test: comprehensive test gap closure across 24 packages

Close coverage gaps identified by dual-audit (qualitative + quantitative).
New test files for config (0%→98%), router (0%→100%), handler validation,
health, audit, response helpers, webhook notifier (0%→88%), email notifier,
middleware (recovery, rate limiter), domain profile, service nil-safety,
config helpers, issuer bootstrap, and server bootstrap wiring. Expanded
existing tests for ACME (34%→42%), step-ca (42%→52%), F5, SSH, agent
(43%→63%), scheduler (88%→99%), renewal service, and issuerfactory.

All tests pass: go test -short, go vet, go test -race clean.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/api/middleware/recovery_test.go

@@ -0,0 +1,104 @@
+package middleware
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+// TestRecovery_CatchesPanic verifies that panic recovery middleware catches panics
+// and returns a 500 error response.
+func TestRecovery_CatchesPanic(t *testing.T) {
+	handler := Recovery(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		panic("test panic")
+	}))
+
+	req := httptest.NewRequest("GET", "/test", nil)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status %d, got %d", http.StatusInternalServerError, w.Code)
+	}
+
+	// Verify error response is present
+	if w.Body.Len() == 0 {
+		t.Error("expected error response body, got empty")
+	}
+}
+
+// TestRecovery_CatchesNilPanic verifies that recovery middleware handles nil panics.
+func TestRecovery_CatchesNilPanic(t *testing.T) {
+	handler := Recovery(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// This is unusual but valid in Go
+		panic(nil)
+	}))
+
+	req := httptest.NewRequest("GET", "/test", nil)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status %d, got %d", http.StatusInternalServerError, w.Code)
+	}
+}
+
+// TestRecovery_NoPanicPasses verifies that non-panicking handlers pass through normally.
+func TestRecovery_NoPanicPasses(t *testing.T) {
+	handler := Recovery(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("X-Test", "success")
+		w.WriteHeader(http.StatusOK)
+	}))
+
+	req := httptest.NewRequest("GET", "/test", nil)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("expected status %d, got %d", http.StatusOK, w.Code)
+	}
+
+	if w.Header().Get("X-Test") != "success" {
+		t.Error("expected custom header to be set")
+	}
+}
+
+// TestRecovery_StringPanic verifies recovery from string panics.
+func TestRecovery_StringPanic(t *testing.T) {
+	handler := Recovery(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		panic("string panic message")
+	}))
+
+	req := httptest.NewRequest("GET", "/test", nil)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status %d, got %d", http.StatusInternalServerError, w.Code)
+	}
+}
+
+// TestRecovery_ErrorPanic verifies recovery from error type panics.
+func TestRecovery_ErrorPanic(t *testing.T) {
+	testErr := &customError{msg: "test error"}
+	handler := Recovery(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		panic(testErr)
+	}))
+
+	req := httptest.NewRequest("GET", "/test", nil)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("expected status %d, got %d", http.StatusInternalServerError, w.Code)
+	}
+}
+
+// customError is a simple error type for testing.
+type customError struct {
+	msg string
+}
+
+func (e *customError) Error() string {
+	return e.msg
+}