[TE-5476] Thread context.Context through UploadToS3 for cancellation support

Add context.Context parameter to UploadToS3 and use
http.NewRequestWithContext so the S3 upload can be cancelled or timed
out externally. Also fixes tarball size output to use stderr instead of
stdout for consistency with all other status messages.

Author: gchan

internal/command/backfill_commit_metadata.go

@@ -227,7 +227,7 @@ func BackfillCommitMetadata(ctx context.Context, cfg *config.Config, runner git.
 			return fmt.Errorf("presigning upload: %w", err)
 		}
 		fmt.Fprintln(os.Stderr, "Uploading to S3...")
-		if err := upload.UploadToS3(tarPath, presigned.Form); err != nil {
+		if err := upload.UploadToS3(ctx, tarPath, presigned.Form); err != nil {
 			removeTarball = false
 			fmt.Fprintf(os.Stderr, "Tarball retained at %s\n", tarPath)
 			return fmt.Errorf("uploading to S3: %w", err)

internal/command/upload_commit_metadata.go

@@ -46,7 +46,7 @@ func UploadCommitMetadata(ctx context.Context, cfg *config.Config) error {
 
 	// 5. Upload to S3
 	fmt.Fprintln(os.Stderr, "Uploading to S3...")
-	if err := upload.UploadToS3(cfg.UploadFile, presigned.Form); err != nil {
+	if err := upload.UploadToS3(ctx, cfg.UploadFile, presigned.Form); err != nil {
 		return fmt.Errorf("uploading to S3: %w", err)
 	}
 

internal/upload/s3.go

@@ -2,6 +2,7 @@ package upload
 
 import (
 	"bytes"
+	"context"
 	"fmt"
 	"io"
 	"mime/multipart"
@@ -32,7 +33,7 @@ type PresignedUploadForm struct {
 //
 // The multipart body is buffered in memory so the HTTP client can set the
 // Content-Length header, which S3 requires for presigned POST uploads.
-func UploadToS3(filePath string, form PresignedUploadForm) error {
+func UploadToS3(ctx context.Context, filePath string, form PresignedUploadForm) error {
 	debug.Printf("Uploading %s to %s", filePath, form.URL)
 
 	var buf bytes.Buffer
@@ -71,7 +72,7 @@ func UploadToS3(filePath string, form PresignedUploadForm) error {
 		return fmt.Errorf("closing multipart writer: %w", err)
 	}
 
-	req, err := http.NewRequest(form.Method, form.URL, &buf)
+	req, err := http.NewRequestWithContext(ctx, form.Method, form.URL, &buf)
 	if err != nil {
 		return fmt.Errorf("creating upload request: %w", err)
 	}

internal/upload/s3_test.go

@@ -1,6 +1,7 @@
 package upload
 
 import (
+	"context"
 	"io"
 	"mime"
 	"mime/multipart"
@@ -66,7 +67,7 @@ func TestUploadToS3_SendsFormFields(t *testing.T) {
 		FileInput: "file",
 	}
 
-	if err := UploadToS3(tmpFile, form); err != nil {
+	if err := UploadToS3(context.Background(), tmpFile, form); err != nil {
 		t.Fatalf("UploadToS3 error: %v", err)
 	}
 
@@ -113,7 +114,7 @@ func TestUploadToS3_SendsFile(t *testing.T) {
 		FileInput: "file",
 	}
 
-	if err := UploadToS3(tmpFile, form); err != nil {
+	if err := UploadToS3(context.Background(), tmpFile, form); err != nil {
 		t.Fatalf("UploadToS3 error: %v", err)
 	}
 
@@ -160,7 +161,7 @@ func TestUploadToS3_FieldOrder(t *testing.T) {
 		FileInput: "file",
 	}
 
-	if err := UploadToS3(tmpFile, form); err != nil {
+	if err := UploadToS3(context.Background(), tmpFile, form); err != nil {
 		t.Fatalf("UploadToS3 error: %v", err)
 	}
 
@@ -196,7 +197,7 @@ func TestUploadToS3_ServerError(t *testing.T) {
 		FileInput: "file",
 	}
 
-	err := UploadToS3(tmpFile, form)
+	err := UploadToS3(context.Background(), tmpFile, form)
 	if err == nil {
 		t.Fatal("expected error, got nil")
 	}
@@ -218,7 +219,7 @@ func TestUploadToS3_FileNotFound(t *testing.T) {
 		FileInput: "file",
 	}
 
-	err := UploadToS3("/nonexistent/file.tar.gz", form)
+	err := UploadToS3(context.Background(), "/nonexistent/file.tar.gz", form)
 	if err == nil {
 		t.Fatal("expected error for missing file, got nil")
 	}