Fix config validation edge cases

internal/core/diagnostics/run_dir.go

@@ -12,7 +12,14 @@ import (
 	"gitea.maximumdirect.net/eric/notarius/internal/framework/contracts"
 )
 
-const defaultWorkDir = "/tmp/notarius"
+const (
+	defaultWorkDir                = "/tmp/notarius"
+	maxRunDirectoryCreateAttempts = 16
+)
+
+var utcNow = func() time.Time {
+	return time.Now().UTC()
+}
 
 // RunDirectory represents a per-run diagnostics directory.
 type RunDirectory struct {
@@ -77,18 +84,27 @@ func NewRunDirectory(workDir string, retention RetentionMode) (*RunDirectory, er
 		return nil, fmt.Errorf("create diagnostics work directory %q: %w", workDir, err)
 	}
 
-	createdAt := time.Now().UTC()
-	runID := fmt.Sprintf("run-%d", createdAt.UnixNano())
-	runPath := filepath.Join(workDir, runID)
-	if err := os.Mkdir(runPath, 0o755); err != nil {
-		return nil, fmt.Errorf("create diagnostics run directory %q: %w", runPath, err)
+	var lastRunPath string
+	for attempt := 0; attempt < maxRunDirectoryCreateAttempts; attempt++ {
+		createdAt := utcNow()
+		runID := fmt.Sprintf("run-%d", createdAt.UnixNano())
+		runPath := filepath.Join(workDir, runID)
+		lastRunPath = runPath
+		if err := os.Mkdir(runPath, 0o755); err != nil {
+			if os.IsExist(err) {
+				continue
+			}
+			return nil, fmt.Errorf("create diagnostics run directory %q: %w", runPath, err)
+		}
+
+		return &RunDirectory{
+			path:      runPath,
+			retention: retention,
+			createdAt: createdAt,
+		}, nil
 	}
 
-	return &RunDirectory{
-		path:      runPath,
-		retention: retention,
-		createdAt: createdAt,
-	}, nil
+	return nil, fmt.Errorf("create diagnostics run directory %q: exhausted unique run ID attempts", lastRunPath)
 }
 
 func (r *RunDirectory) Path() string {

internal/core/diagnostics/run_dir_test.go

@@ -2,6 +2,7 @@ package diagnostics
 
 import (
 	"encoding/json"
+	"fmt"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -35,6 +36,57 @@ func TestNewRunDirectoryCreatesRunDirectoryAndRunID(t *testing.T) {
 	}
 }
 
+func TestNewRunDirectoryRetriesOnRunIDCollision(t *testing.T) {
+	workDir := t.TempDir()
+	first := time.Unix(0, 100).UTC()
+	second := first.Add(time.Nanosecond)
+	if err := os.Mkdir(filepath.Join(workDir, fmt.Sprintf("run-%d", first.UnixNano())), 0o755); err != nil {
+		t.Fatalf("create existing run directory: %v", err)
+	}
+	restoreUTCNow := replaceUTCNow(func() func() time.Time {
+		calls := 0
+		return func() time.Time {
+			calls++
+			if calls == 1 {
+				return first
+			}
+			return second
+		}
+	}())
+	t.Cleanup(restoreUTCNow)
+
+	runDir, err := NewRunDirectory(workDir, RetentionAuto)
+	if err != nil {
+		t.Fatalf("NewRunDirectory: %v", err)
+	}
+
+	wantRunID := fmt.Sprintf("run-%d", second.UnixNano())
+	if runDir.RunID() != wantRunID {
+		t.Fatalf("RunID = %q, want %q", runDir.RunID(), wantRunID)
+	}
+	if _, err := os.Stat(runDir.Path()); err != nil {
+		t.Fatalf("stat run directory: %v", err)
+	}
+}
+
+func TestNewRunDirectoryReturnsErrorAfterRunIDCollisionsExhausted(t *testing.T) {
+	workDir := t.TempDir()
+	collisionTime := time.Unix(0, 200).UTC()
+	collisionPath := filepath.Join(workDir, fmt.Sprintf("run-%d", collisionTime.UnixNano()))
+	if err := os.Mkdir(collisionPath, 0o755); err != nil {
+		t.Fatalf("create existing run directory: %v", err)
+	}
+	restoreUTCNow := replaceUTCNow(func() time.Time {
+		return collisionTime
+	})
+	t.Cleanup(restoreUTCNow)
+
+	_, err := NewRunDirectory(workDir, RetentionAuto)
+	if err == nil || !strings.Contains(err.Error(), "exhausted unique run ID attempts") {
+		t.Fatalf("expected exhausted collision error, got %v", err)
+	}
+}
+
 func TestNewRunDirectoryUsesDefaultWorkDirectory(t *testing.T) {
 	runDir, err := NewRunDirectory("", RetentionAuto)
 	if err != nil {
@@ -252,6 +304,14 @@ func newTestRunDirectory(t *testing.T) *RunDirectory {
 	return runDir
 }
 
+func replaceUTCNow(replacement func() time.Time) func() {
+	original := utcNow
+	utcNow = replacement
+	return func() {
+		utcNow = original
+	}
+}
+
 func readArtifact(t *testing.T, runDir *RunDirectory, name string) []byte {
 	t.Helper()
 	data, err := os.ReadFile(filepath.Join(runDir.Path(), name))