falcon-ocr-bucket: add --max-samples with early-termination scan

Mirrors pp-doclayout's --max-samples flag for falcon-ocr-bucket. When
set, discover_files() stops scanning once the limit is reached instead
of materializing-and-sorting the full directory tree first. Useful for
smoke tests and bounded slices on large mounted buckets.

Without --max-samples: full sorted list (deterministic, unchanged).
With --max-samples N: up to N files in filesystem-traversal order.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

falcon-ocr-bucket.py

@@ -64,14 +64,26 @@ def check_cuda_availability():
     logger.info(f"CUDA available. GPU: {torch.cuda.get_device_name(0)}")
 
 
-def discover_files(input_dir: Path) -> list[Path]:
+def discover_files(input_dir: Path, limit: int | None = None) -> list[Path]:
+    """Discover image and PDF files under input_dir.
+
+    Without `limit`, returns the full sorted list (deterministic order).
+    With `limit`, stops scanning once `limit` matching files are found
+    and returns them in filesystem order (much faster on huge mounted
+    buckets, but ordering is not deterministic).
+    """
     files = []
-    for path in sorted(input_dir.rglob("*")):
+    iterator = (
+        input_dir.rglob("*") if limit is not None else sorted(input_dir.rglob("*"))
+    )
+    for path in iterator:
         if not path.is_file():
             continue
         ext = path.suffix.lower()
         if ext in IMAGE_EXTENSIONS or ext == ".pdf":
             files.append(path)
+            if limit is not None and len(files) >= limit:
+                break
     return files
 
 
@@ -135,6 +147,13 @@ def main():
     parser.add_argument(
         "--no-cudagraph", action="store_true", help="Disable CUDA graph capture",
     )
+    parser.add_argument(
+        "--max-samples", type=int, default=None,
+        help="Limit number of input files to discover. Stops scanning early "
+             "once the limit is reached (much faster on large mounted buckets). "
+             "Applied before PDF page expansion. With --max-samples set, file "
+             "ordering is filesystem-dependent rather than sorted.",
+    )
     parser.add_argument(
         "--verbose", action="store_true", help="Print resolved package versions",
     )
@@ -155,8 +174,14 @@ def main():
     start_time = time.time()
 
     # Discover files
-    logger.info(f"Scanning {input_dir} for images and PDFs...")
-    files = discover_files(input_dir)
+    if args.max_samples is not None:
+        logger.info(
+            f"Scanning {input_dir} for up to {args.max_samples} images/PDFs "
+            f"(early termination, --max-samples)..."
+        )
+    else:
+        logger.info(f"Scanning {input_dir} for images and PDFs...")
+    files = discover_files(input_dir, limit=args.max_samples)
     if not files:
         logger.error(f"No image or PDF files found in {input_dir}")
         sys.exit(1)