Remove context.Background() usage in libs/filer (#4657)

## Summary
- Replace `context.Background()` with proper context propagation in the
workspace files readahead cache
- Add `ctx` field to cache struct, passed at construction time instead
of using `context.Background()` in worker goroutines and enqueue calls
- Update `NewReadOnlyWorkspaceFilesExtensionsClient` to accept a
`context.Context` parameter
- Simplify the two public constructors into direct implementations
instead of delegating to a shared private function

## Test plan
- [x] Unit tests pass for `libs/filer` and `bundle/config/mutator`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: pietern

bundle/config/mutator/configure_wsfs.go

@@ -51,7 +51,7 @@ func (m *configureWSFS) Apply(ctx context.Context, b *bundle.Bundle) diag.Diagno
 	// If so, swap out vfs.Path instance of the sync root with one that
 	// makes all Workspace File System interactions extension aware.
 	p, err := vfs.NewFilerPath(ctx, root, func(path string) (filer.Filer, error) {
-		return filer.NewReadOnlyWorkspaceFilesExtensionsClient(b.WorkspaceClient(), path)
+		return filer.NewReadOnlyWorkspaceFilesExtensionsClient(ctx, b.WorkspaceClient(), path)
 	})
 	if err != nil {
 		return diag.FromErr(err)

libs/filer/workspace_files_cache.go

@@ -182,8 +182,9 @@ type executable interface {
 // cache stores all entries for cacheable Workspace File System calls.
 // We care about caching only [ReadDir] and [Stat] calls.
 type cache struct {
-	f Filer
-	m sync.Mutex
+	f   Filer
+	ctx context.Context
+	m   sync.Mutex
 
 	readDir map[string]*readDirEntry
 	stat    map[string]*statEntry
@@ -195,17 +196,17 @@ type cache struct {
 	wg sync.WaitGroup
 }
 
-func newWorkspaceFilesReadaheadCache(f Filer) *cache {
+func newWorkspaceFilesReadaheadCache(ctx context.Context, f Filer) *cache {
 	c := &cache{
-		f: f,
+		f:   f,
+		ctx: ctx,
 
 		readDir: make(map[string]*readDirEntry),
 		stat:    make(map[string]*statEntry),
 
 		queue: make(chan executable, kMaxQueueSize),
 	}
 
-	ctx := context.Background()
 	for range kNumCacheWorkers {
 		c.wg.Add(1)
 		go c.work(ctx)
@@ -251,7 +252,7 @@ func (c *cache) completeReadDirForDir(name string, dirEntry fs.DirEntry) {
 	if _, ok := c.readDir[name]; !ok {
 		// Create a new cache entry and queue the operation.
 		e := newReadDirEntry(name)
-		err := c.enqueue(context.Background(), e)
+		err := c.enqueue(c.ctx, e)
 		if err != nil {
 			e.markError(err)
 		}
@@ -278,7 +279,7 @@ func (c *cache) completeReadDirForFile(name string, dirEntry fs.DirEntry) {
 		// This is the only (?) case where this implementation is tied to the workspace filer.
 
 		// Queue a [Stat] call for the file.
-		err := c.enqueue(context.Background(), e)
+		err := c.enqueue(c.ctx, e)
 		if err != nil {
 			e.markError(err)
 		}

libs/filer/workspace_files_cache_test.go

@@ -81,7 +81,7 @@ func TestWorkspaceFilesCache_ReadDirCache(t *testing.T) {
 	}
 
 	ctx := t.Context()
-	cache := newWorkspaceFilesReadaheadCache(f)
+	cache := newWorkspaceFilesReadaheadCache(ctx, f)
 	defer cache.Cleanup()
 
 	// First read dir should hit the filer, second should hit the cache.
@@ -122,7 +122,7 @@ func TestWorkspaceFilesCache_ReadDirCacheIsolation(t *testing.T) {
 	}
 
 	ctx := t.Context()
-	cache := newWorkspaceFilesReadaheadCache(f)
+	cache := newWorkspaceFilesReadaheadCache(ctx, f)
 	defer cache.Cleanup()
 
 	// First read dir should hit the filer, second should hit the cache.
@@ -153,7 +153,7 @@ func TestWorkspaceFilesCache_StatCache(t *testing.T) {
 	}
 
 	ctx := t.Context()
-	cache := newWorkspaceFilesReadaheadCache(f)
+	cache := newWorkspaceFilesReadaheadCache(ctx, f)
 	defer cache.Cleanup()
 
 	// First stat should hit the filer, second should hit the cache.
@@ -222,7 +222,7 @@ func TestWorkspaceFilesCache_ReadDirPopulatesStatCache(t *testing.T) {
 	}
 
 	ctx := t.Context()
-	cache := newWorkspaceFilesReadaheadCache(f)
+	cache := newWorkspaceFilesReadaheadCache(ctx, f)
 	defer cache.Cleanup()
 
 	// Issue read dir to populate the stat cache.
@@ -289,7 +289,7 @@ func TestWorkspaceFilesCache_ReadDirTriggersReadahead(t *testing.T) {
 	}
 
 	ctx := t.Context()
-	cache := newWorkspaceFilesReadaheadCache(f)
+	cache := newWorkspaceFilesReadaheadCache(ctx, f)
 	defer cache.Cleanup()
 
 	// Issue read dir to populate the stat cache.

libs/filer/workspace_files_extensions_client.go

@@ -166,30 +166,35 @@ func (e ReadOnlyError) Error() string {
 // errors for namespace clashes (e.g. a file and a notebook or a directory and a notebook).
 // Thus users of these methods should be careful to avoid such clashes.
 func NewWorkspaceFilesExtensionsClient(w *databricks.WorkspaceClient, root string) (Filer, error) {
-	return newWorkspaceFilesExtensionsClient(w, root, false)
-}
+	filer, err := NewWorkspaceFilesClient(w, root)
+	if err != nil {
+		return nil, err
+	}
+
+	return &WorkspaceFilesExtensionsClient{
+		workspaceClient: w,
 
-func NewReadOnlyWorkspaceFilesExtensionsClient(w *databricks.WorkspaceClient, root string) (Filer, error) {
-	return newWorkspaceFilesExtensionsClient(w, root, true)
+		wsfs:     filer,
+		root:     root,
+		readonly: false,
+	}, nil
 }
 
-func newWorkspaceFilesExtensionsClient(w *databricks.WorkspaceClient, root string, readonly bool) (Filer, error) {
+func NewReadOnlyWorkspaceFilesExtensionsClient(ctx context.Context, w *databricks.WorkspaceClient, root string) (Filer, error) {
 	filer, err := NewWorkspaceFilesClient(w, root)
 	if err != nil {
 		return nil, err
 	}
 
-	if readonly {
-		// Wrap in a readahead cache to avoid making unnecessary calls to the workspace.
-		filer = newWorkspaceFilesReadaheadCache(filer)
-	}
+	// Wrap in a readahead cache to avoid making unnecessary calls to the workspace.
+	filer = newWorkspaceFilesReadaheadCache(ctx, filer)
 
 	return &WorkspaceFilesExtensionsClient{
 		workspaceClient: w,
 
 		wsfs:     filer,
 		root:     root,
-		readonly: readonly,
+		readonly: true,
 	}, nil
 }