Enhanced FileTraversalEngine with ThreadPoolExecutor-based parallel processing, thread-safe progress tracking, binary detection via null-byte heuristic, auto-loaded .gitignore/.acmsignore exclusion patterns, and on-disk JSON cache persistence.

Includes 7 new Behave BDD scenarios for parallel indexing verification.

ISSUES CLOSED: #9981

@@ -0,0 +3,4 @@
+Validates that the parallel FileTraversalEngine correctly uses ThreadPoolExecutor
+to index large projects with multiple worker threads, while preserving thread safety
+and deterministic results.
+

@@ -11,1 +14,4 @@
 
+import json
+import os
+import threading

@@ -248,2 +327,4 @@
         return len(self.entries)
 
+    def to_json_dict(self) -> dict[str, Any]:
+        """Serialize the entire index to a JSON-serializable dictionary."""

@@ -278,0 +406,4 @@
+        self.progress = progress if progress is not None else IndexProgress()
+        # Normalize cache_path to a Path for atomic ops.
+        if isinstance(cache_path, str):
+            self.cache_path: Path | None = Path(cache_path)

@@ -0,0 +98,4 @@
+            f"# src module {i}\n", encoding="utf-8"
+        )
+    for i in range(pycache_entries):
+        (root / f"__pycache__" / f"module_{i:02d}.cpython-312.pyc").write_bytes(

@@ -0,0 +134,4 @@
+
+
+@given("a test directory with {count:d} Python files")
+def step_create_py_dir(context: Any, count: int) -> None:

@@ -10,2 +13,4 @@
 from __future__ import annotations
 
+import json
+import os

@@ -107,0 +122,4 @@
+    Thread-safe via a single lock protecting all counters.
+    """
+
+    _lock: threading.Lock = None  # type: ignore[assignment]

@@ -319,0 +539,4 @@
+        """
+        rel_str = str(file_path)
+        for pattern in exclude_patterns:
+            if pattern in rel_str:

@@ -402,2 +773,4 @@
         """Reset the index to empty state."""
         self.index = ACMSIndex()
+        # Reset progress tracker.
+        new_progress = IndexProgress()