@ func (h AgentGroupHandler) DeleteAgentGroup(w http.ResponseWriter, r *http.Reque
 	}
 
 	if err := h.svc.DeleteAgentGroup(r.Context(), id); err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Agent group not found", requestID)
 			return
 		}

internal/api/handler/agent_retire_handler_test.go

@@ -3,7 +3,6 @@ package handler
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"net/http"
 	"net/http/httptest"
 	"testing"
@@ -142,7 +141,9 @@ func TestRetireAgentHandler_Sentinel_403(t *testing.T) {
 func TestRetireAgentHandler_NotFound_404(t *testing.T) {
 	mock, handler := agentRetireTestSetup()
 	mock.RetireAgentFn = func(agentID, actor string, force bool, reason string) (*service.AgentRetirementResult, error) {
-		return nil, errors.New("agent not found")
+		// S-2 closure (cat-s6-efc7f6f6bd50): wrap repository.ErrNotFound
+		// so the handler's errors.Is dispatch resolves to 404.
+		return nil, ErrMockNotFound
 	}
 
 	req := httptest.NewRequest(http.MethodDelete, "/api/v1/agents/unknown-id", nil)

internal/api/handler/agents.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"github.com/shankar0123/certctl/internal/repository"
 	"context"
 	"encoding/json"
 	"errors"
@@ -211,7 +212,7 @@ func (h AgentHandler) Heartbeat(w http.ResponseWriter, r *http.Request) {
 			ErrorWithRequestID(w, http.StatusGone, "Agent has been retired", requestID)
 			return
 		}
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Agent not found", requestID)
 			return
 		}
@@ -491,7 +492,7 @@ func (h AgentHandler) RetireAgent(w http.ResponseWriter, r *http.Request) {
 			JSON(w, http.StatusConflict, body)
 			return
 		}
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Agent not found", requestID)
 			return
 		}

internal/api/handler/certificate_handler_test.go

@@ -900,7 +900,7 @@ func TestRevokeCertificate_Handler_AlreadyRevoked(t *testing.T) {
 func TestRevokeCertificate_Handler_NotFound(t *testing.T) {
 	mock := &MockCertificateService{
 		RevokeCertificateFn: func(_ context.Context, certID string, reason string, _ string) error {
-			return fmt.Errorf("failed to fetch certificate: not found")
+			return fmt.Errorf("failed to fetch certificate: not found: %w", ErrMockNotFound)
 		},
 	}
 
@@ -1033,7 +1033,7 @@ func TestGetDERCRL_Success(t *testing.T) {
 			if issuerID == "iss-local" {
 				return derCRLData, nil
 			}
-			return nil, fmt.Errorf("issuer not found")
+			return nil, fmt.Errorf("issuer not found: %w", ErrMockNotFound)
 		},
 	}
 
@@ -1061,7 +1061,7 @@ func TestGetDERCRL_Success(t *testing.T) {
 func TestGetDERCRL_IssuerNotFound(t *testing.T) {
 	mock := &MockCertificateService{
 		GenerateDERCRLFn: func(_ context.Context, issuerID string) ([]byte, error) {
-			return nil, fmt.Errorf("issuer not found")
+			return nil, fmt.Errorf("issuer not found: %w", ErrMockNotFound)
 		},
 	}
 
@@ -1118,7 +1118,7 @@ func TestHandleOCSP_Success(t *testing.T) {
 			if issuerID == "iss-local" && serialHex == "12345" {
 				return ocspResponseBytes, nil
 			}
-			return nil, fmt.Errorf("certificate not found")
+			return nil, fmt.Errorf("certificate not found: %w", ErrMockNotFound)
 		},
 	}
 
@@ -1159,7 +1159,7 @@ func TestHandleOCSP_MissingSerial(t *testing.T) {
 func TestHandleOCSP_IssuerNotFound(t *testing.T) {
 	mock := &MockCertificateService{
 		GetOCSPResponseFn: func(_ context.Context, issuerID string, serialHex string) ([]byte, error) {
-			return nil, fmt.Errorf("issuer not found")
+			return nil, fmt.Errorf("issuer not found: %w", ErrMockNotFound)
 		},
 	}
 
