feat(run): --startup-delay + canary sanity check at startup

- 5s countdown before the loop starts so user can alt-tab TradeStation to
  the foreground and minimize whatever covers it.
- First frame triggers a canary phash check. Drift → WARN printed, clears
  auto-pause so user can Ctrl+C without the loop going silent. Canary
  status ('drift=X/Y' or 'capture_failed') is included in the startup
  ping so it's visible on Discord/Telegram.

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

src/atm/main.py

@@ -58,6 +58,10 @@ def main(argv=None) -> None:
         "--capture-stub", action="store_true",
         help="Use stub capture (reads PNGs from samples/); useful for smoke-testing on Linux",
     )
+    p_run.add_argument(
+        "--startup-delay", type=float, default=5.0, metavar="SEC",
+        help="Seconds to wait before the loop starts (bring TradeStation to front). Default 5.",
+    )
 
     # journal
     p_journal = sub.add_parser("journal", help="Add a trade journal entry interactively")
@@ -139,6 +143,15 @@ def _cmd_run(args) -> None:
     cfg = Config.load_current(Path("configs"))
     duration_s = args.duration * 3600 if args.duration is not None else None
     capture_stub = args.capture_stub or bool(os.environ.get("ATM_STUB_CAPTURE"))
+
+    delay = getattr(args, "startup_delay", 0.0)
+    if delay > 0 and not capture_stub:
+        print(f"Bring TradeStation to front, minimize PowerShell/VS Code. Starting in {delay:.0f}s...", flush=True)
+        for i in range(int(delay), 0, -1):
+            print(f"  {i}...", flush=True)
+            time.sleep(1.0)
+        print("RUN", flush=True)
+
     run_live(cfg, duration_s=duration_s, capture_stub=capture_stub)
 
 
@@ -282,15 +295,29 @@ def run_live(cfg, duration_s=None, capture_stub: bool = False) -> None:
     ]
     notifier = FanoutNotifier(backends, Path(cfg.dead_letter_path))
 
-    # Startup ping — confirms both channels work before the first bar closes.
+    # Sanity check: capture one frame, confirm canary matches calibration.
     from datetime import datetime
-    dur_note = f" duration={cfg.heartbeat_min:d}m heartbeat" if duration_s is None else f" duration={duration_s/3600:.2f}h"
+    first_frame = capture()
+    if first_frame is None:
+        print("WARN: first capture returned None — window/region missing", flush=True)
+        canary_status = "capture_failed"
+    else:
+        first_check = canary.check(first_frame)
+        canary_status = f"drift={first_check.distance}/{cfg.canary.drift_threshold}"
+        if first_check.drifted:
+            print(f"WARN: canary drift at startup ({canary_status}). Wrong window in front?", flush=True)
+            canary.resume()  # clear the auto-pause so user can Ctrl+C and fix
+
+    dur_note = f" dur=∞" if duration_s is None else f" dur={duration_s/3600:.2f}h"
     notifier.send(Alert(
         kind="heartbeat",
         title="ATM started",
-        body=f"config={cfg.config_version}{dur_note} at {datetime.now().isoformat(timespec='seconds')}",
+        body=(
+            f"cfg={cfg.config_version}{dur_note} @ {datetime.now().isoformat(timespec='seconds')}\n"
+            f"canary: {canary_status}"
+        ),
     ))
-    audit.log({"event": "started", "config": cfg.config_version})
+    audit.log({"event": "started", "config": cfg.config_version, "canary": canary_status})
 
     start = time.monotonic()
     heartbeat_due = start + cfg.heartbeat_min * 60