Invalid config.toml is silently masked as a virtual default config instead of surfacing a parse error

[awsl233777]

Impact Scope

• CLI commands such as status and list
• Web/API state reads that rely on config-loading fallback behavior
• Troubleshooting and automation workflows that rely on accurate error reporting and exit codes

Reproduction Steps

1. Create a malformed config file:

   tmp=$(mktemp -d)
   mkdir -p "$tmp/.codex"
   cat > "$tmp/.codex/config.toml" <<'EOF2'
   model_provider = "openai"
   model = "gpt-5.3-codex"
   [model_providers.bad name]
   name = "bad name"
   EOF2

2. Run:

   HOME=$tmp USERPROFILE=$tmp node cli.js status
   HOME=$tmp USERPROFILE=$tmp node cli.js list

3. Observe the command output and exit code.

Expected Result

• The tool should clearly report that config.toml exists but is invalid.
• The parse error should be surfaced to the user.
• CLI exit code should be non-zero so scripts/CI can detect the failure.