fix(chroot): mount binaries overlay at /host/tmp/awf-runner-bin to avoid read-only /host/usr collision on ARC/DinD

containers/agent/entrypoint.sh

@@ -637,6 +637,20 @@ run_chroot_command() {
     fi
   fi
 
+  # When chroot.binariesSourcePath is configured, the firewall mounts the runner-bin
+  # overlay at /host/tmp/awf-runner-bin (inside chroot: /tmp/awf-runner-bin).
+  # Prepend it to AWF_HOST_PATH so the chrooted PATH resolves runner-installed binaries
+  # (e.g. copilot, claude) even when they are absent from /usr/local/bin in the staged
+  # host filesystem. This is the primary mechanism for ARC/DinD runners where the
+  # runner-installed binaries live on the runner's /tmp emptyDir, not in /usr.
+  if [ -d /host/tmp/awf-runner-bin ]; then
+    case ":${AWF_HOST_PATH:-$PATH}:" in
+      *":/tmp/awf-runner-bin:"*) ;;
+      *) export AWF_HOST_PATH="/tmp/awf-runner-bin:${AWF_HOST_PATH:-$PATH}" ;;
+    esac
+    echo "[entrypoint] Runner binaries overlay detected at /tmp/awf-runner-bin; prepended to PATH"
+  fi
+
   # Copy AWF CA certificate to chroot-accessible path for ssl-bump TLS trust.
   # NODE_EXTRA_CA_CERTS points to /usr/local/share/ca-certificates/awf-ca.crt which
   # is a Docker volume mount on the container's overlay filesystem. After chroot /host,
@@ -1031,7 +1045,7 @@ AWFEOF
       printf 'if ! command -v -- %s >/dev/null 2>&1; then\n' "${AWF_PREFLIGHT_BINARY}" >> "/host${SCRIPT_FILE}"
       printf '  echo "[entrypoint][ERROR] Required binary '"'"'%s'"'"' is not available inside AWF chroot." >&2\n' "${AWF_PREFLIGHT_BINARY}" >> "/host${SCRIPT_FILE}"
       printf '  echo "[entrypoint][ERROR] Ensure '"'"'%s'"'"' is installed on the runner and present in a PATH directory bind-mounted into /host." >&2\n' "${AWF_PREFLIGHT_BINARY}" >> "/host${SCRIPT_FILE}"
-      printf '  echo "[entrypoint][ERROR] Standard bind-mounted PATH directories: /usr/local/bin, /usr/bin, /bin, /opt." >&2\n' >> "/host${SCRIPT_FILE}"
+      printf '  echo "[entrypoint][ERROR] Standard bind-mounted PATH directories: /tmp/awf-runner-bin, /usr/local/bin, /usr/bin, /bin, /opt." >&2\n' >> "/host${SCRIPT_FILE}"
       printf '  exit 127\n' >> "/host${SCRIPT_FILE}"
       printf 'fi\n' >> "/host${SCRIPT_FILE}"
     else

src/services/agent-volumes-mounts.test.ts

@@ -89,7 +89,7 @@ describe('agent service', () => {
 
     expect(volumes).toContain('/daemon-root/tmp:/tmp:rw');
     expect(volumes).toContain('/daemon-root/usr:/host/usr:ro');
-    expect(volumes).toContain('/daemon-root/tmp/gh-aw/runner-bin:/host/usr/local/bin:ro');
+    expect(volumes).toContain('/daemon-root/tmp/gh-aw/runner-bin:/host/tmp/awf-runner-bin:ro');
     expect(volumes).toContain('/daemon-root/etc/passwd:/host/etc/passwd:ro');
     expect(volumes).toContain('/daemon-root/workspace:/host/workspace:ro');
     expect(volumes).toContain('/dev/null:/host/var/run/docker.sock:ro');
@@ -103,7 +103,7 @@ describe('agent service', () => {
     expect(volumes).not.toContain('/daemon-root/sys:/host/sys:ro');
   });
 
