chore: add a simple AGENTS.md

This commit adds a simple AGENTS.md. This wasn't human-curated, just the
output of opencode's `/init` with Opus 4.5.

Author: fisherdarling

AGENTS.md

@@ -0,0 +1,20 @@
+# AGENTS.md
+
+## Build & Test Commands
+- Build: `cargo build`
+- Test all: `cargo test`
+- Test single: `cargo test <test_name>` or `cargo test --test <file> <test_name>`
+- Clippy: `cargo clippy --all-targets -- -D warnings -D unreachable_pub -D clippy::await_holding_lock -D clippy::clone_on_ref_ptr`
+- Format: `cargo fmt --all`
+- Lint fix: `./scripts/lint-fix.sh`
+- Feature check: `cargo hack check --feature-powerset --no-dev-deps --depth 1`
+
+## Code Style
+- Rust 2021 edition, use `rustfmt` defaults
+- Imports: group std, external crates, then internal modules; use `crate::` for internal imports
+- Types: prefer `Box<dyn Error + Send + Sync>` for generic errors; use `anyhow::Result` for bootstrap errors
+- Naming: snake_case for functions/variables, PascalCase for types, SCREAMING_SNAKE for constants
+- Errors: use `BootstrapResult<T>` (anyhow) for initialization, `Result<T>` (boxed error) for runtime
+- Docs: add `///` doc comments for public items; `#![warn(missing_docs)]` is enabled
+- Feature flags: wrap platform/optional code with `#[cfg(feature = "...")]`
+- No `openssl`/`openssl-sys` - use `boring`, `ring`, or `rustls` instead