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When adding a new IR instruction, you must touch a specific set of files. This skill describes each file, the pattern to follow, and important conventions.

Analyze per-commit binary size changes of the hermesvm shared library across a git commit range. Produces a markdown report with per-commit sizes and summary tables of significant increases and decreases.

Extract and manage error codes for React applications. Automatically extracts error messages from React source code and assigns unique error codes to new messages Detects "unknown error code" warnings and flags messages that need code assignment Validates that error codes remain synchronized with the current codebase through a simple yarn command

Manage React feature flags across channels, gate tests conditionally, and debug flag-specific test failures. Four flag files control defaults and channel-specific overrides (canary, www, React Native, test renderer) with __VARIANT__ flags simulating gatekeepers tested in both states Use @gate flagName pragma to skip tests entirely when a flag is unavailable, or inline gate() to branch assertions when behavior differs Adding a new flag requires entries in the main file plus all fork files;...

Automated code formatting and linting to resolve style issues before CI checks. Runs Prettier for code formatting and linc for lint validation in sequence Identifies remaining manual fixes needed after automated corrections Prevents CI failures by catching formatting and lint errors before commit

Inspect and compare feature flag states across React release channels. View all flags across channels (www, www-modern, canary, next, experimental, rn variants) or compare specific channels with --diff Output formats include default table view, CSV export, and cleanup status grouping Flag states indicated by symbols: enabled (✅), disabled (❌), variant testing (🧪), profiling-only (📊) Common pitfall: __VARIANT__ flags are tested in both states on www; use --diff to spot meaningful...

Static type checking for React code across DOM and native platforms. Four renderer options cover standard DOM, browser-specific code, React Native, and Fabric environments Run yarn flow with optional renderer argument; use yarn flow-ci for comprehensive but slower checks Reports type errors with file locations to help identify and fix issues quickly Watch for common pitfalls: missing renderer specification, unexamined $FlowFixMe suppressions, and incorrect type imports

For the full explanation and rationale, see doc/GCSafeCoding.md .

Use when needing to reorder, split, drop, or amend git commits that are not the top commit, without interactive editor access. Covers programmatic rebase via…

Relay is a GraphQL client for React that enforces colocated, composable, and type-safe data fetching. Its core insight is that each component should declare exactly what data it needs via GraphQL fragments, and Relay handles the rest — fetching, caching, consistency, and updates.

Run tests for React codebase across multiple release channels and configurations. Supports six release channels: source (default), experimental, www, www with variant false, stable, and classic, each with distinct feature flag configurations Accepts test patterns, watch mode for TDD, and variant flags to test different code paths Requires explicit test pattern argument to avoid running the entire test suite; uses --silent flag to surface failures and --no-watchman for sandboxing...

Pre-commit validation for React contributions with parallel type checking and testing. Runs formatting and linting sequentially, stopping on first failure to catch issues early Executes type checking and dual test suites (source and www) in parallel using subagents for efficiency Accepts optional test pattern argument to filter which tests run Provides detailed failure reporting with suggested fixes when any step fails