🎨 Palette: Improve CLI error handling for invalid inputs

.Jules/palette.md

@@ -5,3 +5,7 @@
 ## 2025-02-28 - Structured CLI Reports
 **Learning:** Dense numerical data in CLI output is hard to parse. Using ASCII box-drawing characters and alignment to create a "dashboard" or "invoice" style summary significantly improves readability and perceived quality.
 **Action:** When summarizing simulation or batch job results, always format the final report as a structured table or box rather than a list of print statements.
+
+## 2025-03-01 - Defensive CLI Design
+**Learning:** Users often mistype arguments (e.g., negative numbers). Without validation, this leads to confusing output or crashes. Friendly error messages with actionable feedback are crucial for CLI usability.
+**Action:** Always implement explicit validation for CLI arguments and provide colored, clear error messages before starting any heavy processing.

.github/workflows/python-package.yml

@@ -21,7 +21,7 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v3
+      uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies

.github/workflows/stale.yml

@@ -18,7 +18,7 @@ jobs:
       pull-requests: write
 
     steps:
-    - uses: actions/stale@v5
+    - uses: actions/stale@v9
       with:
         repo-token: ${{ secrets.GITHUB_TOKEN }}
         stale-issue-message: 'Stale issue message'

bitcoin_trading_simulation.py

@@ -142,6 +142,19 @@ def countdown(quiet=False):
     if args.no_color:
         Colors.disable()
 
+    if args.days <= 0:
+        print(f"{Colors.FAIL}Error: --days must be a positive integer.{Colors.ENDC}")
+        sys.exit(1)
+    if args.initial_cash <= 0:
+        print(f"{Colors.FAIL}Error: --initial-cash must be a positive amount.{Colors.ENDC}")
+        sys.exit(1)
+    if args.initial_price <= 0:
+        print(f"{Colors.FAIL}Error: --initial-price must be a positive amount.{Colors.ENDC}")
+        sys.exit(1)
+    if args.volatility < 0:
+        print(f"{Colors.FAIL}Error: --volatility must be non-negative.{Colors.ENDC}")
+        sys.exit(1)
+
     # Simulate prices
     prices = simulate_bitcoin_prices(days=args.days, initial_price=args.initial_price, volatility=args.volatility)
 

test_cli_args.py

@@ -0,0 +1,31 @@
+import subprocess
+import sys
+
+
+def run_cli(args):
+    return subprocess.run(
+        [sys.executable, "bitcoin_trading_simulation.py"] + args,
+        capture_output=True,
+        text=True
+    )
+
+
+def test_negative_days_error():
+    """Negative days should fail with a helpful error message."""
+    result = run_cli(["--days", "-5", "--quiet"])
+    assert result.returncode == 1
+    assert "Error: --days must be a positive integer" in result.stdout
+
+
+def test_negative_cash_error():
+    """Negative cash should fail with a helpful error message."""
+    result = run_cli(["--initial-cash", "-100", "--quiet"])
+    assert result.returncode == 1
+    assert "Error: --initial-cash must be a positive amount" in result.stdout
+
+
+def test_negative_volatility_error():
+    """Negative volatility should fail with a helpful error message."""
+    result = run_cli(["--volatility", "-0.1", "--quiet"])
+    assert result.returncode == 1
+    assert "Error: --volatility must be non-negative" in result.stdout