docs: add Cursor Cloud environment setup notes to AGENTS.md

AGENTS.md

@@ -448,3 +448,12 @@ Every outgoing HTTP request from `@workflow/world-vercel` to workflow-server (or
 Do **not** rely on ambient OpenTelemetry auto-instrumentation to do this: world-vercel's request paths use custom undici dispatchers / `global fetch`, which auto-instrumentation does not reliably hook. When you add a new request path or API version (e.g. a future v5 events API), wire the injection in the same place you build the request headers. The v4 events path (`fetchV4` in `events-v4.ts`) regressed cross-service correlation precisely by routing around `makeRequest` and skipping this step — workflow-server spans stopped joining the flow-route invocation trace until the injection was added back. Cover new paths with a test in `trace-propagation.test.ts`.
 
 The same rule covers a request path that is not an HTTP request. A non-`fetch` transport must still open the client span callers read a trace through: use `withHttpClientSpan` (`http-core.ts`), the envelope `instrumentedFetch` is built on, so the span carries the same name, kind and attributes rather than a hand-rolled parallel shape. The WS events transport is the worked example — `postEventFrameOverWs` synthesizes an `http POST` span per frame and tags it `workflow.events.transport: 'ws'`, and the handshake gets its own `workflow.events.ws.connect` span (`ws-transport-spans.test.ts`). Adding a transport that writes events without one silently deletes the per-event view of a run.
+
+## Cursor Cloud specific instructions
+
+The startup update script already runs `pnpm install --frozen-lockfile` (Node 22 and pnpm 10.20.0 are preinstalled), so dependencies are present when a session begins. A few non-obvious things about this repo's local dev loop:
+
+- **`pnpm build` (repo root) is required before running or e2e-testing any workbench app.** Workbenches consume the compiled `packages/*` output; a fresh checkout has none. The commands are already documented under "Development Commands" above — this note just flags that the first build is not optional.
+- **Building compiles a Rust→WASM artifact.** `@workflow/swc-plugin` (`packages/swc-plugin-workflow`) is built from Rust with `cargo build-wasm32`, and its `Cargo.toml` needs `edition2024` (Rust/Cargo ≥ 1.85). The environment snapshot ships a Rust `stable` toolchain (≥ 1.97) set as default plus the `wasm32-unknown-unknown` target, so `pnpm build` works out of the box; there is no committed prebuilt `.wasm`. If a build ever fails with `feature 'edition2024' is required`, the active Rust toolchain is too old — `rustup default stable && rustup target add wasm32-unknown-unknown`. The first `pnpm build` takes ~50s (mostly the Rust compile); it is turbo-cached afterward.
+- **Default backend is `world-local` (filesystem).** No Postgres, Docker, or Vercel credentials are needed for local dev or the HTTP e2e suite. Postgres/Vercel backends are opt-in via `WORKFLOW_TARGET_WORLD` (see "Core Package Testing" above).
+- **Primary runnable app for manual/e2e testing is `workbench/nextjs-turbopack`** (`WORKFLOW_PUBLIC_MANIFEST=1 pnpm dev`, port 3000). It exposes a UI at `/` that lists and triggers workflows, and HTTP trigger routes under `app/api/workflows/` (`start`, `await`). A quick smoke test: `POST /api/workflows/start` with `{"workflowName":"simple","args":[42]}` starts a run (id returned in the `x-workflow-run-id` header); `POST /api/workflows/await` with that `runId` returns `{"result":57}`.