-  it('should mount chroot binaries source path over /host/usr/local/bin', () => {
+  it('should mount chroot binaries source path at /host/tmp/awf-runner-bin', () => {
     const configWithBinariesOverlay = {
       ...getConfig(),
       chrootBinariesSourcePath: '/tmp/gh-aw/runner-bin',
@@ -112,7 +112,10 @@ describe('agent service', () => {
     const volumes = result.services.agent.volumes as string[];
 
     expect(volumes).toContain('/usr:/host/usr:ro');
-    expect(volumes).toContain('/tmp/gh-aw/runner-bin:/host/usr/local/bin:ro');
+    // Binaries overlay uses /host/tmp/awf-runner-bin (not /host/usr/local/bin) so that
+    // Docker can always create the mount-point directory inside the writable /host/tmp.
+    expect(volumes).toContain('/tmp/gh-aw/runner-bin:/host/tmp/awf-runner-bin:ro');
+    expect(volumes).not.toContain('/tmp/gh-aw/runner-bin:/host/usr/local/bin:ro');
   });
 
   it('should normalize trailing slash in dockerHostPathPrefix', () => {
@@ -126,6 +129,33 @@ describe('agent service', () => {
     expect(volumes).toContain('/daemon-root/tmp:/tmp:rw');
   });
 
+  it('should mount binaries overlay at /host/tmp/awf-runner-bin when binariesSourcePath equals dockerHostPathPrefix', () => {
+    // Regression test for ARC/DinD collision: when binariesSourcePath equals
+    // dockerHostPathPrefix (both /tmp/gh-aw), the old target /host/usr/local/bin
+    // could not be created by Docker because /host/usr was already mounted read-only.
+    // The new target /host/tmp/awf-runner-bin sits under the writable /host/tmp mount
+    // so Docker can always create the subdirectory mount-point.
+    const sharedPrefix = '/tmp/gh-aw';
+    const configCollision = {
+      ...getConfig(),
+      dockerHostPathPrefix: sharedPrefix,
+      chrootBinariesSourcePath: sharedPrefix, // same value as prefix — the problematic case
+    };
+    const result = generateDockerCompose(configCollision, mockNetworkConfig);
+    const volumes = result.services.agent.volumes as string[];
+
+    // /host/usr is mounted read-only from the staged prefix
+    expect(volumes).toContain(`${sharedPrefix}/usr:/host/usr:ro`);
+
+    // Binaries overlay is at /host/tmp/awf-runner-bin — NOT nested under /host/usr:ro
+    // The source equals the prefix so applyHostPathPrefixToVolumes leaves it un-prefixed
+    expect(volumes).toContain(`${sharedPrefix}:/host/tmp/awf-runner-bin:ro`);
+
+    // Must NOT produce the old colliding mount that Docker could not set up
+    expect(volumes).not.toContain(`${sharedPrefix}:/host/usr/local/bin:ro`);
+    expect(volumes.some((v: string) => v.includes('/host/usr/local/bin'))).toBe(false);
+  });
+
   it('should auto-stage the ARC/DinD manual bootstrap files under a shared /tmp docker-host-path-prefix', () => {
     const originalPath = process.env.PATH;
     const sharedTmpPrefix = fs.mkdtempSync(path.join('/tmp', 'gh-aw-'));

src/services/agent-volumes/system-mounts.ts

@@ -26,7 +26,15 @@ export function buildSystemMounts(workspaceDir: string, chrootBinariesSourcePath
 
   const normalizedBinariesPath = normalizeChrootBinariesSourcePath(chrootBinariesSourcePath);
   if (normalizedBinariesPath) {
-    mounts.push(`${normalizedBinariesPath}:/host/usr/local/bin:ro`);
+    // Mount under /host/tmp/awf-runner-bin (not /host/usr/local/bin) so Docker can
+    // always create the mount-point directory. /host/usr is mounted read-only, so
+    // Docker cannot mkdir /host/usr/local/bin after that parent mount is applied —
+    // which fails in DinD/ARC setups where the staged /usr tree lacks local/bin.
+    // /host/tmp is mounted read-write (/tmp:/host/tmp:rw), so subdirectory creation
+    // always succeeds regardless of the host's staged /tmp content.
+    // entrypoint.sh detects /host/tmp/awf-runner-bin and adds /tmp/awf-runner-bin
+    // to the chroot PATH automatically.
+    mounts.push(`${normalizedBinariesPath}:/host/tmp/awf-runner-bin:ro`);
   }
 
   return mounts;