@@ -1178,7 +1178,7 @@ func TestHandleOCSP_IssuerNotFound(t *testing.T) {
 func TestHandleOCSP_CertNotFound(t *testing.T) {
 	mock := &MockCertificateService{
 		GetOCSPResponseFn: func(_ context.Context, issuerID string, serialHex string) ([]byte, error) {
-			return nil, fmt.Errorf("certificate not found")
+			return nil, fmt.Errorf("certificate not found: %w", ErrMockNotFound)
 		},
 	}
 
@@ -1529,7 +1529,7 @@ func TestGetCertificateDeployments_Success(t *testing.T) {
 func TestGetCertificateDeployments_NotFound(t *testing.T) {
 	mock := &MockCertificateService{
 		GetCertificateDeploymentsFn: func(_ context.Context, certID string) ([]domain.DeploymentTarget, error) {
-			return nil, fmt.Errorf("certificate not found")
+			return nil, fmt.Errorf("certificate not found: %w", ErrMockNotFound)
 		},
 	}
 

internal/api/handler/certificates.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"errors"
 	"context"
 	"encoding/json"
 	"log/slog"
@@ -298,7 +299,7 @@ func (h CertificateHandler) UpdateCertificate(w http.ResponseWriter, r *http.Req
 
 	updated, err := h.svc.UpdateCertificate(r.Context(), id, cert)
 	if err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Certificate not found", requestID)
 			return
 		}
@@ -327,7 +328,7 @@ func (h CertificateHandler) ArchiveCertificate(w http.ResponseWriter, r *http.Re
 	}
 
 	if err := h.svc.ArchiveCertificate(r.Context(), id); err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Certificate not found", requestID)
 			return
 		}
@@ -373,7 +374,7 @@ func (h CertificateHandler) GetCertificateVersions(w http.ResponseWriter, r *htt
 
 	versions, total, err := h.svc.GetCertificateVersions(r.Context(), certID, page, perPage)
 	if err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Certificate not found", requestID)
 			return
 		}

internal/api/handler/discovery_handler_test.go

@@ -300,7 +300,7 @@ func TestGetDiscovered_Success(t *testing.T) {
 			if id == "dcert-1" {
 				return cert, nil
 			}
-			return nil, fmt.Errorf("not found")
+			return nil, fmt.Errorf("not found: %w", ErrMockNotFound)
 		},
 	}
 
@@ -331,7 +331,7 @@ func TestGetDiscovered_Success(t *testing.T) {
 func TestGetDiscovered_NotFound(t *testing.T) {
 	mock := &MockDiscoveryService{
 		GetDiscoveredFn: func(ctx context.Context, id string) (*domain.DiscoveredCertificate, error) {
-			return nil, fmt.Errorf("not found")
+			return nil, fmt.Errorf("not found: %w", ErrMockNotFound)
 		},
 	}
 
@@ -412,7 +412,7 @@ func TestClaimDiscovered_MissingManagedCertID(t *testing.T) {
 func TestClaimDiscovered_NotFound(t *testing.T) {
 	mock := &MockDiscoveryService{
 		ClaimDiscoveredFn: func(ctx context.Context, id string, managedCertID string, actor string) error {
-			return fmt.Errorf("discovered certificate not found")
+			return fmt.Errorf("discovered certificate not found: %w", ErrMockNotFound)
 		},
 	}
 
