Preserve validation cancellation during reader shutdown

internal/validation/tree.go

@@ -13,6 +13,7 @@ import (
 // CandidateTree is an inventory of one captured commit with blob contents
 // loaded lazily by object ID.
 type CandidateTree struct {
+	context        context.Context
 	repositoryDir  string
 	entries        []git.TreeEntry
 	byPath         map[string]int
@@ -24,13 +25,14 @@ type CandidateTree struct {
 }
 
 // ReadCandidateTree enumerates the captured commit without reading from the
-// worktree.
+// worktree. The supplied context also governs the scoped reader through closure.
 func ReadCandidateTree(ctx context.Context, repositoryDir, commit string) (*CandidateTree, error) {
 	entries, err := git.ReadTree(ctx, repositoryDir, commit)
 	if err != nil {
 		return nil, err
 	}
 	tree := &CandidateTree{
+		context:        ctx,
 		repositoryDir:  repositoryDir,
 		entries:        entries,
 		byPath:         make(map[string]int, len(entries)),
@@ -104,10 +106,12 @@ func (tree *CandidateTree) readBlob(ctx context.Context, entry git.TreeEntry) ([
 		return nil, fmt.Errorf("read committed path %q: candidate tree is closed", entry.Path)
 	}
 	if tree.blobReader == nil {
-		// The reader belongs to the tree and can outlive an individual read
-		// context. Each Read call still applies its own cancellation to the
-		// in-flight exchange.
-		tree.blobReader = git.NewBlobReader(context.Background(), tree.repositoryDir)
+		// The operation context governs shutdown independently of each read.
+		operationContext := tree.context
+		if operationContext == nil {
+			operationContext = context.Background()
+		}
+		tree.blobReader = git.NewBlobReader(operationContext, tree.repositoryDir)
 	}
 	contents, err := tree.blobReader.Read(ctx, entry.ObjectID)
 	if err != nil {