fix: preserve subsecond healthCheckFailureDelay values

Formatting the delay with %.0f rounded subsecond durations such as
400ms down to 0s, silently discarding the configured delay. Use the
duration's own string form instead, which the shutdown manager parses
with time.ParseDuration.

Author: consideRatio

internal/infrastructure/kubernetes/proxy/resource.go

@@ -289,7 +289,7 @@ func expectedShutdownPreStopCommand(cfg *egv1a1.ShutdownConfig) []string {
 		if err != nil {
 			return nil
 		}
-		command = append(command, fmt.Sprintf("--health-check-failure-delay=%.0fs", d.Seconds()))
+		command = append(command, fmt.Sprintf("--health-check-failure-delay=%s", d.String()))
 	}
 
 	if cfg.DrainTimeout != nil {

internal/infrastructure/kubernetes/proxy/resource_test.go

@@ -211,6 +211,18 @@ func TestExpectedShutdownPreStopCommand(t *testing.T) {
 				"--min-drain-duration=5s",
 			},
 		},
+		{
+			name: "subsecond health check failure delay",
+			cfg: &egv1a1.ShutdownConfig{
+				HealthCheckFailureDelay: new(gwapiv1.Duration("400ms")),
+			},
+			expected: []string{
+				"envoy-gateway",
+				"envoy",
+				"shutdown",
+				"--health-check-failure-delay=400ms",
+			},
+		},
 	}
 
 	for _, tt := range tests {