@@ -442,7 +442,7 @@ func TestDismissDiscovered_Success(t *testing.T) {
 			if id == "dcert-1" {
 				return nil
 			}
-			return fmt.Errorf("not found")
+			return fmt.Errorf("not found: %w", ErrMockNotFound)
 		},
 	}
 

internal/api/handler/export.go

@@ -1,6 +1,8 @@
 package handler
 
 import (
+	"github.com/shankar0123/certctl/internal/repository"
+	"errors"
 	"context"
 	"encoding/json"
 	"log/slog"
@@ -46,7 +48,7 @@ func (h ExportHandler) ExportPEM(w http.ResponseWriter, r *http.Request) {
 
 	result, err := h.svc.ExportPEM(r.Context(), id)
 	if err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Certificate not found", requestID)
 			return
 		}
@@ -94,7 +96,7 @@ func (h ExportHandler) ExportPKCS12(w http.ResponseWriter, r *http.Request) {
 
 	pfxData, err := h.svc.ExportPKCS12(r.Context(), id, req.Password)
 	if err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Certificate not found", requestID)
 			return
 		}

internal/api/handler/export_handler_test.go

@@ -110,7 +110,7 @@ func TestExportPEM_Download(t *testing.T) {
 func TestExportPEM_NotFound(t *testing.T) {
 	mockSvc := &MockExportService{
 		ExportPEMFn: func(_ context.Context, _ string) (*service.ExportPEMResult, error) {
-			return nil, fmt.Errorf("certificate not found")
+			return nil, fmt.Errorf("certificate not found: %w", ErrMockNotFound)
 		},
 	}
 	h := NewExportHandler(mockSvc)
@@ -216,7 +216,7 @@ func TestExportPKCS12_EmptyPassword(t *testing.T) {
 func TestExportPKCS12_NotFound(t *testing.T) {
 	mockSvc := &MockExportService{
 		ExportPKCS12Fn: func(_ context.Context, _ string, _ string) ([]byte, error) {
-			return nil, fmt.Errorf("certificate not found")
+			return nil, fmt.Errorf("certificate not found: %w", ErrMockNotFound)
 		},
 	}
 	h := NewExportHandler(mockSvc)

internal/api/handler/issuers.go

@@ -1,6 +1,8 @@
 package handler
 
 import (
+	"github.com/shankar0123/certctl/internal/repository"
+	"errors"
 	"context"
 	"encoding/json"
 	"log/slog"
@@ -210,9 +212,9 @@ func (h IssuerHandler) DeleteIssuer(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if err := h.svc.DeleteIssuer(r.Context(), id); err != nil {
-		if strings.Contains(err.Error(), "violates foreign key") || strings.Contains(err.Error(), "RESTRICT") {
+		if repository.IsForeignKeyError(err) {
 			ErrorWithRequestID(w, http.StatusConflict, "Cannot delete issuer: certificates are still using this issuer", requestID)
-		} else if strings.Contains(err.Error(), "not found") {
+		} else if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Issuer not found", requestID)
 		} else {
 			ErrorWithRequestID(w, http.StatusInternalServerError, "Failed to delete issuer", requestID)

internal/api/handler/job_handler_test.go

@@ -383,7 +383,7 @@ func TestApproveJob_Success(t *testing.T) {
 func TestApproveJob_NotFound(t *testing.T) {
 	mock := &MockJobService{
 		ApproveJobFn: func(id, actor string) error {
-			return fmt.Errorf("job not found: no rows")
+			return fmt.Errorf("job not found: no rows: %w", ErrMockNotFound)
 		},
 	}
 
@@ -527,7 +527,7 @@ func TestRejectJob_NoReason(t *testing.T) {
 func TestRejectJob_NotFound(t *testing.T) {
 	mock := &MockJobService{
 		RejectJobFn: func(id, reason, actor string) error {
-			return fmt.Errorf("job not found: no rows")
+			return fmt.Errorf("job not found: no rows: %w", ErrMockNotFound)
 		},
 	}
 

internal/api/handler/jobs.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"github.com/shankar0123/certctl/internal/repository"
 	"context"
 	"encoding/json"
 	"errors"
@@ -167,7 +168,7 @@ func (h JobHandler) ApproveJob(w http.ResponseWriter, r *http.Request) {
 				requestID)
 			return
 		}
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Job not found", requestID)
 			return
 		}
@@ -213,7 +214,7 @@ func (h JobHandler) RejectJob(w http.ResponseWriter, r *http.Request) {
 	actor := resolveActor(r.Context())
 
