[IMPROVEMENT] Fix overly broad exception handling and improve error patterns

[vaishnaviasawale]

🐛 Problem

The jhack codebase contains multiple instances of problematic error handling that can hide bugs, reduce debugging effectiveness, and in some cases create security issues.

🔍 Issue Analysis

Critical Issues Found:

1. Bare except: clauses (most dangerous):

   # ❌ In jhack/charm/provision.py:105
   except:  # noqa: E722
       pass
   
   # ❌ In jhack/utils/charm_rpc_dispatch.py:81,88  
   except:  # noqa
       logger.error("failed serializing...")

2. Overly broad Exception handling:

   # ❌ In jhack/helpers.py:69
   except Exception as e:
       logger.error(e, exc_info=True)
       return False

3. Missing exception chaining:

   # ❌ Context lost
   except StopIteration:
       raise FileNotFoundError(f"could not find...")

4. Poor logging practices:

   # ❌ F-strings in logging
   logger.error(f"Command {cmd} failed")

🎯 Impact

• Hidden bugs: Bare except: catches KeyboardInterrupt, SystemExit, etc.
• Poor debugging: Lost exception context makes issues hard to trace
• Security risk: Broad exception handling can mask security issues
• Inconsistent error reporting: Users get unclear error messages

🛠️ Proposed Solution

1. Replace bare except: with specific handling:

# ✅ Good
try:
    risky_operation()
except (OSError, subprocess.SubprocessError) as e:
    logger.warning("Expected error: %s", e)
except Exception as e:
    logger.error("Unexpected error: %s", e, exc_info=True)
    raise

2. Add proper exception chaining:

# ✅ Good  
except StopIteration as exc:
    raise FileNotFoundError(f"could not find...") from exc

3. Use lazy logging:

# ✅ Good
logger.error("Command %s failed with code %d", cmd, returncode)

4. Specify encoding for file operations:

# ✅ Good
Path(file).write_text(content, encoding='utf-8')

📋 Files Requiring Changes

Critical (bare except):

• jhack/charm/provision.py:105
• jhack/utils/charm_rpc_dispatch.py:81,88
• jhack/utils/tail_logs.py:147
• jhack/utils/event_recorder/recorder.py:82,98

High Priority:

• jhack/helpers.py - Multiple logging and exception issues
• Various files with f-string logging and missing exception chaining

🧪 Implementation Steps

1. Phase 1: Fix bare except: clauses (security critical)
2. Phase 2: Add exception chaining and specific exception types
3. Phase 3: Convert logging to lazy formatting
4. Phase 4: Add encoding specifications and resource management

✅ Acceptance Criteria

• Zero bare except: clauses in codebase
• All custom exceptions use from chaining
• All logging uses lazy formatting (%s instead of f-strings)
• File operations specify encoding
• Linting rules prevent regression
• No functional regressions

🔧 Testing

def test_error_handling():
    """Verify proper error handling for edge cases."""
    # Test missing commands
    assert not check_command_available("nonexistent_cmd")
    
    # Test network failures  
    with patch('subprocess.run', side_effect=OSError):
        with pytest.raises(GetStatusError):
            juju_status()

📚 Additional Context

This addresses technical debt that impacts:

• Developer experience: Better error messages and debugging
• Code maintainability: Clear error handling patterns
• Security posture: Prevents masking of security issues
• User experience: More informative error messages

Priority: High (affects stability and security)
Effort: Medium (systematic changes, but well-defined)
Risk: Low (improvements don't change functionality)