Preserve a writable /host$HOME under arc-dind sysroot staging

containers/agent/entrypoint.sh

@@ -333,9 +333,10 @@ if [ -n "$HTTP_PROXY" ]; then
 
   # Maven proxy config (~/.m2/settings.xml)
   # Only create if the file does not already exist, to avoid clobbering user-provided settings
-  mkdir -p "${JVM_HOME_PREFIX}/.m2"
-  if [ ! -f "${JVM_HOME_PREFIX}/.m2/settings.xml" ]; then
-    cat > "${JVM_HOME_PREFIX}/.m2/settings.xml" << MAVEN_EOF
+  if ! mkdir -p "${JVM_HOME_PREFIX}/.m2" 2>/dev/null || [ ! -w "${JVM_HOME_PREFIX}/.m2" ]; then
+    echo "[entrypoint] ⚠ Cannot write ${JVM_HOME_PREFIX}/.m2 (read-only home); skipping Maven proxy config"
+  elif [ ! -f "${JVM_HOME_PREFIX}/.m2/settings.xml" ]; then
+    if cat > "${JVM_HOME_PREFIX}/.m2/settings.xml" << MAVEN_EOF
 <settings>
   <proxies>
     <proxy>
@@ -355,25 +356,34 @@ if [ -n "$HTTP_PROXY" ]; then
   </proxies>
 </settings>
 MAVEN_EOF
-    chown awfuser:awfuser "${JVM_HOME_PREFIX}/.m2/settings.xml" 2>/dev/null || true
-    echo "[entrypoint] ✓ Created Maven proxy config (${JVM_HOME_PREFIX}/.m2/settings.xml)"
+    then
+      chown awfuser:awfuser "${JVM_HOME_PREFIX}/.m2/settings.xml" 2>/dev/null || true
+      echo "[entrypoint] ✓ Created Maven proxy config (${JVM_HOME_PREFIX}/.m2/settings.xml)"
+    else
+      echo "[entrypoint] ⚠ Failed to write ${JVM_HOME_PREFIX}/.m2/settings.xml; skipping Maven proxy config"
+    fi
   else
     echo "[entrypoint] ✓ Maven settings.xml already exists, skipping proxy config creation"
   fi
 
   # Gradle proxy config (~/.gradle/gradle.properties)
   # Only create if the file does not already exist, to avoid clobbering user-provided settings
   # (e.g., org.gradle.jvmargs, build cache settings, private repo credentials)
-  mkdir -p "${JVM_HOME_PREFIX}/.gradle"
-  if [ ! -f "${JVM_HOME_PREFIX}/.gradle/gradle.properties" ]; then
-    cat > "${JVM_HOME_PREFIX}/.gradle/gradle.properties" << GRADLE_EOF
+  if ! mkdir -p "${JVM_HOME_PREFIX}/.gradle" 2>/dev/null || [ ! -w "${JVM_HOME_PREFIX}/.gradle" ]; then
+    echo "[entrypoint] ⚠ Cannot write ${JVM_HOME_PREFIX}/.gradle (read-only home); skipping Gradle proxy config"
+  elif [ ! -f "${JVM_HOME_PREFIX}/.gradle/gradle.properties" ]; then
+    if cat > "${JVM_HOME_PREFIX}/.gradle/gradle.properties" << GRADLE_EOF
 systemProp.http.proxyHost=${PROXY_HOST}
 systemProp.http.proxyPort=${PROXY_PORT}
 systemProp.https.proxyHost=${PROXY_HOST}
 systemProp.https.proxyPort=${PROXY_PORT}
 GRADLE_EOF
-    chown awfuser:awfuser "${JVM_HOME_PREFIX}/.gradle/gradle.properties" 2>/dev/null || true
-    echo "[entrypoint] ✓ Created Gradle proxy config (${JVM_HOME_PREFIX}/.gradle/gradle.properties)"
+    then
+      chown awfuser:awfuser "${JVM_HOME_PREFIX}/.gradle/gradle.properties" 2>/dev/null || true
+      echo "[entrypoint] ✓ Created Gradle proxy config (${JVM_HOME_PREFIX}/.gradle/gradle.properties)"
+    else
+      echo "[entrypoint] ⚠ Failed to write ${JVM_HOME_PREFIX}/.gradle/gradle.properties; skipping Gradle proxy config"
+    fi
   else
     echo "[entrypoint] ✓ Gradle gradle.properties already exists, skipping proxy config creation"
   fi