 	if err := h.svc.RejectJob(r.Context(), jobID, body.Reason, actor); err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Job not found", requestID)
 			return
 		}

internal/api/handler/network_scan_handler_test.go

@@ -27,7 +27,7 @@ func (m *mockNetworkScanService) GetTarget(ctx context.Context, id string) (*dom
 			return t, nil
 		}
 	}
-	return nil, fmt.Errorf("not found: %s", id)
+	return nil, fmt.Errorf("not found: %w", ErrMockNotFound)
 }
 
 func (m *mockNetworkScanService) CreateTarget(ctx context.Context, target *domain.NetworkScanTarget) (*domain.NetworkScanTarget, error) {
@@ -48,7 +48,7 @@ func (m *mockNetworkScanService) UpdateTarget(ctx context.Context, id string, ta
 			return t, nil
 		}
 	}
-	return nil, fmt.Errorf("not found: %s", id)
+	return nil, fmt.Errorf("not found: %w", ErrMockNotFound)
 }
 
 func (m *mockNetworkScanService) DeleteTarget(ctx context.Context, id string) error {
@@ -58,7 +58,7 @@ func (m *mockNetworkScanService) DeleteTarget(ctx context.Context, id string) er
 			return nil
 		}
 	}
-	return fmt.Errorf("not found: %s", id)
+	return fmt.Errorf("not found: %w", ErrMockNotFound)
 }
 
 func (m *mockNetworkScanService) TriggerScan(ctx context.Context, targetID string) (*domain.DiscoveryScan, error) {
@@ -71,7 +71,7 @@ func (m *mockNetworkScanService) TriggerScan(ctx context.Context, targetID strin
 			}, nil
 		}
 	}
-	return nil, fmt.Errorf("not found: %s", targetID)
+	return nil, fmt.Errorf("not found: %w", ErrMockNotFound)
 }
 
 func TestListNetworkScanTargets(t *testing.T) {

internal/api/handler/notifications.go

@@ -1,6 +1,8 @@
 package handler
 
 import (
+	"github.com/shankar0123/certctl/internal/repository"
+	"errors"
 	"context"
 	"net/http"
 	"strconv"
@@ -170,7 +172,7 @@ func (h NotificationHandler) RequeueNotification(w http.ResponseWriter, r *http.
 	notificationID := parts[0]
 
 	if err := h.svc.RequeueNotification(r.Context(), notificationID); err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Notification not found", requestID)
 			return
 		}

internal/api/handler/owners.go

@@ -1,6 +1,8 @@
 package handler
 
 import (
+	"github.com/shankar0123/certctl/internal/repository"
+	"errors"
 	"context"
 	"encoding/json"
 	"net/http"
@@ -184,9 +186,9 @@ func (h OwnerHandler) DeleteOwner(w http.ResponseWriter, r *http.Request) {
 	id = parts[0]
 
 	if err := h.svc.DeleteOwner(r.Context(), id); err != nil {
-		if strings.Contains(err.Error(), "violates foreign key") || strings.Contains(err.Error(), "RESTRICT") {
+		if repository.IsForeignKeyError(err) {
 			ErrorWithRequestID(w, http.StatusConflict, "Cannot delete owner: certificates are still assigned to this owner", requestID)
-		} else if strings.Contains(err.Error(), "not found") {
+		} else if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Owner not found", requestID)
 		} else {
 			ErrorWithRequestID(w, http.StatusInternalServerError, "Failed to delete owner", requestID)

internal/api/handler/profiles.go

@@ -1,6 +1,8 @@
 package handler
 
 import (
+	"github.com/shankar0123/certctl/internal/repository"
+	"errors"
 	"context"
 	"encoding/json"
 	"net/http"
@@ -162,7 +164,7 @@ func (h ProfileHandler) UpdateProfile(w http.ResponseWriter, r *http.Request) {
 
 	updated, err := h.svc.UpdateProfile(r.Context(), id, profile)
 	if err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Profile not found", requestID)
 			return
 		}
@@ -195,7 +197,7 @@ func (h ProfileHandler) DeleteProfile(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if err := h.svc.DeleteProfile(r.Context(), id); err != nil {
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Profile not found", requestID)
 			return
 		}

internal/api/handler/renewal_policy.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"github.com/shankar0123/certctl/internal/repository"
 	"context"
 	"encoding/json"
 	"errors"
@@ -26,14 +27,14 @@ type RenewalPolicyService interface {
 
