rust-core-async-runtime

Conceptual overview of how async Rust works at the runtime level: the Future trait, the executor that polls it, the waker contract, Send rules across .await, and the choice of runtime crate. This skill teaches the mental model; mechanics live in cross-referenced skills.

Cross-references: [[rust-syntax-async-await]] [[rust-impl-async-tokio]] [[rust-core-memory-model]]

When to use this skill

User asks "what is Future / .await / Poll / a waker in Rust"
User asks "which async runtime should I pick" (tokio vs async-std vs smol vs embassy)
User asks "why is my async function not running" or "why does my future never complete"
User hits a Send error on tokio::spawn and needs to understand the rule, not just the fix
User asks "what is Pin / Unpin at a high level" (deep mechanics live in [[rust-syntax-async-await]] references/pinning.md)
User confuses async with parallel execution (it is not parallelism by itself)
User asks about structured concurrency, JoinSet, abort-on-drop semantics

For exact syntax of async fn / .await / async || and the keyword-level mechanics, refer the user to [[rust-syntax-async-await]]. For tokio-specific patterns (#[tokio::main], spawn_blocking, select!, channels), refer to [[rust-impl-async-tokio]].