git:20260828.1c9a1d2 to git:20260909.998370c

---

name: limrun-xcode-bazel

description: "Build a Bazel-based iOS / macOS / Apple app on Limrun's remote build execution (RBE) instead of a local Mac, and install it on a remote iOS simulator. Use when the project is a Bazel workspace (MODULE.bazel / WORKSPACE) building rules_apple / rules_swift targets and the user wants to `bazel build` it or run it on a simulator, or when a `--config=limrun` build or install misbehaves. To then tap, type, screenshot, or otherwise interact with the running app, use limrun-ios-simulator. For non-Bazel (plain xcodebuild) projects use limrun-xcode instead."

user-invocable: true

effort: high

---

# Bazel iOS builds on Limrun RBE

Build Bazel Apple projects on Limrun's remote Mac workers — from any environment

(Linux, Windows, macOS, VM, container), no local Xcode. `lim xcode rbe` brings up

a remote RBE stack, tunnels it to a local port, and writes a `.limrun/` config so

`bazelisk build --config=limrun` runs Apple actions remotely. Never fall back to

local Xcode or build tools.

## Auth and CLI

Install if needed: `npm install --global lim`. Auth is `lim login` or

`LIM_API_KEY` (may be set outside the project — don't ask for it just because

it's absent). The CLI is the source of truth: the commands in this skill are

verified, but if a flag errors or you need one not shown here, check

`lim xcode rbe --help` instead of guessing.

## Build

1. From the **Bazel workspace root** (has `MODULE.bazel` / `WORKSPACE`), run

`lim xcode rbe`. It sets up the instance + `.limrun/` config and **prints the

exact build command**. The tunnel runs in the background (prints a PID);

`--no-daemon` keeps it foreground.

2. Run the printed command, e.g.

`bazelisk --digest_function=sha256 build --config=limrun //App`.

To add your own Bazel flags to the limrun path without editing the generated

config, put them in **`user.limrun.bazelrc`** at the workspace root. The

generated config try-imports it last, so your `build:limrun --…` lines win, and

it survives `lim xcode rbe` regeneration (`.limrun/` does not).

## Run on a simulator

`lim xcode rbe` is build-only; attach a simulator when the user wants to see or

run the app. Check or attach (it installs the last build immediately, so no

rebuild is needed):

```bash

lim xcode get # is a simulator already attached?

lim ios create --attach # attach one

```

Add `--no-open` when you have no browser to show the user; it skips opening

the stream URL locally and still prints it for sharing.

If the attach output includes a signed stream URL, share it with the user as a

With a simulator attached, every successful `--config=limrun` build automatically

reinstalls and relaunches the app, no separate install step:

```bash

bazelisk --digest_function=sha256 build --config=limrun //App

```

Notes:

- **Attach upfront** if you already know you want a sim: `lim xcode rbe --ios`

(attaches at startup, removed on `--stop`).

- Auto-install happens server-side from the build's events; there is no

`lim xcode rbe install` subcommand or `--target` flag. To force a reinstall,

rebuild (a cache-hit rebuild is seconds).

- It fires when the successful invocation produced a single app, so in a

multi-app workspace build one app target per invocation (`//App`, not

`//...`); a multi-app build succeeds but installs nothing.

To tap, type, read the element tree, screenshot, or record the running app,

switch to the **`limrun-ios-simulator`** skill.

## Upload builds as assets

To publish a build as a Limrun asset (preview links, installing on other

simulators, CI artifacts), arm uploads at tunnel start or upload one build

after the fact:

```bash

lim xcode rbe --auto-upload preview/my-app --upload-ttl 24h # every successful build refreshes the asset

lim xcode rbe upload preview/my-app --ttl 24h # one-shot: the newest successful build

```

- `--auto-upload` holds for the tunnel's lifetime: each successful

`--config=limrun` build re-uploads the app under that asset name, no

post-build step. Upload results land in `.limrun/rbe.log`.

- `rbe upload` runs from the workspace root and needs a background tunnel

plus at least one successful build; it errors otherwise.

- TTLs are Go durations (`24h`, `30m`; `1d` is invalid) and optional; each

upload without one pushes the asset's expiry to 14 days from that upload.

- To change the `--auto-upload` config of a running tunnel, `--stop` and

re-run; the CLI refuses a mismatched re-arm instead of silently ignoring it.

- Preview an uploaded app in a browser at

`https://console.limrun.com/preview?asset=<name>&platform=ios`.

## Teardown

Stop with **`lim xcode rbe --stop`** (~20s to tear the remote stack down) and delete the instance with **`lim xcode delete <id>`**

## Gotchas

- **Always pass `--digest_function=sha256` before `build`** (use the command the

CLI prints verbatim). The Limrun cache is SHA256-only; Bazel 9 defaults to

BLAKE3. It's a startup flag, so it can't live in `--config=limrun`. Symptoms:

build → `Cannot use hash function BLAKE3 with remote cache`; install →

`non-SHA256 digest … rebuild with --digest_function=sha256`.

- **Run `lim xcode rbe` from the workspace root**, not a subdirectory — it writes

`.limrun/` there and fails fast otherwise.

- **A green build doesn't prove remote execution** — cache hits (`action cache

hit` / `remote cache hit`) make builds pass even with the tunnel gone. To force

and verify real remote execution, see `references/verify-remote.md`.

- **The printed `.ipa` path won't exist on your machine** — the build command

carries `--remote_download_outputs=minimal`, which keeps the artifact in the

instance's cache and downloads nothing. Bazel still prints its usual

`Target //App:App up-to-date: …/App.ipa` line, but that file is **not** on

disk. This is expected, not a failed build. With a simulator attached, the

build auto-installs from the artifact's cache digest (read from the build event

log, not the local file). Only if you genuinely need the `.ipa` locally, drop

`--remote_download_outputs=minimal` from the build command and Bazel downloads

the top-level output; auto-install keeps working either way.

- **A fresh instance can fail the first build with `Lost inputs no longer

available remotely`** (e.g. `… Assets.car`). It's a transient cache eviction

between instances, not a code error; Bazel prints `Found transient remote cache

error, retrying the build...` and the retry succeeds. To avoid hitting it

mid-demo, pre-warm with a full build right after `lim xcode rbe`.

- **`You don't have permission to save … in "CoreSimulator"`** (actool/ibtool) is

a fleet-side device gap, not your config. Retry; if it persists, report it to

Limrun.

- **The project's own Bazel settings can fight RBE** (Xcode pinned via a Starlark

transition, custom `remote_default_exec_properties`, sandbox-hostile genrules).

These are per-project, not Limrun bugs — walk

`references/project-compatibility.md` before concluding RBE is broken.