chore: defensive checks added to keep v0.2 stable

CONTRIBUTING.md

@@ -156,6 +156,7 @@ TRYBUILD=overwrite cargo test -p capsec --test compile_tests
 - **Include tests.** New authority patterns need integration tests. New type-system features need compile-fail tests.
 - **Run `cargo capsec audit`** against the repo itself before submitting — capsec dogfoods its own tool.
 - **Keep the security model intact.** `Cap<P>` must remain unforgeable and `!Send`. `Permission` must remain sealed. `Cap::new()` must remain `pub(crate)`. Any change that weakens these guarantees needs discussion in an issue first.
+- **`#[must_use]` convention.** Any new function or method returning `Result<T, CapSecError>`, `Cap<P>`, `SendCap<P>`, or `CapRoot` must have `#[must_use]`. Exception: if the return type itself already carries `#[must_use]` (e.g., `Cap<P>` does), a bare `#[must_use]` on the function is redundant and clippy will flag it — skip it in that case. The goal: discarding a capability check or proof token should always produce a compiler warning.
 - **Update docs** if you change public API. The facade crate's `lib.rs` doc comments and crate READMEs should stay current.
 
 ## Context pattern and macros

crates/capsec-core/src/lib.rs

@@ -1,3 +1,6 @@
+#![deny(missing_docs)]
+#![deny(rustdoc::broken_intra_doc_links)]
+
 //! # capsec-core
 //!
 //! Zero-cost capability tokens and permission traits for compile-time

crates/capsec-std/src/lib.rs

@@ -1,3 +1,6 @@
+#![deny(missing_docs)]
+#![deny(rustdoc::broken_intra_doc_links)]
+
 //! # capsec-std
 //!
 //! Capability-gated wrappers around the Rust standard library.

crates/capsec-tokio/src/lib.rs

@@ -1,3 +1,6 @@
+#![deny(missing_docs)]
+#![deny(rustdoc::broken_intra_doc_links)]
+
 //! # capsec-tokio
 //!
 //! Async capability-gated wrappers for [tokio](https://tokio.rs/) — the async

crates/capsec/Cargo.toml

@@ -22,3 +22,9 @@ trybuild.workspace = true
 capsec-core.workspace = true
 capsec-tokio = { workspace = true, features = ["full"] }
 tokio = { version = "1", features = ["rt-multi-thread", "macros", "fs", "net", "process", "io-util"] }
+
+[lints.rust]
+missing_docs = "deny"
+
+[lints.rustdoc]
+broken_intra_doc_links = "deny"