fix: stop the job's docker socket from becoming a directory (#1215)

Fixes https://gitea.com/gitea/runner/issues/1213

Fix the DooD regression that mounts `/var/run/docker.sock` as a directory. Keep the Docker proxy available through job and post steps. Clean stale resources before opening it, then remove containers before their networks and volumes during teardown.

Use a unique filesystem probe and preserve socket ownership. Fall back to direct access when proxying is unsupported. Preserve exec output and clean up active streams and failed starts.

Add a real Docker job test for mounted socket access, post steps and resource cleanup.

---------

Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1215
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: Zettat123 <zettat123@gmail.com>

act/runner/testdata/docker-proxy/action/action.yml

@@ -0,0 +1,6 @@
+name: docker-proxy
+description: Verify mounted Docker access through post steps
+runs:
+  using: node24
+  main: index.js
+  post: index.js

act/runner/testdata/docker-proxy/action/index.js

@@ -0,0 +1,53 @@
+const assert = require('node:assert/strict');
+const {once} = require('node:events');
+const fs = require('node:fs');
+const http = require('node:http');
+
+async function request(method, path, body) {
+  const req = http.request({
+    socketPath: '/var/run/docker.sock',
+    method,
+    path,
+    headers: {'Content-Type': 'application/json'},
+    signal: AbortSignal.timeout(10000),
+  });
+  req.end(JSON.stringify(body));
+  const [res] = await once(req, 'response');
+  req.on('error', (error) => res.destroy(error));
+  let data = '';
+  for await (const chunk of res.setEncoding('utf8')) {
+    data += chunk;
+  }
+  assert(res.statusCode >= 200 && res.statusCode < 300, `${method} ${path}: ${res.statusCode} ${data}`);
+  return data;
+}
+
+async function main() {
+  assert(fs.statSync('/var/run/docker.sock').isSocket(), 'Docker mount must be a socket');
+  assert.equal(await request('GET', '/_ping'), 'OK');
+  const api = `/v${JSON.parse(await request('GET', '/version')).ApiVersion}`;
+  const name = process.env.PROXY_TEST_RESOURCE;
+  const job = process.env.JOB_CONTAINER_NAME;
+  const post = process.env.STATE_post === 'true';
+  assert(name);
+  assert(job);
+  if (!post) {
+    await request('POST', `${api}/volumes/create`, {Name: name});
+    await request('POST', `${api}/networks/create`, {Name: name});
+    await request('POST', `${api}/networks/${name}/connect`, {Container: job});
+    fs.appendFileSync(process.env.GITHUB_STATE, 'post=true\n');
+  }
+  const label = process.env.PROXY_TEST_MODE === 'proxy' ? job : undefined;
+  assert.equal(JSON.parse(await request('GET', `${api}/volumes/${name}`)).Labels?.['com.gitea.runner.job'], label);
+  const network = JSON.parse(await request('GET', `${api}/networks/${name}`));
+  assert.equal(network.Labels?.['com.gitea.runner.job'], label);
+  assert(Object.values(network.Containers).some((container) => container.Name === job));
+  if (post) {
+    console.log('docker proxy post verified');
+  }
+}
+
+main().catch((error) => {
+  console.error(error);
+  process.exitCode = 1;
+});

act/runner/testdata/docker-proxy/push.yml

@@ -0,0 +1,8 @@
+name: docker-proxy
+on: push
+jobs:
+  proxy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./action