fix: harden diagnostics and smoke coverage

[wang135531]

Summary

• define a pilot terminal result contract for required process diagnostics
• classify completed runs as COMPLETE or PARTIAL based on top_node_processes
• harden Windows PowerShell JSON parsing and privacy-safe process output
• expand smoke coverage for Windows, Linux, malformed data and early exits

Validation

• python -B tests/smoke_test.py
• exit code 0
• final output: smoke tests passed