Fix high CPU usage from notifications and add regression tests

- Fix auto-updating Text(date, style: .time) causing continuous SwiftUI updates
  by using static formatting with .formatted(date:time:)
- Fix notification popover keeping SwiftUI observers active when closed by
  clearing contentViewController on popover close and recreating on open
- Fix focus loss when notifications arrive while typing by only setting
  focus in NotificationsPage when the page is visible
- Make Update Pill and Update Logs debug-only features
- Add CPU regression tests: test_cpu_usage.py, test_cpu_notifications.py
- Add lint test for auto-updating Text patterns: test_lint_swiftui_patterns.py

tests/test_cpu_usage.py

@@ -0,0 +1,180 @@
+#!/usr/bin/env python3
+"""
+CPU usage test for cmuxterm.
+
+This test monitors cmuxterm's CPU usage during idle periods to catch
+performance regressions like runaway animations or continuous view updates.
+
+Run this test after launching cmuxterm:
+    python3 tests/test_cpu_usage.py
+
+The test will fail if:
+- CPU usage exceeds 15% during idle (no user interaction)
+- The sample shows suspicious patterns (continuous body.getter calls, animations)
+"""
+
+from __future__ import annotations
+
+import subprocess
+import sys
+import time
+import re
+from pathlib import Path
+from typing import List, Optional
+
+
+# Maximum acceptable CPU usage during idle (percentage)
+MAX_IDLE_CPU_PERCENT = 15.0
+
+# How long to wait for app to settle before measuring (seconds)
+SETTLE_TIME = 2.0
+
+# Duration to monitor CPU usage (seconds)
+MONITOR_DURATION = 3.0
+
+# Sampling interval for CPU checks (seconds)
+SAMPLE_INTERVAL = 0.5
+
+# Patterns that indicate performance issues in sample output
+SUSPICIOUS_PATTERNS = [
+    r"body\.getter.*\d{3,}",  # View body getter called 100+ times
+    r"repeatForever",  # Runaway animations
+    r"TimelineView.*animation.*\d{3,}",  # Unpaused timeline views
+]
+
+
+def get_cmuxterm_pid() -> Optional[int]:
+    """Get the PID of the running cmuxterm process."""
+    result = subprocess.run(
+        ["pgrep", "-f", r"cmuxterm\.app/Contents/MacOS/cmuxterm$"],
+        capture_output=True,
+        text=True,
+    )
+    if result.returncode != 0:
+        # Try DEV build
+        result = subprocess.run(
+            ["pgrep", "-f", r"cmuxterm DEV\.app/Contents/MacOS/cmuxterm"],
+            capture_output=True,
+            text=True,
+        )
+    if result.returncode != 0:
+        return None
+    pids = result.stdout.strip().split("\n")
+    return int(pids[0]) if pids and pids[0] else None
+
+
+def get_cpu_usage(pid: int) -> float:
+    """Get current CPU usage percentage for a process."""
+    result = subprocess.run(
+        ["ps", "-p", str(pid), "-o", "%cpu="],
+        capture_output=True,
+        text=True,
+    )
+    if result.returncode != 0:
+        return 0.0
+    try:
+        return float(result.stdout.strip())
+    except ValueError:
+        return 0.0
+
+
+def sample_process(pid: int, duration: int = 2) -> str:
+    """Sample a process and return the output."""
+    result = subprocess.run(
+        ["sample", str(pid), str(duration)],
+        capture_output=True,
+        text=True,
+    )
+    return result.stdout + result.stderr
+
+
+def check_sample_for_issues(sample_output: str) -> List[str]:
+    """Check sample output for suspicious patterns."""
+    issues = []
+    for pattern in SUSPICIOUS_PATTERNS:
+        if re.search(pattern, sample_output):
+            issues.append(f"Found suspicious pattern: {pattern}")
+    return issues
+
+
+def monitor_cpu_usage(pid: int, duration: float, interval: float) -> List[float]:
+    """Monitor CPU usage over a period and return all readings."""
+    readings = []
+    start = time.time()
+    while time.time() - start < duration:
+        cpu = get_cpu_usage(pid)
+        readings.append(cpu)
+        time.sleep(interval)
+    return readings
+
+
+def main():
+    print("=" * 60)
+    print("cmuxterm CPU Usage Test")
+    print("=" * 60)
+
+    # Find cmuxterm process
+    pid = get_cmuxterm_pid()
+    if pid is None:
+        print("\n❌ SKIP: cmuxterm is not running")
+        print("Start cmuxterm and run this test again.")
+        return 0  # Not a failure, just skip
+
+    print(f"\nFound cmuxterm process: PID {pid}")
+
+    # Wait for app to settle
+    print(f"Waiting {SETTLE_TIME}s for app to settle...")
+    time.sleep(SETTLE_TIME)
+
+    # Monitor CPU usage
+    print(f"Monitoring CPU usage for {MONITOR_DURATION}s...")
+    readings = monitor_cpu_usage(pid, MONITOR_DURATION, SAMPLE_INTERVAL)
+
+    avg_cpu = sum(readings) / len(readings) if readings else 0
+    max_cpu = max(readings) if readings else 0
+    min_cpu = min(readings) if readings else 0
+
+    print(f"\nCPU Usage Results:")
+    print(f"  Average: {avg_cpu:.1f}%")
+    print(f"  Max:     {max_cpu:.1f}%")
+    print(f"  Min:     {min_cpu:.1f}%")
+    print(f"  Samples: {len(readings)}")
+
+    # Check if CPU is too high
+    if avg_cpu > MAX_IDLE_CPU_PERCENT:
+        print(f"\n❌ FAIL: Average CPU ({avg_cpu:.1f}%) exceeds threshold ({MAX_IDLE_CPU_PERCENT}%)")
+
+        # Take a sample to diagnose
+        print("\nTaking process sample for diagnosis...")
+        sample_output = sample_process(pid, 2)
+
+        # Check for known issues
+        issues = check_sample_for_issues(sample_output)
+        if issues:
+            print("\nDiagnostic findings:")
+            for issue in issues:
+                print(f"  - {issue}")
+
+        # Save sample for debugging
+        sample_file = Path("/tmp/cmuxterm_cpu_test_sample.txt")
+        sample_file.write_text(sample_output)
+        print(f"\nFull sample saved to: {sample_file}")
+
+        # Show top functions from sample
+        print("\nTop functions in sample (look for .body.getter or Animation):")
+        lines = sample_output.split("\n")
+        relevant_lines = [
+            l for l in lines
+            if "cmuxterm" in l and ("body" in l or "Animation" in l or "Timer" in l)
+        ][:10]
+        for line in relevant_lines:
+            print(f"  {line.strip()[:100]}")
+
+        return 1
+
+    print(f"\n✅ PASS: CPU usage is within acceptable range")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())