docs/arc-dind.md

@@ -83,6 +83,31 @@ Language SDKs (Go, Node, Java, .NET) are NOT baked into the sysroot image. They
 - run: echo "RUNNER_TOOL_CACHE=/tmp/gh-aw/tool-cache" >> "$GITHUB_ENV"
 ```
 
+## Writable home under sysroot staging
+
+Sysroot staging drops agent bind mounts whose sources the DinD daemon cannot
+resolve, including AWF's own `${workDir}-chroot-home` volume for `/host$HOME`.
+An explicitly supplied mount is exempt from that filter: if the caller passes
+`--mount <daemon-visible-home>:$HOME:rw` (the gh-aw compiler does this for
+`${RUNNER_TEMP}/gh-aw/home`), the resulting `/host$HOME` mount is kept, because
+the caller vouches for the source being visible to the daemon. The exemption
+matches on both source and target, so AWF's own mounts to the same target stay
+subject to the filter.
+
+A writable `/host$HOME` matters for two reasons:
+
+- the `/dev/null` credential-hiding overlays are mounted under `/host$HOME`, and
+  runc cannot create those mountpoints under a read-only parent;
+- `entrypoint.sh` pre-seeds JVM build tool proxy config (`~/.m2`, `~/.gradle`)
+  under the chroot home.
+
+If no writable `/host$HOME` survives the filter, AWF logs a warning and skips
+the `/host$HOME` credential overlays instead of failing container creation — the
+overlays at the un-prefixed `$HOME` path (on the agent's own rootfs) are still
+applied, but credential files under the chroot home are not masked for that run.
+The entrypoint likewise warns and skips JVM proxy pre-seeding rather than
+aborting.
+
 ## What AWF handles automatically
 
 - Split-filesystem probing for `--docker-host-path-prefix`

src/compose-generator.test.ts

@@ -610,7 +610,7 @@ describe('generateDockerCompose', () => {
 
         generateDockerCompose(config, mockNetworkConfig);
 
-        expect(warnSpy).not.toHaveBeenCalled();
+        expect(warnSpy).not.toHaveBeenCalledWith(expect.stringContaining('under /opt'));
         warnSpy.mockRestore();
       });
 
@@ -650,7 +650,9 @@ describe('generateDockerCompose', () => {
         expect(homeTargets).toContain(`/host${workspaceDir}`);
         expect(homeTargets.some(target => target.startsWith(`/host${effectiveHomeForFilter}/.`))).toBe(false);
 
-        // Home root mounts (including trailing slash source) should be dropped.
+        // An explicitly supplied home-root mount (including trailing slash source)
+        // survives the filter: the caller vouches for its daemon visibility, and a
+        // writable /host$HOME is required by the credential overlays and entrypoint.
         const effectiveHome = getRealUserHome();
         const configWithHomeRootMount = {
           ...config,
@@ -661,7 +663,28 @@ describe('generateDockerCompose', () => {
           const target = v.split(':')[1];
           return target === `/host${effectiveHome}` || target === `/host${effectiveHome}/`;
         });
-        expect(homeRootMounts).toHaveLength(0);
+        expect(homeRootMounts).toEqual([`${effectiveHome}/:/host${effectiveHome}:rw`]);
+
+        // The chroot-home volume sourced from workDir is still dropped.
+        expect(
+          (resultWithHomeRootMount.services.agent.volumes as string[]).some(v =>
+            v.startsWith('/tmp/awf-12345-chroot-home'),
+          ),
+        ).toBe(false);
+
+        // Credential overlays under /host$HOME are kept when a writable home survives.
+        expect(
+          (resultWithHomeRootMount.services.agent.volumes as string[]).some(
+            v => v.startsWith('/dev/null:') && v.split(':')[1].startsWith(`/host${effectiveHome}/`),
+          ),
+        ).toBe(true);
+
+        // Without such a mount, those overlays are skipped (no writable parent exists).
+        expect(
+          volumes.some(
+            v => v.startsWith('/dev/null:') && v.split(':')[1].startsWith(`/host${effectiveHome}/`),
+          ),
+        ).toBe(false);
 
         // Should still have /tmp:/tmp, /sys, /dev, sysroot volume
         expect(volumes).toContain('/tmp:/tmp:rw');

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

@@ -189,4 +189,9 @@ describe('buildCustomVolumeMounts', () => {
     const result = buildCustomVolumeMounts(['/a:/b', '/c:/d:ro', 'named']);
     expect(result).toEqual(['/a:/host/b', '/c:/host/d:ro', 'named']);
   });
+
+  it('does not double-prefix targets that already start with /host', () => {
+    const result = buildCustomVolumeMounts(['/data:/host/data:ro', '/root:/host']);
+    expect(result).toEqual(['/data:/host/data:ro', '/root:/host']);
+  });
 });

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

@@ -92,12 +92,19 @@ function isExecutableFile(candidate: string): boolean {
 export function buildCustomVolumeMounts(
   volumeMounts?: string[],
   dockerHostPathPrefix?: string,
+  options: { quiet?: boolean } = {},
 ): string[] {
   if (!volumeMounts || volumeMounts.length === 0) {
     return [];
