Fix potential crashes and unhandled exceptions in cli utility helpers (Batch 9)

[Ra229287]

This PR fixes bugs #266 to #270.

Packet

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    "title": "Potential unhandled crashes in cli utility helpers (Batch 9)",
    "actual_behavior": "Various CLI parameters, environment definitions, and helper outputs 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 _endpoint_url_for_policy",
      "Pass invalid types to _safe_codex_client_value",
      "Pass invalid types to validate_codex_config_value",
      "Pass invalid types to toml_string",
      "Pass invalid types to update_toml_top_level_scalars"
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    "affected_workflow": "CLI Utility life-cycle"
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  "proposed_fix": {
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