Add disk space error handling utilities for better UX when disk is full

When disk space runs out, Claude Code can become unresponsive or crash without
clear feedback. This adds:

- New disk_space_utils.py module with:
  - ENOSPC error detection (errno 28)
  - User-friendly warning messages with remediation steps
  - Disk space availability checking
  - Safe file write/append helpers

- Updated security_reminder_hook.py to:
  - Check disk space at startup and warn users proactively
  - Detect disk space errors during state file operations
  - Provide actionable guidance when disk issues are detected

The warnings include specific remediation steps (df -h, cleaning /tmp,
emptying trash, docker prune) to help users resolve the issue.

Slack context: https://anthropic.slack.com/archives/C07VBSHV7EV/p1770941952212839

https://claude.ai/code/session_017ywHZBHvZasAWS6qcKXCb3

plugins/security-guidance/hooks/disk_space_utils.py

@@ -0,0 +1,173 @@
+#!/usr/bin/env python3
+"""
+Disk space utilities for Claude Code hooks.
+
+Provides helper functions to detect and handle disk space issues (ENOSPC errors)
+in a user-friendly manner.
+"""
+
+import errno
+import os
+import sys
+from typing import Optional, Tuple
+
+
+# ENOSPC errno value (28 on Linux/Mac)
+ENOSPC_ERRNO = errno.ENOSPC
+
+
+def is_disk_space_error(exception: Exception) -> bool:
+    """Check if an exception is related to disk space issues.
+
+    Args:
+        exception: The exception to check
+
+    Returns:
+        True if the exception indicates a disk space issue
+    """
+    # Check for OSError with ENOSPC errno
+    if isinstance(exception, OSError):
+        if hasattr(exception, 'errno') and exception.errno == ENOSPC_ERRNO:
+            return True
+        # Also check strerror for various disk space error messages
+        if hasattr(exception, 'strerror') and exception.strerror:
+            strerror_lower = exception.strerror.lower()
+            disk_space_indicators = [
+                'no space left on device',
+                'disk quota exceeded',
+                'not enough space',
+                'insufficient disk space',
+            ]
+            if any(indicator in strerror_lower for indicator in disk_space_indicators):
+                return True
+
+    # Check error message string as fallback
+    error_str = str(exception).lower()
+    if 'enospc' in error_str or 'no space left' in error_str:
+        return True
+
+    return False
+
+
+def get_disk_space_warning() -> str:
+    """Get a user-friendly warning message for disk space issues.
+
+    Returns:
+        Warning message string
+    """
+    return (
+        "WARNING: Disk space issue detected. Your disk may be full or nearly full.\n"
+        "This can cause Claude Code to become unresponsive or crash.\n"
+        "\n"
+        "Recommended actions:\n"
+        "  1. Free up disk space by deleting unnecessary files\n"
+        "  2. Check available space with: df -h\n"
+        "  3. Clean up temporary files: sudo rm -rf /tmp/* (use with caution)\n"
+        "  4. Empty trash/recycle bin\n"
+        "  5. Consider removing old Docker images: docker system prune"
+    )
+
+
+def check_available_disk_space(path: str = None, min_bytes: int = 10 * 1024 * 1024) -> Tuple[bool, Optional[str]]:
+    """Check if there's sufficient disk space available.
+
+    Args:
+        path: Path to check (defaults to home directory)
+        min_bytes: Minimum required bytes (default: 10MB)
+
+    Returns:
+        Tuple of (has_space, warning_message)
+        - has_space: True if sufficient space available
+        - warning_message: Warning string if low on space, None otherwise
+    """
+    if path is None:
+        path = os.path.expanduser("~")
+
+    try:
+        # Get disk usage statistics
+        stat = os.statvfs(path)
+        available_bytes = stat.f_frsize * stat.f_bavail
+
+        if available_bytes < min_bytes:
+            available_mb = available_bytes / (1024 * 1024)
+            required_mb = min_bytes / (1024 * 1024)
+            return False, (
+                f"Low disk space warning: Only {available_mb:.1f}MB available "
+                f"(recommended minimum: {required_mb:.1f}MB)\n"
+                f"{get_disk_space_warning()}"
+            )
+
+        return True, None
+
+    except (OSError, AttributeError):
+        # os.statvfs not available on all platforms (e.g., Windows)
+        # Return True and let actual write operations fail if there's no space
+        return True, None
+
+
+def safe_write_file(path: str, content: str, warn_on_disk_error: bool = True) -> Tuple[bool, Optional[str]]:
+    """Safely write content to a file with disk space error handling.
+
+    Args:
+        path: Path to write to
+        content: Content to write
+        warn_on_disk_error: If True, print warning to stderr on disk space errors
+
+    Returns:
+        Tuple of (success, error_message)
+        - success: True if write succeeded
+        - error_message: Error description if failed, None otherwise
+    """
+    try:
+        # Ensure directory exists
+        dir_path = os.path.dirname(path)
+        if dir_path:
+            os.makedirs(dir_path, exist_ok=True)
+
+        with open(path, 'w') as f:
+            f.write(content)
+
+        return True, None
+
+    except Exception as e:
+        if is_disk_space_error(e):
+            error_msg = f"Disk space error writing to {path}: {e}\n{get_disk_space_warning()}"
+            if warn_on_disk_error:
+                print(error_msg, file=sys.stderr)
+            return False, error_msg
+        else:
+            return False, f"Error writing to {path}: {e}"
+
+
+def safe_append_file(path: str, content: str, warn_on_disk_error: bool = True) -> Tuple[bool, Optional[str]]:
+    """Safely append content to a file with disk space error handling.
+
+    Args:
+        path: Path to append to
+        content: Content to append
+        warn_on_disk_error: If True, print warning to stderr on disk space errors
+
+    Returns:
+        Tuple of (success, error_message)
+        - success: True if append succeeded
+        - error_message: Error description if failed, None otherwise
+    """
+    try:
+        # Ensure directory exists
+        dir_path = os.path.dirname(path)
+        if dir_path:
+            os.makedirs(dir_path, exist_ok=True)
+
+        with open(path, 'a') as f:
+            f.write(content)
+
+        return True, None
+
+    except Exception as e:
+        if is_disk_space_error(e):
+            error_msg = f"Disk space error appending to {path}: {e}\n{get_disk_space_warning()}"
+            if warn_on_disk_error:
+                print(error_msg, file=sys.stderr)
+            return False, error_msg
+        else:
+            return False, f"Error appending to {path}: {e}"

