Move Docker Hub publishing to GAR mirror - #6033

The shared org-wide Docker Hub credentials previously fetched
from Vault have been disabled. Push k6 images to the GAR
staging repo using a short-lived, repo-scoped OIDC token;
the gar-image-mirror service copies them to docker.io/grafana
on our behalf.

- env.DOCKER_IMAGE_ID now points at
  us-docker.pkg.dev/grafanalabs-global/dockerhub-k6-prod-mirror/k6.
- The "Login to DockerHub" step is replaced with
  grafana/shared-workflows/actions/login-to-gar, which mints
  the GCP access token via Workload Identity Federation.
- GHCR publishing is unchanged.

Backport of #6033 to v1.x so v1 patch releases keep publishing
to docker.io/grafana/k6 after the shared credentials are removed.

k6 2.1.0

Created-by: HarmonybrewBot
Commit-by: HarmonybrewBot
Merged-by: HarmonybrewBot
Description: Created by `brew bump`

---

Created with `brew bump-formula-pr`.<details>
  <summary>release notes</summary>
  <pre>k6 `v2.1.0` is here 🎉  

This release includes:
- An opt-in feature-flag system — `--features`, the `K6_FEATURES` environment variable, and a `k6 features` discovery command — shipping with experimental native histograms for trend metrics as its first flag.
- A context-level `proxy` option for browser contexts.
- Subcommand discovery in `k6 x`, so binaries can report which extension commands they expose.

## Breaking changes

There are no breaking changes in this release.

## New features

### `k6 cloud test list` command [#6007](grafana/k6#6007)

A new `k6 cloud test` command group has been added, with a `k6 cloud test list` subcommand that lists the load tests of a Grafana Cloud k6 project. It complements the `k6 cloud project list` command introduced in v2.0.0.

The project to list tests for is resolved in the following order:

1. The `--project-id` flag.
2. The `K6_CLOUD_PROJECT_ID` environment variable (cloud config `projectID`).
3. The default project of the configured stack, populated by `k6 cloud login`.

Output defaults to a human-readable table. Pass `--json` to emit a JSON array instead, mirroring the format established by `k6 cloud project list`.

```shell
k6 cloud test list
k6 cloud test list --project-id 12345
k6 cloud test list --json
```

### Feature flags and experimental native histograms [#6055](grafana/k6#6055), [#6056](grafana/k6#6056)

k6 now has an opt-in feature-flag mechanism for trialing new, not-yet-stable behavior without affecting existing runs. Flags can be enabled on `k6 run` and `k6 cloud run` through the `--features` flag (comma-separated or repeated), the `K6_FEATURES` environment variable, or the `features` key in `config.json`. Enabled flags are surfaced as metric tags and propagated into archives and cloud workers so a run behaves consistently wherever it executes.

Use `k6 features` (or `k6 features --json`) to discover the available flags and their lifecycle:

```console
$ k6 features
FEATURE             LIFECYCLE      DESCRIPTION
native-histograms   Experimental   Use native histograms for trend metrics
```

The first flag shipped is `native-histograms`, an experimental flag that makes k6 use native histograms for trend metrics:

```shell
k6 run --features native-histograms script.js
# or
K6_FEATURES=native-histograms k6 run script.js
```

### Subcommand discovery in `k6 x` [#5972](grafana/k6#5972)

Running `k6 x` now lists the available subcommands — both the ones baked into the binary and those advertised by the extension registry (official and community). Tab-completion surfaces the same set once the catalog has been cached locally by a prior `k6 x` run, so completion never blocks on the network.

```text
$ k6 x
...
Available Commands:
  agent       Bootstrap an AI-assisted k6 testing workflow in any editor
  docs        CLI k6 docs for AI agents and users
  explore     Explore k6 extensions for Automatic Resolution
  mcp         An MCP server for k6 for AI agents
```

This makes a k6 binary self-describing — particularly useful for AI agents driving k6, which previously had no way to introspect which extension subcommands were available.

### Browser context proxy option [#5924](grafana/k6#5924)

Browser contexts can now be configured with a context-level `proxy` option, letting you route a context's traffic through a proxy without launching a custom-built binary or relying on environment proxy variables (which only affected k6's DevTools WebSocket connection). The option is wired to Chromium through `Target.createBrowserContext`, and invalid proxy configuration now fails early when `proxy.server` is missing. Thanks, @nightt5879!

```js
const context = await browser.newContext({
  proxy: {
    server: 'http://proxy.test:8080',
    bypass: 'localhost,127.0.0.1',
  },
});
```

### Browser `locator.isInViewport()` [#6023](grafana/k6#6023)

A new `locator.isInViewport()` method reports whether an element intersects the browser viewport. It accepts an optional `ratio` (0 to 1) that sets how much of the element must be visible, defaulting to `0` so any visible pixel counts, matching Playwright's `toBeInViewport` semantics. The call waits for the element to attach, honoring the `timeout` option, then measures the intersection once. Thanks, @Anuragp22!

```js
const button = page.locator('button#submit');
if (await button.isInViewport()) {
  await button.click();
}
```

