From 9457694e4651576407de70e16ba0146106e8622b Mon Sep 17 00:00:00 2001
From: Virgil <virgil@lethean.io>
Date: Fri, 3 Apr 2026 23:41:36 +0000
Subject: [PATCH] feat(process): preserve runner result order

---
 runner.go      | 37 +++++++++++++++++++++++++++----------
 runner_test.go | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 10 deletions(-)

diff --git a/runner.go b/runner.go
index ed1de10..07ba97b 100644
--- a/runner.go
+++ b/runner.go
@@ -13,6 +13,9 @@ type Runner struct {
 	service *Service
 }
 
+// ErrRunnerNoService is returned when a runner was created without a service.
+var ErrRunnerNoService = coreerr.E("", "runner service is nil", nil)
+
 // NewRunner creates a runner for the given service.
 func NewRunner(svc *Service) *Runner {
 	return &Runner{service: svc}
@@ -68,20 +71,24 @@ func (r RunAllResult) Success() bool {
 
 // RunAll executes specs respecting dependencies, parallelising where possible.
 func (r *Runner) RunAll(ctx context.Context, specs []RunSpec) (*RunAllResult, error) {
+	if err := r.ensureService(); err != nil {
+		return nil, err
+	}
 	start := time.Now()
 
 	// Build dependency graph
 	specMap := make(map[string]RunSpec)
+	indexMap := make(map[string]int, len(specs))
 	for _, spec := range specs {
 		specMap[spec.Name] = spec
+		indexMap[spec.Name] = len(indexMap)
 	}
 
 	// Track completion
 	completed := make(map[string]*RunResult)
 	var completedMu sync.Mutex
 
-	results := make([]RunResult, 0, len(specs))
-	var resultsMu sync.Mutex
+	results := make([]RunResult, len(specs))
 
 	// Process specs in waves
 	remaining := make(map[string]RunSpec)
@@ -99,16 +106,15 @@ func (r *Runner) RunAll(ctx context.Context, specs []RunSpec) (*RunAllResult, er
 		}
 
 		if len(ready) == 0 && len(remaining) > 0 {
-			// Deadlock — circular dependency or missing specs. Report them as skipped
-			// with an error so callers can distinguish dependency graph issues from
-			// command execution failures.
+			// Deadlock - circular dependency or missing specs.
+			// Keep the output aligned with the input order.
 			for name := range remaining {
-				results = append(results, RunResult{
+				results[indexMap[name]] = RunResult{
 					Name:    name,
 					Spec:    remaining[name],
 					Skipped: true,
 					Error:   coreerr.E("Runner.RunAll", "circular dependency or missing dependency", nil),
-				})
+				}
 			}
 			break
 		}
@@ -149,9 +155,7 @@ func (r *Runner) RunAll(ctx context.Context, specs []RunSpec) (*RunAllResult, er
 				completed[spec.Name] = &result
 				completedMu.Unlock()
 
-				resultsMu.Lock()
-				results = append(results, result)
-				resultsMu.Unlock()
+				results[indexMap[spec.Name]] = result
 			}(spec)
 		}
 		wg.Wait()
@@ -181,6 +185,13 @@ func (r *Runner) RunAll(ctx context.Context, specs []RunSpec) (*RunAllResult, er
 	return aggResult, nil
 }
 
+func (r *Runner) ensureService() error {
+	if r == nil || r.service == nil {
+		return ErrRunnerNoService
+	}
+	return nil
+}
+
 // canRun checks if all dependencies are completed.
 func (r *Runner) canRun(spec RunSpec, completed map[string]*RunResult) bool {
 	for _, dep := range spec.After {
@@ -224,6 +235,9 @@ func (r *Runner) runSpec(ctx context.Context, spec RunSpec) RunResult {
 
 // RunSequential executes specs one after another, stopping on first failure.
 func (r *Runner) RunSequential(ctx context.Context, specs []RunSpec) (*RunAllResult, error) {
+	if err := r.ensureService(); err != nil {
+		return nil, err
+	}
 	start := time.Now()
 	results := make([]RunResult, 0, len(specs))
 
@@ -264,6 +278,9 @@ func (r *Runner) RunSequential(ctx context.Context, specs []RunSpec) (*RunAllRes
 
 // RunParallel executes all specs concurrently, regardless of dependencies.
 func (r *Runner) RunParallel(ctx context.Context, specs []RunSpec) (*RunAllResult, error) {
+	if err := r.ensureService(); err != nil {
+		return nil, err
+	}
 	start := time.Now()
 	results := make([]RunResult, len(specs))
 
diff --git a/runner_test.go b/runner_test.go
index cc4afd0..746c705 100644
--- a/runner_test.go
+++ b/runner_test.go
@@ -148,6 +148,24 @@ func TestRunner_RunAll(t *testing.T) {
 		assert.True(t, result.Success())
 		assert.Equal(t, 4, result.Passed)
 	})
+
+	t.Run("preserves input order", func(t *testing.T) {
+		runner := newTestRunner(t)
+
+		specs := []RunSpec{
+			{Name: "third", Command: "echo", Args: []string{"3"}, After: []string{"second"}},
+			{Name: "first", Command: "echo", Args: []string{"1"}},
+			{Name: "second", Command: "echo", Args: []string{"2"}, After: []string{"first"}},
+		}
+
+		result, err := runner.RunAll(context.Background(), specs)
+		require.NoError(t, err)
+
+		require.Len(t, result.Results, len(specs))
+		for i, res := range result.Results {
+			assert.Equal(t, specs[i].Name, res.Name)
+		}
+	})
 }
 
 func TestRunner_RunAll_CircularDeps(t *testing.T) {
@@ -207,3 +225,19 @@ func TestRunResult_Passed(t *testing.T) {
 		assert.False(t, r.Passed())
 	})
 }
+
+func TestRunner_NilService(t *testing.T) {
+	runner := NewRunner(nil)
+
+	_, err := runner.RunAll(context.Background(), nil)
+	require.Error(t, err)
+	assert.ErrorIs(t, err, ErrRunnerNoService)
+
+	_, err = runner.RunSequential(context.Background(), nil)
+	require.Error(t, err)
+	assert.ErrorIs(t, err, ErrRunnerNoService)
+
+	_, err = runner.RunParallel(context.Background(), nil)
+	require.Error(t, err)
+	assert.ErrorIs(t, err, ErrRunnerNoService)
+}