x-dev-engineering

name	x-dev-engineering
description	Use this skill when implementing new features or debugging the core "For You" pipeline. The system has shifted from legacy heuristics toward a unified **Rust-based** pipeline powered by the **Phoenix** transformer (Grok).
metadata	{"author":"elemontcapital"}

X Development Engineering

Technical expertise for developing and extending the X recommendation engine, focusing on the Grok-powered Phoenix model, Rust candidate pipelines, and the removal of hand-engineered features.

Context

The modern X algorithm prioritizes a "No Hand-Engineered Features" philosophy. Relevance is learned directly from user engagement sequences using a transformer architecture.

For technical deep-dives, see:

• The Rust Candidate Pipeline
• Phoenix (Grok) Model Scoring
• Visibility & Safety Engineering

What it does

• Implements Grok-Native Components: Guidance on integrating with the Phoenix transformer for multi-action prediction (Like, Repost, Reply, etc.).
• Architects Candidate Sources: Logic for the two primary retrieval engines: Thunder (In-Network) and Phoenix Retrieval (Out-of-Network).
• Enforces Pipeline Order: Ensures components follow the strict sequence: Query Hydration -> Sourcing -> Hydration -> Pre-Scoring Filters -> Scoring -> Selection.
• Optimizes for Parallelism: Leverages Rust's async/await to execute independent hydration and sourcing tasks concurrently.

Guidelines

• Candidate Isolation: During scoring, ensure candidates cannot "attend" to each other in the transformer. This maintains score consistency and enables batching.
• No Heuristics: Avoid adding manual "if/then" rules for relevance; the Phoenix model should handle weightings through learned engagement probabilities.
• Hydration Efficiency: Fetch only necessary metadata (text, media, author status) during the Candidate Hydration stage after initial sourcing to minimize I/O.
• Safety First: All content must pass through VisibilityLib (Rust) for legal compliance and safety filtering before reaching the user.

Example Trigger Prompts

• "/gen-thrift new ranking signal"
• "/gen-thrift scaffold Rust Filter trait"
• "Add a new engagement signal to Phoenix prediction"
• "Show Rust implementation for Thunder candidate source"
• "Explain 'No Hand-Engineered Features' in ranking update"
• "How is candidate isolation applied in transformer attention?"

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