feat: enhance container environment isolation via credential proxy (#798)

* feat: implement credential proxy for enhanced container environment isolation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: address PR review — bind proxy to loopback, scope OAuth injection, add tests

- Bind credential proxy to 127.0.0.1 instead of 0.0.0.0 (security)
- OAuth mode: only inject Authorization on token exchange endpoint
- Add 5 integration tests for credential-proxy.ts
- Remove dangling comment
- Extract host gateway into container-runtime.ts abstraction
- Update Apple Container skill for credential proxy compatibility

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: scope OAuth token injection by header presence instead of path

Path-based matching missed auth probe requests the CLI sends before
the token exchange. Now the proxy replaces Authorization only when
the container actually sends one, leaving x-api-key-only requests
(post-exchange) untouched.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: bind credential proxy to docker0 bridge IP on Linux

On bare-metal Linux Docker, containers reach the host via the bridge IP
(e.g. 172.17.0.1), not loopback. Detect the docker0 interface address
via os.networkInterfaces() and bind there instead of 0.0.0.0, so the
proxy is reachable by containers but not exposed to the LAN.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: bind credential proxy to loopback on WSL

WSL uses Docker Desktop with the same VM routing as macOS, so
127.0.0.1 is correct and secure. Without this, the fallback to
0.0.0.0 was triggered because WSL has no docker0 interface.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: detect WSL via /proc instead of env var

WSL_DISTRO_NAME isn't set under systemd. Use
/proc/sys/fs/binfmt_misc/WSLInterop which is always present on WSL.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/container-runner.ts

@@ -10,19 +10,22 @@ import {
   CONTAINER_IMAGE,
   CONTAINER_MAX_OUTPUT_SIZE,
   CONTAINER_TIMEOUT,
+  CREDENTIAL_PROXY_PORT,
   DATA_DIR,
   GROUPS_DIR,
   IDLE_TIMEOUT,
   TIMEZONE,
 } from './config.js';
-import { readEnvFile } from './env.js';
 import { resolveGroupFolderPath, resolveGroupIpcPath } from './group-folder.js';
 import { logger } from './logger.js';
 import {
+  CONTAINER_HOST_GATEWAY,
   CONTAINER_RUNTIME_BIN,
+  hostGatewayArgs,
   readonlyMountArgs,
   stopContainer,
 } from './container-runtime.js';
+import { detectAuthMode } from './credential-proxy.js';
 import { validateAdditionalMounts } from './mount-security.js';
 import { RegisteredGroup } from './types.js';
 
@@ -38,7 +41,6 @@ export interface ContainerInput {
   isMain: boolean;
   isScheduledTask?: boolean;
   assistantName?: string;
-  secrets?: Record<string, string>;
 }
 
 export interface ContainerOutput {
@@ -75,7 +77,7 @@ function buildVolumeMounts(
     });
 
     // Shadow .env so the agent cannot read secrets from the mounted project root.
-    // Secrets are passed via stdin instead (see readSecrets()).
+    // Credentials are injected by the credential proxy, never exposed to containers.
     const envFile = path.join(projectRoot, '.env');
     if (fs.existsSync(envFile)) {
       mounts.push({
@@ -210,19 +212,6 @@ function buildVolumeMounts(
   return mounts;
 }
 
-/**
- * Read allowed secrets from .env for passing to the container via stdin.
- * Secrets are never written to disk or mounted as files.
- */
-function readSecrets(): Record<string, string> {
-  return readEnvFile([
-    'CLAUDE_CODE_OAUTH_TOKEN',
-    'ANTHROPIC_API_KEY',
-    'ANTHROPIC_BASE_URL',
-    'ANTHROPIC_AUTH_TOKEN',
-  ]);
-}
-
 function buildContainerArgs(
   mounts: VolumeMount[],
   containerName: string,
@@ -232,6 +221,26 @@ function buildContainerArgs(
   // Pass host timezone so container's local time matches the user's
   args.push('-e', `TZ=${TIMEZONE}`);
 
+  // Route API traffic through the credential proxy (containers never see real secrets)
+  args.push(
+    '-e',
+    `ANTHROPIC_BASE_URL=http://${CONTAINER_HOST_GATEWAY}:${CREDENTIAL_PROXY_PORT}`,
+  );
+
+  // Mirror the host's auth method with a placeholder value.
+  // API key mode: SDK sends x-api-key, proxy replaces with real key.
+  // OAuth mode:   SDK exchanges placeholder token for temp API key,
+  //               proxy injects real OAuth token on that exchange request.
+  const authMode = detectAuthMode();
+  if (authMode === 'api-key') {
+    args.push('-e', 'ANTHROPIC_API_KEY=placeholder');
+  } else {
+    args.push('-e', 'CLAUDE_CODE_OAUTH_TOKEN=placeholder');
+  }
+
+  // Runtime-specific args for host gateway resolution
+  args.push(...hostGatewayArgs());
+
   // Run as host user so bind-mounted files are accessible.
   // Skip when running as root (uid 0), as the container's node user (uid 1000),
   // or when getuid is unavailable (native Windows without WSL).
@@ -309,12 +318,8 @@ export async function runContainerAgent(
     let stdoutTruncated = false;
     let stderrTruncated = false;
 
-    // Pass secrets via stdin (never written to disk or mounted as files)
-    input.secrets = readSecrets();
     container.stdin.write(JSON.stringify(input));
     container.stdin.end();
-    // Remove secrets from input so they don't appear in logs
-    delete input.secrets;
 
     // Streaming output: parse OUTPUT_START/END marker pairs as they arrive
     let parseBuffer = '';