 // RenewalPolicyHandler serves /api/v1/renewal-policies CRUD endpoints.
 //
-// G-1 design note: the service-level `ErrRenewalPolicyDuplicateName` /
+// G-1 + S-2 design note: the service-level `ErrRenewalPolicyDuplicateName` /
 // `ErrRenewalPolicyInUse` sentinels alias the repository sentinels (same var
-// identity), so `errors.Is` walks transparently across layers. Delete/Update
-// not-found detection intentionally uses a `strings.Contains(err.Error(),
-// "not found")` substring check — the repo wraps `sql.ErrNoRows` as
-// `fmt.Errorf("renewal policy not found: %s", id)` which strips the sentinel,
-// and the handler red-tests' `ErrMockNotFound = errors.New("mock not found
-// error")` follows the same substring convention.
+// identity), so `errors.Is` walks transparently across layers. S-2 closure
+// (cat-s6-efc7f6f6bd50) extends the same convention to not-found detection:
+// repos now wrap `sql.ErrNoRows` via `fmt.Errorf("X not found: %w",
+// repository.ErrNotFound)`, handler dispatch uses
+// `errors.Is(err, repository.ErrNotFound)`, and `ErrMockNotFound` in
+// test_utils.go wraps the same sentinel so the mocks still resolve to 404.
 type RenewalPolicyHandler struct {
 	svc RenewalPolicyService
 }
@@ -191,7 +192,7 @@ func (h RenewalPolicyHandler) UpdateRenewalPolicy(w http.ResponseWriter, r *http
 			ErrorWithRequestID(w, http.StatusConflict, "A renewal policy with that name already exists", requestID)
 			return
 		}
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Renewal policy not found", requestID)
 			return
 		}
@@ -231,7 +232,7 @@ func (h RenewalPolicyHandler) DeleteRenewalPolicy(w http.ResponseWriter, r *http
 			ErrorWithRequestID(w, http.StatusConflict, "Renewal policy is still referenced by managed certificates", requestID)
 			return
 		}
-		if strings.Contains(err.Error(), "not found") {
+		if errors.Is(err, repository.ErrNotFound) {
 			ErrorWithRequestID(w, http.StatusNotFound, "Renewal policy not found", requestID)
 			return
 		}

internal/api/handler/test_utils.go

@@ -1,11 +1,22 @@
 package handler
 
-import "errors"
+import (
+	"fmt"
 
-var (
-	// Mock errors for testing
-	ErrMockServiceFailed = errors.New("mock service error")
-	ErrMockNotFound      = errors.New("mock not found error")
-	ErrMockUnauthorized  = errors.New("mock unauthorized error")
-	ErrMockConflict      = errors.New("mock conflict error")
+	"github.com/shankar0123/certctl/internal/repository"
+)
+
+// Mock errors for testing.
+//
+// S-2 closure (cat-s6-efc7f6f6bd50): ErrMockNotFound now wraps
+// repository.ErrNotFound via fmt.Errorf("...: %w", ...) so the
+// post-S-2 handler dispatch — which uses errors.Is(err,
+// repository.ErrNotFound) instead of strings.Contains — still
+// resolves the mock to a 404. The error message text is preserved
+// for log inspection; only the wrapping changes.
+var (
+	ErrMockServiceFailed = fmt.Errorf("mock service error")
+	ErrMockNotFound      = fmt.Errorf("mock not found error: %w", repository.ErrNotFound)
+	ErrMockUnauthorized  = fmt.Errorf("mock unauthorized error")
+	ErrMockConflict      = fmt.Errorf("mock conflict error")
 )