### Basic auth for the OpenTelemetry HTTP exporter [#5997](grafana/k6#5997)

The OpenTelemetry output's HTTP exporter can now send HTTP Basic Auth credentials. Set them through the `K6_OTEL_HTTP_EXPORTER_USERNAME` and `K6_OTEL_HTTP_EXPORTER_PASSWORD` environment variables, or the `username` and `password` keys in the output config.

```shell
K6_OTEL_HTTP_EXPORTER_USERNAME=user \
K6_OTEL_HTTP_EXPORTER_PASSWORD=secret \
k6 run --out opentelemetry script.js
```

### `single()` selection helper in `k6/html` [#6002](grafana/k6#6002)

`Selection.single(selector)` returns at most one matching element, backed by goquery's `Single` matcher for a faster lookup than `find()` when you only need the first match. Thanks, @rohan-patnaik!

```js
import { parseHTML } from 'k6/html';

const doc = parseHTML(content);
const title = doc.single('h1').text();
```

## UX improvements and enhancements

- [#5971](grafana/k6#5971) Tags browser API failures with `module=browser` so that browser errors surfaced in Grafana Cloud Logs can be filtered separately from other log sources.

## Bug fixes

- [#5794](grafana/k6#5794) Makes the `--vus` flag work as a standalone execution shortcut instead of being silently ignored when a script defines scenarios. Running `k6 run script.js --vus N` now creates a `shared-iterations` scenario with `N` VUs and `N` iterations, overriding any script-defined scenarios with a warning — consistent with how `--iterations`, `--duration`, and `--stages` already behave. Thanks, @Reranko05!
- [#6013](grafana/k6#6013) Rejects invalid threshold percentiles. A percentile aggregation value outside the 0 to 100 range (or `NaN`) now fails parsing with a clear message instead of being silently accepted. Thanks, @immanuwell!
- [#6011](grafana/k6#6011) Writes the on-disk k6 config file with owner-only permissions (`0o600`, inside a `0o700` directory). The file can hold the Grafana Cloud API token (`collectors.cloud.token`), so tightening it keeps other local users on shared hosts (CI runners, multi-user boxes, sidecar containers) from reading the token. Existing configs are upgraded on the next write, for example the next `k6 cloud login`.

## Maintenance and internal improvements

- [#6033](grafana/k6#6033) Moves Docker Hub image publishing to a Google Artifact Registry mirror.
- [#5953](grafana/k6#5953) Installs `s3cmd` via `apt` instead of `pip` to fix the `k6packager` image build.
- [#6052](grafana/k6#6052) Fixes the browser end-to-end test workflow.
- [#5984](grafana/k6#5984) Routes per-test logger output to the test instance instead of the global `logrus`, improving test isolation.
- [#5985](grafana/k6#5985) Fixes the flaky `TestPageScreenshotFullpage` browser test.
- [#5981](grafana/k6#5981) Lets Renovate track the Go minor version in the `setup-go` workflows.
- [#5968](grafana/k6#5968) Honors the caller-pinned ref in the shared lint action.
- [#6041](grafana/k6#6041), [#6054](grafana/k6#6054) Aligns the Go module directive and toolchain (1.25.0 / 1.25.11).
- [#5967](grafana/k6#5967) Updates the release notes template after v2.0.0.
- [#6015](grafana/k6#6015) Updates `golang.org/x/net` to `v0.55.0` [security].
- [#6026](grafana/k6#6026) Updates `golang.org/x/crypto` to `v0.52.0` [security].
- [#5962](grafana/k6#5962), [#6028](grafana/k6#6028) Updates `google.golang.org/grpc` to `v1.81.1`.
- [#5960](grafana/k6#5960) Updates `grafana/shared-workflows/get-vault-secrets` to `v1.3.2`.
- [#5958](grafana/k6#5958) Updates `grafana/shared-workflows/azure-trusted-signing` to `v1.0.2`.
- [#5957](grafana/k6#5957) Updates `github/codeql-action` to `v4.35.4`.
- [#5959](grafana/k6#5959) Updates `grafana/shared-workflows/dockerhub-login` to `v1.0.4`.
- [#6009](grafana/k6#6009) Moves the browser `PageScreenshotOptions` parsing into the mapping layer.
- [#5964](grafana/k6#5964) Adds the k6 feature-flags specification under `openspec/`.
- [#6067](grafana/k6#6067) Forces the legacy `x/net/http2` implementation on the `gotip` CI test job.
- [#6065](grafana/k6#6065) Lets Renovate update the `Dockerfile` on the v1.x branch.
- [#6031](grafana/k6#6031) Updates `go.opentelemetry.io/otel` to `v1.44.0`.
- [#6086](grafana/k6#6086) Updates `golang.org/x` dependencies (`crypto` to `v0.53.0`, `net` to `v0.56.0`, `term` to `v0.44.0`).
- [#6061](grafana/k6#6061) Updates `golang.org/x/sync` to `v0.21.0`.
- [#6030](grafana/k6#6030) Updates `github.com/tidwall/gjson` to `v1.19.0`.
- [#6029](https:

See merge request: Harmonybrew/homebrew-core!13169