The Standard Library as Architecture

• Arc<T> makes configuration, workspace data, strings, syntax trees, and query outputs cheap snapshot values.
• Mutex/RwLock are confined to caches and VFS views that genuinely cross worker boundaries.
• PathBuf exists in project/VFS layers; semantic base-db uses opaque FileId, preventing filesystem leakage.
• Option<T> is fundamental because incomplete Rust syntax is ordinary IDE input.
• Result<T, E> represents operational failure; parser APIs instead return a tree plus an error list.
• Box<dyn FnOnce()> type-erases heterogeneous worker jobs.
• atomics count extant tasks and make lightweight revision/lifecycle observations.
• Command and child handles separate Cargo, rustfmt, flycheck, and proc macros from the analysis process.

The best lesson is negative capability: types make some dependencies impossible. The parser cannot query Salsa; semantic crates cannot discover paths; IDE return values do not leak syntax/HIR objects; only the binary crate serializes LSP.