Fix potential crashes and unhandled exceptions in subsystem helpers (Batch ext-29)

[Ra229287]

This PR fixes bugs #1040 to #1044.

Packet

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    "title": "Potential unhandled crashes in subsystem helpers (Batch ext-29)",
    "actual_behavior": "Various subsystem helper functions crashed with raw tracebacks when variables did not conform to expected formats.",
    "expected_behavior": "All helper functions should gracefully check parameter structures and parameter types, falling back to safe defaults without tracebacks.",
    "repro_steps": [
      "Pass invalid types to module_env_dir in src/spark_cli/sandbox/access.py",
      "Pass invalid types to read_env_file in src/spark_cli/sandbox/access.py",
      "Pass invalid types to write_env_file in src/spark_cli/sandbox/access.py",
      "Pass invalid types to level5_env_paths in src/spark_cli/sandbox/access.py",
      "Pass invalid types to persist_level5_guardrails in src/spark_cli/sandbox/access.py"
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    "affected_workflow": "CLI Subsystem lifecycle"
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  "proposed_fix": {
    "approach": "Added explicit type checks, try-except containment guards, and fallback initializers across 5 subsystem helper functions.",
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