diff --git a/src/config-writer.test.ts b/src/config-writer.test.ts
index 0644f2108..64b21caad 100644
--- a/src/config-writer.test.ts
+++ b/src/config-writer.test.ts
@@ -11,7 +11,7 @@ import * as path from 'path';
 import execa from 'execa';
 import { writeConfigs } from './config-writer';
 import { isOpenSslAvailable } from './ssl-bump';
-import { getRealUserHome } from './host-identity';
+import { getRealUserHome, isNativeRootWithoutSudo } from './host-identity';
 import {
   buildWriteConfig,
   setupConfigWriterTempDir,
@@ -137,6 +137,125 @@ describe('writeConfigs', () => {
       );
     });
 
+    it('chowns the host workspace on native-root runners', async () => {
+      Object.defineProperty(process, 'getuid', { value: () => 0, configurable: true });
+      (isNativeRootWithoutSudo as jest.Mock).mockReturnValue(true);
+      const workspaceDir = path.join(tempDir, 'workspace');
+      process.env.GITHUB_WORKSPACE = workspaceDir;
+      fs.mkdirSync(workspaceDir, { recursive: true });
+      fs.chmodSync(workspaceDir, 0o777);
+
+      await writeConfigs(buildWriteConfig(tempDir, { containerWorkDir: workspaceDir }));
+
+      expect(execa.sync).toHaveBeenCalledWith(
+        'chown',
+        ['-h', '-P', '-R', '--', '1000:1000', workspaceDir],
+        expect.objectContaining({ reject: false })
+      );
+    });
+
+    it('chowns the host workspace when the container workdir is beneath it', async () => {
+      Object.defineProperty(process, 'getuid', { value: () => 0, configurable: true });
+      (isNativeRootWithoutSudo as jest.Mock).mockReturnValue(true);
+      const workspaceDir = path.join(tempDir, 'workspace');
+      const containerWorkDir = path.join(workspaceDir, 'packages', 'app');
+      process.env.GITHUB_WORKSPACE = workspaceDir;
+      fs.mkdirSync(containerWorkDir, { recursive: true });
+      fs.chmodSync(workspaceDir, 0o777);
+
+      await writeConfigs(buildWriteConfig(tempDir, { containerWorkDir }));
+
+      expect(execa.sync).toHaveBeenCalledWith(
+        'chown',
+        ['-h', '-P', '-R', '--', '1000:1000', workspaceDir],
+        expect.objectContaining({ reject: false })
+      );
+    });
+
+    it('throws when the host workspace stays unwritable by the sandbox identity', async () => {
+      Object.defineProperty(process, 'getuid', { value: () => 0, configurable: true });
+      (isNativeRootWithoutSudo as jest.Mock).mockReturnValue(true);
+      const workspaceDir = path.join(tempDir, 'workspace');
+      process.env.GITHUB_WORKSPACE = workspaceDir;
+      fs.mkdirSync(workspaceDir, { recursive: true });
+      fs.chmodSync(workspaceDir, 0o755);
+
+      await expect(
+        writeConfigs(buildWriteConfig(tempDir, { containerWorkDir: workspaceDir }))
+      ).rejects.toThrow(
+        `Host workspace is not writable by the sandbox identity (1000:1000): ${workspaceDir}`
+      );
+    });
+
+    it.each(['/tmp', '/etc', '/'])(
+      'does not chown an unrelated custom container workdir (%s)',
+      async containerWorkDir => {
+        Object.defineProperty(process, 'getuid', { value: () => 0, configurable: true });
+        (isNativeRootWithoutSudo as jest.Mock).mockReturnValue(true);
+        const workspaceDir = path.join(tempDir, 'workspace');
+        process.env.GITHUB_WORKSPACE = workspaceDir;
+        fs.mkdirSync(workspaceDir, { recursive: true });
+
+        await writeConfigs(buildWriteConfig(tempDir, { containerWorkDir }));
+
+        expect(execa.sync).not.toHaveBeenCalledWith(
+          'chown',
+          expect.arrayContaining([containerWorkDir]),
+          expect.anything()
+        );
+      }
+    );
+
+    it('rejects a filesystem root as the host workspace', async () => {
+      Object.defineProperty(process, 'getuid', { value: () => 0, configurable: true });
+      (isNativeRootWithoutSudo as jest.Mock).mockReturnValue(true);
+      process.env.GITHUB_WORKSPACE = '/';
+
+      await expect(
+        writeConfigs(buildWriteConfig(tempDir, { containerWorkDir: '/' }))
+      ).rejects.toThrow('Refusing to repair ownership of filesystem root: /');
+
+      expect(execa.sync).not.toHaveBeenCalledWith(
+        'chown',
+        expect.arrayContaining(['/']),
+        expect.anything()
+      );
+    });
+
+    it('rejects a host workspace symlink that resolves to a filesystem root', async () => {
+      Object.defineProperty(process, 'getuid', { value: () => 0, configurable: true });
+      (isNativeRootWithoutSudo as jest.Mock).mockReturnValue(true);
+      const workspaceDir = path.join(tempDir, 'workspace-root');
+      fs.symlinkSync('/', workspaceDir);
+      process.env.GITHUB_WORKSPACE = workspaceDir;
+
+      await expect(
+        writeConfigs(buildWriteConfig(tempDir, { containerWorkDir: workspaceDir }))
+      ).rejects.toThrow('Refusing to repair ownership of filesystem root: /');
+
+      expect(execa.sync).not.toHaveBeenCalledWith(
+        'chown',
+        expect.arrayContaining(['/']),
+        expect.anything()
+      );
+    });
+
+    it('does not touch the host workspace when not running as native root', async () => {
+      (isNativeRootWithoutSudo as jest.Mock).mockReturnValue(false);
+      const workspaceDir = path.join(tempDir, 'workspace');
+      process.env.GITHUB_WORKSPACE = workspaceDir;
+      fs.mkdirSync(workspaceDir, { recursive: true });
+      fs.chmodSync(workspaceDir, 0o755);
+
+      await writeConfigs(buildWriteConfig(tempDir, { containerWorkDir: workspaceDir }));
+
+      expect(execa.sync).not.toHaveBeenCalledWith(
+        'chown',
+        ['-h', '-P', '-R', '--', '1000:1000', workspaceDir],
+        expect.anything()
+      );
+    });
+
     it('throws when workDir path exists but is not a directory', async () => {
       const filePath = path.join(tempDir, 'not-a-directory');
       fs.writeFileSync(filePath, 'content');
diff --git a/src/config-writer.ts b/src/config-writer.ts
index e5ba8b3ab..a79e78f0b 100644
--- a/src/config-writer.ts
+++ b/src/config-writer.ts
@@ -13,7 +13,7 @@ import { generateDockerCompose, redactDockerComposeSecrets } from './compose-gen
 import { deriveSensitiveEndpointForms, redactSensitiveValues } from './redact-secrets';
 import { resolveLogPaths } from './log-paths';
 import { DEFAULT_DNS_SERVERS, filterForNetworkIsolation } from './dns-resolver';
-import { getSafeHostGid, getSafeHostUid } from './host-identity';
+import { getSafeHostGid, getSafeHostUid, isNativeRootWithoutSudo } from './host-identity';
 import {
   AGENT_IP,
   API_PROXY_IP,
@@ -104,6 +104,33 @@ function chownTreeWithoutFollowingSymlink(targetPath: string, uid: number, gid:
   }
 }
 
