cmd/hi: enable concurrent test execution

Remove the concurrent test prevention logic and update cleanup to use
run ID-based isolation, allowing multiple tests to run simultaneously.

Changes:
- cleanup: Add killTestContainersByRunID() to clean only containers
  belonging to a specific run, add cleanupStaleTestContainers() to
  remove only stopped/exited containers without affecting running tests
- docker: Remove RunningTestInfo, checkForRunningTests(), and related
  error types, update cleanupAfterTest() to use run ID-based cleanup
- run: Remove Force flag and concurrent test prevention check

The test runner now:
- Allows multiple concurrent test runs on the same Docker daemon
- Cleans only stale containers before tests (not running ones)
- Cleans only containers with matching run ID after tests
- Prints run ID and monitoring info for operator visibility

cmd/hi/run.go

@@ -6,7 +6,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"strings"
 	"time"
 
 	"github.com/creachadair/command"
@@ -14,65 +13,13 @@ import (
 
 var ErrTestPatternRequired = errors.New("test pattern is required as first argument or use --test flag")
 
-// formatRunningTestError creates a detailed error message about a running test.
-func formatRunningTestError(info *RunningTestInfo) error {
-	var msg strings.Builder
-	msg.WriteString("\n")
-	msg.WriteString("╔══════════════════════════════════════════════════════════════════╗\n")
-	msg.WriteString("║  Another integration test run is already in progress!            ║\n")
-	msg.WriteString("╚══════════════════════════════════════════════════════════════════╝\n")
-	msg.WriteString("\n")
-	msg.WriteString("Running test details:\n")
-	msg.WriteString(fmt.Sprintf("  Run ID:      %s\n", info.RunID))
-	msg.WriteString(fmt.Sprintf("  Container:   %s\n", info.ContainerName))
-
-	if info.TestPattern != "" {
-		msg.WriteString(fmt.Sprintf("  Test:        %s\n", info.TestPattern))
-	}
-
-	if !info.StartTime.IsZero() {
-		msg.WriteString(fmt.Sprintf("  Started:     %s\n", info.StartTime.Format("2006-01-02 15:04:05")))
-		msg.WriteString(fmt.Sprintf("  Running for: %s\n", formatDuration(info.Duration)))
-	}
-
-	msg.WriteString("\n")
-	msg.WriteString("Please wait for the current test to complete, or stop it with:\n")
-	msg.WriteString("  go run ./cmd/hi clean containers\n")
-	msg.WriteString("\n")
-	msg.WriteString("To monitor the running test:\n")
-	msg.WriteString(fmt.Sprintf("  docker logs -f %s\n", info.ContainerName))
-
-	return fmt.Errorf("%w\n%s", ErrAnotherRunInProgress, msg.String())
-}
-
-const secondsPerMinute = 60
-
-// formatDuration formats a duration in a human-readable way.
-func formatDuration(d time.Duration) string {
-	if d < time.Minute {
-		return fmt.Sprintf("%d seconds", int(d.Seconds()))
-	}
-
-	if d < time.Hour {
-		minutes := int(d.Minutes())
-		seconds := int(d.Seconds()) % secondsPerMinute
-
-		return fmt.Sprintf("%d minutes, %d seconds", minutes, seconds)
-	}
-
-	hours := int(d.Hours())
-	minutes := int(d.Minutes()) % secondsPerMinute
-
-	return fmt.Sprintf("%d hours, %d minutes", hours, minutes)
-}
-
 type RunConfig struct {
 	TestPattern   string        `flag:"test,Test pattern to run"`
 	Timeout       time.Duration `flag:"timeout,default=120m,Test timeout"`
 	FailFast      bool          `flag:"failfast,default=true,Stop on first test failure"`
 	UsePostgres   bool          `flag:"postgres,default=false,Use PostgreSQL instead of SQLite"`
 	GoVersion     string        `flag:"go-version,Go version to use (auto-detected from go.mod)"`
-	CleanBefore   bool          `flag:"clean-before,default=true,Clean resources before test"`
+	CleanBefore   bool          `flag:"clean-before,default=true,Clean stale resources before test"`
 	CleanAfter    bool          `flag:"clean-after,default=true,Clean resources after test"`
 	KeepOnFailure bool          `flag:"keep-on-failure,default=false,Keep containers on test failure"`
 	LogsDir       string        `flag:"logs-dir,default=control_logs,Control logs directory"`
@@ -80,7 +27,6 @@ type RunConfig struct {
 	Stats         bool          `flag:"stats,default=false,Collect and display container resource usage statistics"`
 	HSMemoryLimit float64       `flag:"hs-memory-limit,default=0,Fail test if any Headscale container exceeds this memory limit in MB (0 = disabled)"`
 	TSMemoryLimit float64       `flag:"ts-memory-limit,default=0,Fail test if any Tailscale container exceeds this memory limit in MB (0 = disabled)"`
-	Force         bool          `flag:"force,default=false,Kill any running test and start a new one"`
 }
 
 // runIntegrationTest executes the integration test workflow.
@@ -98,23 +44,6 @@ func runIntegrationTest(env *command.Env) error {
 		runConfig.GoVersion = detectGoVersion()
 	}
 
-	// Check if another test run is already in progress
-	runningTest, err := checkForRunningTests(env.Context())
-	if err != nil && !errors.Is(err, ErrNoRunningTests) {
-		log.Printf("Warning: failed to check for running tests: %v", err)
-	} else if runningTest != nil {
-		if runConfig.Force {
-			log.Printf("Force flag set, killing existing test run: %s", runningTest.RunID)
-
-			err = killTestContainers(env.Context())
-			if err != nil {
-				return fmt.Errorf("failed to kill existing test containers: %w", err)
-			}
-		} else {
-			return formatRunningTestError(runningTest)
-		}
-	}
-
 	// Run pre-flight checks
 	if runConfig.Verbose {
 		log.Printf("Running pre-flight system checks...")