feat(calibrate): --delay countdown + messagebox warning before capture

Same fix as atm debug: desktop snapshot happens several seconds after user
confirms, giving time to alt-tab TradeStation to the foreground and get
rid of terminal/IDE windows covering it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/atm/calibrate.py

@@ -363,14 +363,21 @@ _COLOR_ORDER = [
 ]
 
 
-def run_calibration(out_dir: Path, screenshot: Path | None = None) -> Path:
+def run_calibration(
+    out_dir: Path,
+    screenshot: Path | None = None,
+    capture_delay: float = 3.0,
+) -> Path:
     """Launch the guided calibration wizard and return the saved config path.
 
     If *screenshot* is provided, use that image instead of live window capture
     (useful for dev/testing on non-Windows hosts).
+    *capture_delay* seconds countdown before the full-desktop snapshot — gives
+    the user time to bring TradeStation to the foreground and minimize anything
+    that covers it (PowerShell, VS Code, etc.).
     """
     import tkinter as tk
-    from tkinter import simpledialog
+    from tkinter import simpledialog, messagebox
     from PIL import Image
 
     out_dir = Path(out_dir)
@@ -407,6 +414,19 @@ def run_calibration(out_dir: Path, screenshot: Path | None = None) -> Path:
         # Default: region-select on full desktop (reliable with GPU-rendered apps).
         # Returns (cropped image, virtual-desktop region) so runtime capture can
         # re-crop the same area without needing pygetwindow to find the chart.
+        if capture_delay > 0:
+            root_msg = tk.Tk(); root_msg.withdraw()
+            messagebox.showinfo(
+                "Ready?",
+                f"Bring TradeStation to the foreground so it's FULLY VISIBLE.\n\n"
+                f"Minimize this terminal / VS Code / anything covering the chart.\n\n"
+                f"After you press OK, the desktop screenshot is taken in {capture_delay:.0f}s.",
+                parent=root_msg,
+            )
+            root_msg.destroy()
+            for i in range(int(capture_delay), 0, -1):
+                print(f"  capture in {i}...", flush=True)
+                time.sleep(1.0)
         try:
             pil_img, chart_region = _capture_fullscreen_region()
         except ValueError:

src/atm/main.py

@@ -35,6 +35,10 @@ def main(argv=None) -> None:
         "--screenshot", type=Path, default=None, metavar="PATH",
         help="Use a saved screenshot instead of live window capture (dev/testing)",
     )
+    p_cal.add_argument(
+        "--delay", type=float, default=3.0, metavar="SEC",
+        help="Countdown before desktop snapshot (bring TradeStation to front). Default 3.",
+    )
 
     # label
     p_label = sub.add_parser("label", help="Label dot-colour samples (Tk)")
@@ -103,7 +107,7 @@ def _cmd_calibrate(args) -> None:
         from atm.calibrate import run_calibration
     except ImportError as exc:
         sys.exit(f"calibrate module not available: {exc}")
-    run_calibration(Path("configs"), screenshot=args.screenshot)
+    run_calibration(Path("configs"), screenshot=args.screenshot, capture_delay=args.delay)
 
 
 def _cmd_label(args) -> None: