From 3e66127b94fdebd4a6d52f77f4361c83c3292c93 Mon Sep 17 00:00:00 2001
From: Eric Rakestraw <eric@rakestraw.us>
Date: Sun, 9 Aug 2026 01:41:37 +0000
Subject: [PATCH] Write durable outputs through confined file writer

---
 internal/cli/run.go         | 51 ++++---------------------------------
 internal/cli/run_id_test.go | 23 +++++++++++++++--
 2 files changed, 26 insertions(+), 48 deletions(-)

diff --git a/internal/cli/run.go b/internal/cli/run.go
index 00ecd7e..609b302 100644
--- a/internal/cli/run.go
+++ b/internal/cli/run.go
@@ -19,6 +19,7 @@ import (
 	"gitea.maximumdirect.net/eric/notarius/internal/core/artifacts"
 	"gitea.maximumdirect.net/eric/notarius/internal/core/config"
 	"gitea.maximumdirect.net/eric/notarius/internal/core/debugbundle"
+	"gitea.maximumdirect.net/eric/notarius/internal/core/fileio"
 	"gitea.maximumdirect.net/eric/notarius/internal/framework/checkpoint"
 	"gitea.maximumdirect.net/eric/notarius/internal/framework/chunkplan"
 	"gitea.maximumdirect.net/eric/notarius/internal/framework/contracts"
@@ -757,17 +758,10 @@ func configSource(configPath string) string {
 }
 
 func writeOutputFiles(runOutputDir string, files []contracts.OutputFile) error {
-	type outputTarget struct {
-		path string
-		file contracts.OutputFile
-	}
-	targets := make([]outputTarget, 0, len(files))
 	for _, file := range files {
-		targetPath, err := outputFilePath(runOutputDir, file.Name)
-		if err != nil {
+		if _, err := outputFilePath(runOutputDir, file.Name); err != nil {
 			return err
 		}
-		targets = append(targets, outputTarget{path: targetPath, file: file})
 	}
 
 	outputParent := filepath.Dir(runOutputDir)
@@ -780,12 +774,9 @@ func writeOutputFiles(runOutputDir string, files []contracts.OutputFile) error {
 		}
 		return fmt.Errorf("create output run directory %q: %w", runOutputDir, err)
 	}
-	for _, target := range targets {
-		if err := os.MkdirAll(filepath.Dir(target.path), 0o755); err != nil {
-			return fmt.Errorf("create output directory %q: %w", filepath.Dir(target.path), err)
-		}
-		if err := writeFileAtomic(target.path, target.file.Bytes, 0o644); err != nil {
-			return fmt.Errorf("write output file %q: %w", target.file.Name, err)
+	for _, file := range files {
+		if err := fileio.WriteBytes(runOutputDir, file.Name, file.Bytes, 0o755, 0o644); err != nil {
+			return fmt.Errorf("write output file %q: %w", file.Name, err)
 		}
 	}
 	return nil
@@ -828,38 +819,6 @@ func outputFilePath(runOutputDir, logicalName string) (string, error) {
 	return target, nil
 }
 
-func writeFileAtomic(path string, data []byte, perm os.FileMode) error {
-	dir := filepath.Dir(path)
-	temp, err := os.CreateTemp(dir, "."+filepath.Base(path)+".tmp-*")
-	if err != nil {
-		return err
-	}
-	tempPath := temp.Name()
-	removeTemp := true
-	defer func() {
-		if removeTemp {
-			_ = os.Remove(tempPath)
-		}
-	}()
-
-	if _, err := temp.Write(data); err != nil {
-		_ = temp.Close()
-		return err
-	}
-	if err := temp.Chmod(perm); err != nil {
-		_ = temp.Close()
-		return err
-	}
-	if err := temp.Close(); err != nil {
-		return err
-	}
-	if err := os.Rename(tempPath, path); err != nil {
-		return err
-	}
-	removeTemp = false
-	return nil
-}
-
 func reorderRunArgs(args []string) []string {
 	var flags []string
 	var positionals []string
diff --git a/internal/cli/run_id_test.go b/internal/cli/run_id_test.go
index a4c08bb..ae0f9d9 100644
--- a/internal/cli/run_id_test.go
+++ b/internal/cli/run_id_test.go
@@ -38,10 +38,29 @@ func TestWriteOutputFilesSupportsNestedLogicalPaths(t *testing.T) {
 	if err := writeOutputFiles(runPath, []contracts.OutputFile{{Name: "nested/result.json", Bytes: []byte("result")}}); err != nil {
 		t.Fatal(err)
 	}
-	data, err := os.ReadFile(filepath.Join(runPath, "nested", "result.json"))
+	resultPath := filepath.Join(runPath, "nested", "result.json")
+	data, err := os.ReadFile(resultPath)
 	if err != nil || string(data) != "result" {
 		t.Fatalf("nested output = %q, %v", data, err)
 	}
+	for path, want := range map[string]os.FileMode{runPath: 0o755, filepath.Join(runPath, "nested"): 0o755, resultPath: 0o644} {
+		info, err := os.Stat(path)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if info.Mode().Perm() != want {
+			t.Fatalf("%s mode = %#o, want %#o", path, info.Mode().Perm(), want)
+		}
+	}
+	entries, err := os.ReadDir(filepath.Join(runPath, "nested"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, entry := range entries {
+		if strings.Contains(entry.Name(), ".tmp-") {
+			t.Fatalf("temporary file remains: %s", entry.Name())
+		}
+	}
 }
 
 func TestWriteOutputFilesRejectsUnsafeNamesBeforeAllocatingRunDirectory(t *testing.T) {
@@ -75,7 +94,7 @@ func TestWriteOutputFilesRetainsNewPartialDirectoryAndPreservesSibling(t *testin
 		{Name: "blocked", Bytes: []byte("partial output")},
 		{Name: "blocked/nested.json", Bytes: []byte("unreachable")},
 	})
-	if err == nil || !strings.Contains(err.Error(), "create output directory") {
+	if err == nil || !strings.Contains(err.Error(), `write output file "blocked/nested.json"`) {
 		t.Fatalf("writeOutputFiles() error = %v, want later directory failure", err)
 	}
 	if got, err := os.ReadFile(filepath.Join(runPath, "blocked")); err != nil || string(got) != "partial output" {