Raise Rust coverage gate to 100 percent

[jooh]

Summary

• raise the Rust coverage gate from the 95% line threshold to zero uncovered lines
• add targeted tests across collection commands, runtime paths, configuration helpers, CLI helpers, and process runner behavior
• regenerate the upstream parity inventory after expanding the Rust coverage surface

Validation

• make rust-coverage
• make tests
• subagent review loop reported no P0/P1 findings across collections, runtime, and common/config/CLI/process-runner changes