meta: set up Cursor Cloud dev environment

.cursor/rules/cloud-environment.mdc

@@ -0,0 +1,56 @@
+---
+description: Cursor Cloud dev environment, build/test commands, and commit/PR workflow for the sentry-rust workspace
+alwaysApply: true
+---
+
+# Cursor Cloud environment & workflow
+
+This repo is the **Sentry SDK for Rust** — a Cargo workspace of library crates (`sentry`,
+`sentry-core`, `sentry-types`, and integration crates). There is no long-running server or
+GUI; the "applications" are the examples under `sentry/examples/` and `sentry-actix/examples/`.
+
+## Toolchain / environment (already provisioned by the update script + snapshot)
+- MSRV is **1.88** (`Cargo.toml` `rust-version`), so the default toolchain is Rust **stable**
+  (>= 1.88). The base image's older 1.83 toolchain is not sufficient — stable is installed and
+  set as default in the snapshot, with `rustfmt` and `clippy` components.
+- System libs `libssl-dev` and `pkg-config` are required (the `native-tls`/`openssl-sys` and
+  `curl` code paths pull in OpenSSL). These are baked into the snapshot. If a build fails with
+  "system library `openssl` was not found", reinstall with
+  `sudo apt-get install -y libssl-dev pkg-config`.
+
+## Standard commands (mirror CI in `.github/workflows/`)
+- Lint: `cargo fmt --all -- --check` and
+  `cargo clippy --all-features --workspace --tests --examples --locked -- -D clippy::all`
+- Build/check: `cargo check --all-features --locked`
+- Test: `cargo test --workspace --all-features --all-targets --locked` plus
+  `cargo test --workspace --all-features --doc --locked`
+- CI sets `RUSTFLAGS: -Dwarnings`; export it when reproducing CI locally.
+
+## Running an example (the "app")
+- `cargo run --example message-demo` runs, but with **no DSN the client is disabled** and no
+  event is transmitted (it just logs "initialized disabled sentry client").
+- To exercise the full capture → serialize → transport path, provide a DSN via the
+  `SENTRY_DSN` env var (read automatically by `sentry::init`), e.g. point it at a local mock
+  ingest server: `SENTRY_DSN="http://key@127.0.0.1:9999/42" cargo run --example message-demo`.
+  A real event envelope is then POSTed to `/api/<project_id>/envelope/`.
+
+## Pre-commit hooks
+- Always commit with pre-commit hooks enabled. `pre-commit` (the tool) is installed in the
+  snapshot and the repo's `commit-msg` hook is installed at `.git/hooks/commit-msg`.
+- Cursor sets `core.hooksPath` to its own dispatcher, which chains to the repo hooks in
+  `/workspace/.git/hooks`, so the pre-commit `commit-msg` hook runs alongside Cursor's hooks.
+- Because `core.hooksPath` is set, `pre-commit install` refuses to run directly. If the hook is
+  ever missing, reinstall with: `HP="$(git config --get core.hooksPath)"; git config --unset-all
+  core.hooksPath; pre-commit install --install-hooks; git config core.hooksPath "$HP"`.
+- The `commit-msg` hook runs `scripts/commit-msg-expand-issues.py`, which expands issue footers
+  like `Closes #123` into Markdown links (and Linear links) via `gh`. It is a no-op when the
+  message has no issue footer. Do NOT manually add Linear links — let the hook do it.
+
+## Commit messages & pull requests
+- Commit messages are reused as PR descriptions (see `.agents/skills/commit/SKILL.md`). Write
+  each commit's subject + body for human reviewers/maintainers.
+- When opening a PR, use the commit message as the PR **title and description** verbatim. Do
+  **not** use the `.github/pull_request_template.md` template.
+- Use Conventional Commits style for the subject (`feat:`, `fix:`, `ref:`, `meta:`, etc.).
+- Reference issues only via footers in the exact `Closes #123` / `Related to owner/repo#123`
+  format so the `commit-msg` hook can expand them.