+/**
+ * Resolves the sandbox identity used inside the agent container, or null when
+ * it is not a usable unprivileged identity.
+ */
+function resolveSandboxIdentity(): { uid: number; gid: number } | null {
+  const uid = Number.parseInt(getSafeHostUid(), 10);
+  const gid = Number.parseInt(getSafeHostGid(), 10);
+  if (!Number.isInteger(uid) || !Number.isInteger(gid) || uid <= 0 || gid <= 0) {
+    return null;
+  }
+  return { uid, gid };
+}
+
+/**
+ * Transfers ownership of a host path to the sandbox identity, logging (rather
+ * than throwing) when the repair cannot be completed.
+ */
+function repairPathOwnership(targetPath: string, uid: number, gid: number): void {
+  try {
+    chownTreeWithoutFollowingSymlink(targetPath, uid, gid);
+    logger.debug(`Transferred ${targetPath} ownership to sandbox user (${uid}:${gid}) before container launch`);
+  } catch (error) {
+    const message = error instanceof Error ? error.message : String(error);
+    logger.warn(`Failed to transfer ${targetPath} ownership to sandbox user (${uid}:${gid}): ${message}`);
+  }
+}
+
 function repairRunnerTempGhAwOwnership(): void {
   if (process.getuid?.() !== 0) {
     return;
@@ -119,19 +146,110 @@ function repairRunnerTempGhAwOwnership(): void {
     return;
   }
 
-  const uid = Number.parseInt(getSafeHostUid(), 10);
-  const gid = Number.parseInt(getSafeHostGid(), 10);
-  if (!Number.isInteger(uid) || !Number.isInteger(gid) || uid <= 0 || gid <= 0) {
+  const identity = resolveSandboxIdentity();
+  if (!identity) {
     logger.warn(`Skipping ${ghAwRoot} ownership repair because the sandbox identity is invalid`);
     return;
   }
 
