diff --git a/pkg/tools/builtin/filesystem.go b/pkg/tools/builtin/filesystem.go
index 34e250a85..1423985e2 100644
--- a/pkg/tools/builtin/filesystem.go
+++ b/pkg/tools/builtin/filesystem.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io/fs"
 	"log/slog"
@@ -51,6 +52,9 @@ var (
 	_ tools.Instructable = (*FilesystemTool)(nil)
 )
 
+// allowAllPaths is a no-op path filter that permits every path.
+func allowAllPaths(_ string) error { return nil }
+
 type FileSystemOpt func(*FilesystemTool)
 
 func WithPostEditCommands(postEditCommands []PostEditConfig) FileSystemOpt {
@@ -375,11 +379,7 @@ func (t *FilesystemTool) shouldIgnorePath(path string) bool {
 	// Lazily initialize the gitignore matcher on first use
 	t.initGitignoreMatcher()
 
-	if t.repoMatcher != nil && t.repoMatcher.ShouldIgnore(path) {
-		return true
-	}
-
-	return false
+	return t.repoMatcher != nil && t.repoMatcher.ShouldIgnore(path)
 }
 
 // Handler implementations
@@ -387,11 +387,7 @@ func (t *FilesystemTool) shouldIgnorePath(path string) bool {
 func (t *FilesystemTool) handleDirectoryTree(ctx context.Context, args DirectoryTreeArgs) (*tools.ToolCallResult, error) {
 	resolvedPath := t.resolvePath(args.Path)
 
-	isPathAllowed := func(_ string) error {
-		return nil
-	}
-
-	tree, err := fsx.DirectoryTree(ctx, resolvedPath, isPathAllowed, t.shouldIgnorePath, maxFiles)
+	tree, err := fsx.DirectoryTree(ctx, resolvedPath, allowAllPaths, t.shouldIgnorePath, maxFiles)
 	if err != nil {
 		return tools.ResultError(fmt.Sprintf("Error building directory tree: %s", err)), nil
 	}
@@ -512,7 +508,7 @@ func (t *FilesystemTool) handleReadFile(_ context.Context, args ReadFileArgs) (*
 	info, err := os.Stat(resolvedPath)
 	if err != nil {
 		var errMsg string
-		if os.IsNotExist(err) {
+		if errors.Is(err, fs.ErrNotExist) {
 			errMsg = "not found"
 		} else {
 			errMsg = err.Error()
@@ -543,24 +539,22 @@ func (t *FilesystemTool) handleReadFile(_ context.Context, args ReadFileArgs) (*
 		}, nil
 	}
 
+	text := string(content)
+
 	return &tools.ToolCallResult{
-		Output: string(content),
+		Output: text,
 		Meta: ReadFileMeta{
-			LineCount: strings.Count(string(content), "\n") + 1,
+			LineCount: strings.Count(text, "\n") + 1,
 		},
 	}, nil
 }
 
 // readImageFile reads an image file and returns it as base64-encoded image content.
+// The caller must ensure the file exists (e.g. via os.Stat) before calling this method.
 func (t *FilesystemTool) readImageFile(resolvedPath, originalPath string) (*tools.ToolCallResult, error) {
 	data, err := os.ReadFile(resolvedPath)
 	if err != nil {
-		var errMsg string
-		if os.IsNotExist(err) {
-			errMsg = "not found"
-		} else {
-			errMsg = err.Error()
-		}
+		errMsg := err.Error()
 		return &tools.ToolCallResult{
 			Output:  errMsg,
 			IsError: true,
@@ -627,7 +621,7 @@ func (t *FilesystemTool) handleReadMultipleFiles(ctx context.Context, args ReadM
 		content, err := os.ReadFile(resolvedPath)
 		if err != nil {
 			errMsg := err.Error()
-			if os.IsNotExist(err) {
+			if errors.Is(err, fs.ErrNotExist) {
 				errMsg = "not found"
 			}
 			contents = append(contents, PathContent{
@@ -639,12 +633,13 @@ func (t *FilesystemTool) handleReadMultipleFiles(ctx context.Context, args ReadM
 			continue
 		}
 
+		text := string(content)
 		contents = append(contents, PathContent{
 			Path:    path,
-			Content: string(content),
+			Content: text,
 		})
-		entry.Content = string(content)
-		entry.LineCount = strings.Count(string(content), "\n") + 1
+		entry.Content = text
+		entry.LineCount = strings.Count(text, "\n") + 1
 		meta.Files = append(meta.Files, entry)
 	}