feat: add wings_enabled input (mise-wings cache integration) (#454)

## Summary

Adds two new inputs that gate the mise-wings asset cache for tool
installs. Existing workflows are unaffected: default `wings_enabled:
false` is a no-op.

| Input | Default | Description |
|---|---|---|
| `wings_enabled` | `false` | Route tool-install URLs through the wings
cache when `true` |

## How it works

When `wings_enabled: true`, the action exports `MISE_WINGS_ENABLED=1`.
Authentication is **fully automatic** — mise itself owns the GHA OIDC →
wings session exchange. No `mise wings login` step in workflow YAML, no
long-lived secrets to rotate.

When mise (built with wings support — see
[jdx/mise#9458](https://github.com/jdx/mise/pull/9458)) sees
`MISE_WINGS_ENABLED=1` and detects the GHA OIDC env vars
(`ACTIONS_ID_TOKEN_REQUEST_URL` + `ACTIONS_ID_TOKEN_REQUEST_TOKEN`), it:

1. Fetches the runner's OIDC token, scoped to the wings deployment
audience
2. POSTs it to `https://api.<host>/auth` to mint a wings CI session JWT
3. Caches the JWT in-process for the rest of the workflow run
4. Transparently rewrites `registry.npmjs.org` / `github.com` /
`api.github.com` URLs to the corresponding wings cache subdomains and
attaches the JWT as a Bearer header

## Why opt-in (not opt-out)

The default-off posture is deliberate. Many workflows already declare
`permissions: id-token: write` for unrelated reasons (SLSA provenance,
AWS OIDC, Sigstore, npm provenance, etc.). If `wings_enabled` defaulted
to `true`, those workflows would silently send the runner's OIDC
identity claims to a third-party cache without explicit consent. Cursor
Bugbot HIGH + Greptile P1+security correctly flagged the previous
"default true" iteration of this PR as a privacy regression.

Explicit opt-in keeps the gate visible in the workflow YAML.

## Workflow requirements

```yaml
permissions:
  id-token: write   # required for OIDC

jobs:
  build:
    steps:
      - uses: jdx/mise-action@<sha>
        with:
          wings_enabled: true
```

The action emits a clear warning when `wings_enabled: true` but
`id-token: write` is missing — without that hint, the user would see
"wings configured but doing nothing" and have no clue why.

## Test plan

- [x] `npm run all` — format + lint + package, clean
- [x] `dist/index.js` rebuilt and contains the wings hook (greppable:
`MISE_WINGS_ENABLED`, `setupWings`)
- [ ] End-to-end: a workflow with `wings_enabled: true`, `permissions:
id-token: write`, an active wings subscription, and a recent enough
`mise` binary. The mise repo's own `docs.yml` will exercise this path
once [jdx/mise#9458](https://github.com/jdx/mise/pull/9458) is merged.
- [ ] Default-off path: a workflow without the `wings_enabled` input
behaves identically to today.

## Out of scope

- Older mise binaries will see `MISE_WINGS_ENABLED` and silently ignore
it (no wings client code) — that's intended; the action doesn't gate on
mise version.
- Self-hosted runners: `permissions: id-token: write` only does anything
on GitHub-hosted runners by default. Self-hosted runners need extra
config; the warning above is conservative enough for both cases.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Introduces an opt-in path that can cause OIDC-based authentication to
a third-party cache and alters tool download routing when enabled.
Default-off behavior limits impact, but misconfiguration could create
confusing cache bypass or unexpected network/token exchange behavior.
> 
> **Overview**
> Adds a new **experimental** `wings_enabled` action input (default
`false`) to opt workflows into the mise-wings asset cache by exporting
`MISE_WINGS_ENABLED=1`.
> 
> When enabled, the action now runs `setupWings()` early to set the env
var and warn if GitHub OIDC env vars are missing (i.e., `permissions:
id-token: write` not configured), while leaving existing/default
behavior unchanged.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
969042fe52. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

src/index.ts

@@ -54,6 +54,25 @@ async function run(): Promise<void> {
       core.setOutput('cache-hit', false)
     }
 
+    // Wings opt-in hook (experimental). When
+    // `wings_enabled: true` is set, this exports
+    // `MISE_WINGS_ENABLED=1` so subsequent `mise install`
+    // commands in this workflow route through the wings
+    // cache. Default `false` so workflows with
+    // `id-token: write` (used for SLSA / AWS-OIDC / Sigstore /
+    // etc.) don't silently send the runner's OIDC token to
+    // a third-party cache without explicit consent.
+    //
+    // Note: `setupMise` fetches the mise binary itself with
+    // `curl`, which doesn't go through mise's HTTP layer —
+    // the wings rewriter only kicks in once the resulting
+    // mise binary runs `mise install` and friends. Ordering
+    // here is irrelevant for binary acceleration; we just
+    // want the env var set before any `mise` subcommand
+    // runs. Greptile + Gemini both flagged the previous
+    // comment as overstating what the early call accelerates.
+    setupWings()
+
     const version = core.getInput('version')
     const fetchFromGitHub = core.getBooleanInput('fetch_from_github')
     await setupMise(version, fetchFromGitHub)
@@ -79,6 +98,49 @@ async function run(): Promise<void> {
   }
 }
 
+/**
+ * Opt in to mise-wings caching for this workflow run. When
+ * `wings_enabled: true`, exports `MISE_WINGS_ENABLED=1` so
+ * subsequent `mise install` commands route through the
+ * cache.
+ *
+ * Mise itself owns the OIDC → wings session exchange — when
+ * it sees `MISE_WINGS_ENABLED=1` and the GHA OIDC env vars
+ * (`ACTIONS_ID_TOKEN_REQUEST_URL` +
+ * `ACTIONS_ID_TOKEN_REQUEST_TOKEN`), it fetches the runner's
+ * OIDC token, exchanges it at the proxy's `POST /auth`
+ * route, and caches the resulting session JWT for the rest
+ * of the process.
+ *
+ * Pre-flight check: `id-token: write` permission must be
+ * declared at the workflow or job level for the OIDC env
+ * vars to be present. We log a warning when wings is
+ * enabled but the env vars are absent — without this hint,
+ * the user sees a transparent "wings configured but doing
+ * nothing" which is hard to debug.
+ */
+function setupWings(): void {
+  if (!core.getBooleanInput('wings_enabled')) {
+    return
+  }
+  core.exportVariable('MISE_WINGS_ENABLED', '1')
+  core.info(
+    "mise-wings: enabled. mise will exchange the runner's OIDC token for a wings session on first use."
+  )
+
+  const oidcUrl = process.env.ACTIONS_ID_TOKEN_REQUEST_URL
+  const oidcToken = process.env.ACTIONS_ID_TOKEN_REQUEST_TOKEN
+  if (!oidcUrl || !oidcToken) {
+    core.warning(
+      'mise-wings: GHA OIDC env vars are missing. Add ' +
+        '`permissions: id-token: write` at the workflow or job ' +
+        'level so the runner can mint OIDC tokens. Without this, ' +
+        'mise falls through to direct-origin fetches and the cache ' +
+        'is bypassed.'
+    )
+  }
+}
+
 async function exportMiseEnv(): Promise<void> {
   core.startGroup('Exporting mise environment variables')