+  repairPathOwnership(ghAwRoot, identity.uid, identity.gid);
+}
+
+/**
+ * Reports whether the sandbox identity can create entries in `targetDir`.
+ *
+ * The host process usually runs as root, which bypasses permission checks, so
+ * `fs.accessSync` cannot answer this question. The mode bits are inspected
+ * directly instead: the sandbox identity has no supplementary groups inside the
+ * container, so owner/group/other is the complete picture.
+ */
+function isDirectoryWritableByIdentity(targetDir: string, uid: number, gid: number): boolean {
+  let stat: fs.Stats;
   try {
-    chownTreeWithoutFollowingSymlink(ghAwRoot, uid, gid);
-    logger.debug(`Transferred ${ghAwRoot} ownership to sandbox user (${uid}:${gid}) before container launch`);
-  } catch (error) {
-    const message = error instanceof Error ? error.message : String(error);
-    logger.warn(`Failed to transfer ${ghAwRoot} ownership to sandbox user (${uid}:${gid}): ${message}`);
+    stat = fs.statSync(targetDir);
+  } catch {
+    return false;
+  }
+
+  if (!stat.isDirectory()) {
+    return false;
+  }
+
+  // Write + search permission are both required to create entries in a directory.
+  if (stat.uid === uid) {
+    return (stat.mode & 0o300) === 0o300;
+  }
+  if (stat.gid === gid) {
+    return (stat.mode & 0o030) === 0o030;
+  }
+  return (stat.mode & 0o003) === 0o003;
+}
+
+/**
+ * Repairs ownership of the host workspace mount and verifies the sandbox
+ * identity can write to it.
+ *
+ * On native-root runners (root with no `SUDO_UID`, e.g. AWS CodeBuild-hosted
+ * runners) the checkout is root-owned while the agent runs as the fallback
+ * sandbox identity, so the workdir is writable by mount but not by ownership.
+ * Without this repair the agent silently fails to write and the job reports a
+ * false green.
+ */
+function repairContainerWorkDirOwnership(config: WrapperConfig): void {
+  const containerWorkDir = config.containerWorkDir;
+  if (!containerWorkDir || !path.isAbsolute(containerWorkDir)) {
+    return;
+  }
+
+  if (!isNativeRootWithoutSudo()) {
+    return;
+  }
+
+  const workspaceDir = process.env.GITHUB_WORKSPACE || process.cwd();
+  if (!path.isAbsolute(workspaceDir)) {
+    return;
+  }
+
+  const normalizedWorkspaceDir = path.resolve(workspaceDir);
+  const normalizedContainerWorkDir = path.resolve(containerWorkDir);
+  const relativeWorkDir = path.relative(normalizedWorkspaceDir, normalizedContainerWorkDir);
+  const workDirUsesWorkspaceMount =
+    relativeWorkDir === '' ||
+    (relativeWorkDir !== '..' &&
+      !relativeWorkDir.startsWith(`..${path.sep}`) &&
+      !path.isAbsolute(relativeWorkDir));
+  if (!workDirUsesWorkspaceMount) {
+    return;
+  }
+
+  if (!fs.existsSync(normalizedWorkspaceDir)) {
+    return;
+  }
+
+  const canonicalWorkspaceDir = fs.realpathSync(normalizedWorkspaceDir);
+  if (canonicalWorkspaceDir === path.parse(canonicalWorkspaceDir).root) {
+    throw new Error(`Refusing to repair ownership of filesystem root: ${canonicalWorkspaceDir}`);
+  }
+
+  const identity = resolveSandboxIdentity();
+  if (!identity) {
+    logger.warn(`Skipping ${canonicalWorkspaceDir} ownership repair because the sandbox identity is invalid`);
+    return;
+  }
+
+  repairPathOwnership(canonicalWorkspaceDir, identity.uid, identity.gid);
+
+  if (!isDirectoryWritableByIdentity(canonicalWorkspaceDir, identity.uid, identity.gid)) {
+    throw new Error(
+      `Host workspace is not writable by the sandbox identity ` +
+      `(${identity.uid}:${identity.gid}): ${canonicalWorkspaceDir}\n` +
+      `AWF is running as root without SUDO_UID, so it attempted to transfer ` +
+      `ownership of the host workspace to the sandbox identity, but the ` +
+      `workspace is still not writable.\n` +
+      `The agent would start and exit successfully without being able to write ` +
+      `any files, so AWF is failing early instead.\n` +
+      `  Suggested fix: chown -R ${identity.uid}:${identity.gid} ${canonicalWorkspaceDir} before invoking AWF.`
+    );
   }
 }
 
@@ -386,6 +504,7 @@ export async function writeConfigs(config: WrapperConfig): Promise<void> {
   const logPaths = resolveLogPaths(config);
   prepareWorkDirectories(config, logPaths);
   repairRunnerTempGhAwOwnership();
+  repairContainerWorkDirOwnership(config);
 
   // Use fixed network configuration (network is created by host-iptables.ts)
   const networkConfig: NetworkConfig = {