   }
 
-  logger.debug(`Adding ${volumeMounts.length} custom volume mount(s)`);
+  // `quiet` is used by callers that only re-derive the transformed specs for
+  // comparison (e.g. the sysroot volume filter) and must not log them twice.
+  const debug = (message: string) => {
+    if (!options.quiet) logger.debug(message);
+  };
+
+  debug(`Adding ${volumeMounts.length} custom volume mount(s)`);
 
   // Custom mount sources always use the runner's filesystem view. Translate
   // them even when a source already starts with the daemon-side prefix; this
@@ -114,11 +121,17 @@ export function buildCustomVolumeMounts(
       const hostPath = parts[0];
       const containerPath = parts[1];
       const mode = parts[2] || '';
-      const chrootContainerPath = `/host${containerPath}`;
+      // Targets that already carry the chroot prefix (some callers emit both an
+      // un-prefixed and a `/host`-prefixed mount) must not be prefixed again,
+      // otherwise they land at `/host/host/…` and mount nothing meaningful.
+      const chrootContainerPath =
+        containerPath === '/host' || containerPath.startsWith('/host/')
+          ? containerPath
+          : `/host${containerPath}`;
       const transformedMount = mode
         ? `${hostPath}:${chrootContainerPath}:${mode}`
         : `${hostPath}:${chrootContainerPath}`;
-      logger.debug(`Adding custom volume mount: ${volumeMounts[index]} -> ${transformedMount} (chroot-adjusted)`);
+      debug(`Adding custom volume mount: ${volumeMounts[index]} -> ${transformedMount} (chroot-adjusted)`);
       return transformedMount;
     }
 

src/services/optional-services.test.ts

@@ -63,6 +63,7 @@ describe('optional-services helpers', () => {
       const config: WrapperConfig = {
         ...baseConfig,
         workDir: '/tmp/awf-work',
+        volumeMounts: ['/home/runner:/home/runner:rw'],
       };
 
       const filtered = testHelpers.filterAgentVolumesForSysroot(
@@ -81,11 +82,90 @@ describe('optional-services helpers', () => {
       );
 
       expect(filtered).toEqual([
+        '/home/runner:/host/home/runner:rw',
         '/home/runner/_work/_temp/gh-aw:/host/home/runner/_work/_temp/gh-aw:rw',
         '/tmp:/tmp:rw',
         '/dev/null:/host/home/runner/.npmrc:ro',
         'bad-volume-entry',
       ]);
     });
+
+    it('drops the chroot-home volume but keeps an explicitly mounted writable home', () => {
+      const config: WrapperConfig = {
+        ...baseConfig,
+        workDir: '/tmp/awf-work',
+        volumeMounts: ['/home/runner/_work/_temp/gh-aw/home:/home/runner/_work/_temp/gh-aw/home:rw'],
+      };
+      const home = '/home/runner/_work/_temp/gh-aw/home';
+
+      const filtered = testHelpers.filterAgentVolumesForSysroot(
+        [
+          `/tmp/awf-work-chroot-home:/host${home}:rw`,
+          `${home}:/host${home}:rw`,
+          `/dev/null:/host${home}/.npmrc:ro`,
+          `/dev/null:${home}/.npmrc:ro`,
+        ],
+        config,
+        home,
+      );
+
+      expect(filtered).toEqual([
+        `${home}:/host${home}:rw`,
+        `/dev/null:/host${home}/.npmrc:ro`,
+        `/dev/null:${home}/.npmrc:ro`,
+      ]);
+    });
+
+    it('does not exempt AWF home mounts that merely share a target with an explicit mount', () => {
+      const config: WrapperConfig = {
+        ...baseConfig,
+        workDir: '/tmp/awf-work',
+        volumeMounts: [
+          '/daemon/cache:/home/runner/.cache:rw',
+          '/home/runner/_work/_temp/gh-aw/home:/home/runner:rw',
+        ],
+      };
+
+      const filtered = testHelpers.filterAgentVolumesForSysroot(
+        [
+          '/home/runner/.cache:/host/home/runner/.cache:rw',
+          '/daemon/cache:/host/home/runner/.cache:rw',
+          '/home/runner/_work/_temp/gh-aw/home:/host/home/runner:rw',
+        ],
+        config,
+        '/home/runner',
+      );
+
+      // AWF's own $HOME/.cache bind (runner-side source) is still dropped even
+      // though an explicit mount targets the same path.
+      expect(filtered).toEqual([
+        '/daemon/cache:/host/home/runner/.cache:rw',
+        '/home/runner/_work/_temp/gh-aw/home:/host/home/runner:rw',
+      ]);
+    });
+
+    it('skips /host$HOME credential overlays when no writable /host$HOME survives', () => {
+      const config: WrapperConfig = {
+        ...baseConfig,
+        workDir: '/tmp/awf-work',
+      };
+      const home = '/home/runner/_work/_temp/gh-aw/home';
+
+      const filtered = testHelpers.filterAgentVolumesForSysroot(
+        [
+          `/tmp/awf-work-chroot-home:/host${home}:rw`,
+          `/dev/null:/host${home}/.npmrc:ro`,
+          `/dev/null:${home}/.npmrc:ro`,
+          '/tmp:/tmp:rw',
+        ],
+        config,
+        home,
+      );
+
+      expect(filtered).toEqual([
+        `/dev/null:${home}/.npmrc:ro`,
+        '/tmp:/tmp:rw',
+      ]);
+    });
   });
 });