fix(#150): close residual TOCTOU with LimitedReader at docmap open

cmd/review-bot/validatedocmap.go

@@ -152,9 +152,26 @@ func runValidateDocmap(args []string) int {
 		return 2
 	}
 
-	// Parse docmap YAML using the resolved path — eliminates any TOCTOU race
-	// between validation and use.
-	cfg, err := review.ParseDocMapConfig(resolvedDocmap)
+	// Open and read the docmap with a LimitedReader — closes the residual TOCTOU
+	// window between the Lstat size check in validateDocmapPath and the file open
+	// here. The limit is maxDocmapBytes+1 so we can detect a file that grew past
+	// the cap after the stat without reading unbounded bytes.
+	f, err := os.Open(resolvedDocmap)
+	if err != nil {
+		fmt.Fprintf(errWriter, "Error: failed to open docmap %q: %v\n", *docmapFlag, err)
+		return 2
+	}
+	defer f.Close() // nolint:errcheck
+	docmapData, err := io.ReadAll(io.LimitReader(f, maxDocmapBytes+1))
+	if err != nil {
+		fmt.Fprintf(errWriter, "Error: failed to read docmap %q: %v\n", *docmapFlag, err)
+		return 2
+	}
+	if int64(len(docmapData)) > maxDocmapBytes {
+		fmt.Fprintf(errWriter, "Error: --docmap %q exceeded %d-byte limit after open\n", *docmapFlag, maxDocmapBytes)
+		return 2
+	}
+	cfg, err := review.ParseDocMapConfigContent(string(docmapData), *docmapFlag)
 	if err != nil {
 		fmt.Fprintf(errWriter, "Error: failed to parse docmap %q: %v\n", *docmapFlag, err)
 		return 2