Constant PLUGIN_TIMEOUT_BUFFER_SECONDS

pub const PLUGIN_TIMEOUT_BUFFER_SECONDS: u64 = 4;

Extra seconds added to the Rust-side timeout so both Node.js timeout layers fire first. The timeout hierarchy for a plugin with timeout T is:

1. Handler (pool-executor.ts): T — structured TIMEOUT response
2. Worker-pool safety net: T + 2s — catches stuck workers
3. Rust backstop (this buffer): T + 4s — catches hung Node.js process