Method check_engine_pressure

nodedb/src/data/executor/core_loop/pressure.rs:43–75

Check engine-level memory pressure at the start of a write handler. - `Normal` / `Warning`: returns `None` — proceed normally. - `Critical`: increments the critical metric counter, returns `None` (handler proceeds; engine-specific flush is the handler's own responsibility — see timeseries ingest for the pattern). - `Emergency`: increments the emergency metric counter, returns `Some(Response)` wit

(
        &self,
        task: &ExecutionTask,
        engine: EngineId,
    )

    ///   `Some(Response)` with `ErrorCode::ResourcesExhausted`. The caller
    ///   must return this response immediately without executing the write.
    pub fn check_engine_pressure(
        &self,
        task: &ExecutionTask,
        engine: EngineId,
    ) -> Option<Response> {
        let governor = self.governor.as_ref()?;
        let pressure = governor.engine_pressure(engine);
        match pressure {
            PressureLevel::Normal | PressureLevel::Warning => None,
            PressureLevel::Critical => {
                if let Some(ref m) = self.metrics {
                    m.record_backpressure_critical(&engine.to_string());
                }
                warn!(
                    core = self.core_id,
                    engine = %engine,
                    "Critical memory pressure — proceeding with engine-specific flush"
                );
                None
            }
            PressureLevel::Emergency => {
                if let Some(ref m) = self.metrics {
                    m.record_backpressure_emergency(&engine.to_string());
                }
                warn!(
                    core = self.core_id,
                    engine = %engine,
                    "Emergency memory pressure — rejecting write with backpressure"
                );
                Some(self.response_error(task, ErrorCode::ResourcesExhausted))
            }
        }
    }

    /// Adjust SPSC read depth based on worst-case pressure across all engines.
    ///