plugins/security-guidance/hooks/security_reminder_hook.py

@@ -10,18 +10,40 @@ import random
 import sys
 from datetime import datetime
 
+# Import disk space utilities
+try:
+    from disk_space_utils import (
+        is_disk_space_error,
+        get_disk_space_warning,
+        check_available_disk_space,
+        safe_write_file,
+        safe_append_file,
+    )
+    DISK_UTILS_AVAILABLE = True
+except ImportError:
+    # Fallback if disk_space_utils not available
+    DISK_UTILS_AVAILABLE = False
+
 # Debug log file
 DEBUG_LOG_FILE = "/tmp/security-warnings-log.txt"
 
+# Track if we've already warned about disk space in this session
+_disk_space_warned = False
+
 
 def debug_log(message):
     """Append debug message to log file with timestamp."""
+    global _disk_space_warned
     try:
         timestamp = datetime.now().strftime("%Y-%m-%d %H:%M:%S.%f")[:-3]
         with open(DEBUG_LOG_FILE, "a") as f:
             f.write(f"[{timestamp}] {message}\n")
     except Exception as e:
-        # Silently ignore logging errors to avoid disrupting the hook
+        # Check if this is a disk space error and warn the user
+        if DISK_UTILS_AVAILABLE and is_disk_space_error(e) and not _disk_space_warned:
+            _disk_space_warned = True
+            print(f"[Security Hook] {get_disk_space_warning()}", file=sys.stderr)
+        # Continue silently to avoid disrupting the hook
         pass
 
 
@@ -158,26 +180,44 @@ def cleanup_old_state_files():
 
 def load_state(session_id):
     """Load the state of shown warnings from file."""
+    global _disk_space_warned
     state_file = get_state_file(session_id)
     if os.path.exists(state_file):
         try:
             with open(state_file, "r") as f:
                 return set(json.load(f))
-        except (json.JSONDecodeError, IOError):
+        except json.JSONDecodeError:
+            debug_log(f"JSON decode error reading state file: {state_file}")
+            return set()
+        except Exception as e:
+            # Check for disk-related errors (corrupted filesystem, etc.)
+            if DISK_UTILS_AVAILABLE and is_disk_space_error(e):
+                if not _disk_space_warned:
+                    _disk_space_warned = True
+                    print(f"[Security Hook] {get_disk_space_warning()}", file=sys.stderr)
+            debug_log(f"Error loading state file: {e}")
             return set()
     return set()
 
 
 def save_state(session_id, shown_warnings):
     """Save the state of shown warnings to file."""
+    global _disk_space_warned
     state_file = get_state_file(session_id)
     try:
         os.makedirs(os.path.dirname(state_file), exist_ok=True)
         with open(state_file, "w") as f:
             json.dump(list(shown_warnings), f)
-    except IOError as e:
+    except Exception as e:
+        # Check for disk space errors and provide user-friendly warning
+        if DISK_UTILS_AVAILABLE and is_disk_space_error(e):
+            if not _disk_space_warned:
+                _disk_space_warned = True
+                print(f"[Security Hook] {get_disk_space_warning()}", file=sys.stderr)
+            debug_log(f"Disk space error saving state file: {e}")
+        else:
             debug_log(f"Failed to save state file: {e}")
-        pass  # Fail silently if we can't save state
+        # Fail silently to not disrupt operation
 
 
 def check_patterns(file_path, content):
@@ -216,6 +256,8 @@ def extract_content_from_input(tool_name, tool_input):
 
 def main():
     """Main hook function."""
+    global _disk_space_warned
+
     # Check if security reminders are enabled
     security_reminder_enabled = os.environ.get("ENABLE_SECURITY_REMINDER", "1")
 
@@ -223,6 +265,13 @@ def main():
     if security_reminder_enabled == "0":
         sys.exit(0)
 
+    # Check for low disk space and warn user (only once per session)
+    if DISK_UTILS_AVAILABLE and not _disk_space_warned:
+        has_space, warning = check_available_disk_space()
+        if not has_space:
+            _disk_space_warned = True
+            print(f"[Security Hook] {warning}", file=sys.stderr)
+
     # Periodically clean up old state files (10% chance per run)
     if random.random() < 0.1:
         cleanup_old_state_files()