Align worker container with runner ownership

Run the inference container with the host runner's UID/GID so it can
write the checkout and result bind mounts after all capabilities are
dropped. Set HOME to /tmp for writable CLI and package caches.

Cover the launcher identity and privilege settings with a stub Docker
executable.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: d63bcb34-3969-4d14-b422-33728176ec03

Author: cklin

.github/dependabot-automation/controller.test.cjs

@@ -1225,6 +1225,56 @@ test("rechecks provenance, labels, CI, and head immediately before merging", asy
   }
 });
 
+test(
+  "container worker uses runner identity and writable home without elevated capabilities",
+  { skip: process.platform === "win32" },
+  (t) => {
+    const workspace = temporaryWorkspace(t);
+    const trusted = path.join(
+      workspace,
+      "trusted/.github/dependabot-automation",
+    );
+    fs.mkdirSync(trusted, { recursive: true });
+    for (const name of ["task", "dependency", "bin"]) {
+      fs.mkdirSync(path.join(workspace, name));
+    }
+    for (const name of ["prompt.txt", "worker.cjs", "repair-protocol.cjs"]) {
+      fs.copyFileSync(path.join(__dirname, name), path.join(trusted, name));
+    }
+    const callsFile = path.join(workspace, "docker-calls.jsonl");
+    fs.writeFileSync(
+      path.join(workspace, "bin/docker"),
+      '#!/usr/bin/env node\nconst fs = require("node:fs");\nfs.appendFileSync(process.env.DOCKER_CALLS, JSON.stringify(process.argv.slice(2)) + "\\n");\n',
+      { mode: 0o755 },
+    );
+    execFileSync("bash", [path.join(__dirname, "run-worker.sh")], {
+      cwd: workspace,
+      env: {
+        ...process.env,
+        PATH: `${path.join(workspace, "bin")}${path.delimiter}${process.env.PATH}`,
+        DOCKER_CALLS: callsFile,
+        GITHUB_TOKEN: "test-token",
+      },
+    });
+    const calls = fs
+      .readFileSync(callsFile, "utf8")
+      .trim()
+      .split("\n")
+      .map((line) => JSON.parse(line));
+    assert.equal(calls.length, 2);
+    assert(!calls[0].includes("GITHUB_TOKEN"));
+    const worker = calls[1];
+    assert.equal(
+      worker[worker.indexOf("--user") + 1],
+      `${process.getuid()}:${process.getgid()}`,
+    );
+    assert(worker.includes("HOME=/tmp"));
+    assert(worker.includes("GITHUB_TOKEN"));
+    assert(worker.includes("--cap-drop=ALL"));
+    assert(worker.includes("--security-opt=no-new-privileges"));
+  },
+);
+
 test("worker collects tracked edits, new tests, and deletions", (t) => {
   const work = temporaryWorkspace(t);
   const git = (...args) =>

.github/dependabot-automation/run-worker.sh

@@ -10,8 +10,9 @@ docker run --rm \
   npm install --prefix /task/cli @github/copilot@1.0.104
 
 docker run --rm --init --cpus=2 --memory=6g \
+  --user "$(id -u):$(id -g)" \
   --cap-drop=ALL --security-opt=no-new-privileges \
-  -e GITHUB_TOKEN -e COPILOT_HOME=/tmp/copilot \
+  -e GITHUB_TOKEN -e HOME=/tmp -e COPILOT_HOME=/tmp/copilot \
   -e GIT_CONFIG_COUNT=1 -e GIT_CONFIG_KEY_0=safe.directory \
   -e GIT_CONFIG_VALUE_0=/work \
   -e PATH=/task/cli/node_modules/.bin:/usr/local/bin:/usr/bin:/bin \