compose: add wrapper-first dogfood workspace (#1488)

Co-authored-by: marcie <[email protected]>

apps/gateway/src/agent/tools/path-guard.ts

@@ -1,47 +1,63 @@
 import path from 'node:path';
 import fs from 'node:fs';
 
-/**
- * Resolves a user-provided path and verifies it is inside the allowed sandbox directory.
- * Throws SandboxEscapeError if the resolved path is outside the sandbox.
- *
- * Uses realpathSync to resolve symlinks in the sandbox root. The user-supplied path
- * is checked for containment AFTER lexical resolution but BEFORE resolving any symlinks
- * within the user path — so symlink escape attempts are caught too.
- *
- * @param userPath - The path provided by the agent (may be relative or absolute)
- * @param sandboxDir - The allowed root directory (already validated on session creation)
- * @returns The resolved absolute path, guaranteed to be within sandboxDir
- */
-export function guardPath(userPath: string, sandboxDir: string): string {
-  const resolved = path.resolve(sandboxDir, userPath);
-  const sandboxResolved = fs.realpathSync.native(sandboxDir);
+function isContained(candidate: string, root: string): boolean {
+  return candidate === root || candidate.startsWith(root + path.sep);
+}
 
-  // Normalize both paths to resolve any symlinks in the sandbox root itself.
-  // For the user path, we check containment BEFORE resolving symlinks in the path
-  // (so we catch symlink escape attempts too — the resolved path must still be under sandbox)
-  if (!resolved.startsWith(sandboxResolved + path.sep) && resolved !== sandboxResolved) {
+function assertLexicalContainment(userPath: string, sandboxDir: string): string {
+  const resolved = path.resolve(sandboxDir, userPath);
+  const sandboxAbsolute = path.resolve(sandboxDir);
+  if (!isContained(resolved, sandboxAbsolute)) {
     throw new SandboxEscapeError(userPath, sandboxDir, resolved);
   }
-
   return resolved;
 }
 
 /**
- * Validates a path without resolving symlinks in the user-provided portion.
- * Use for paths that may not exist yet (creates, writes).
- *
- * Performs a lexical containment check only using path.resolve.
+ * Resolve an existing path and verify both its lexical path and real symlink
+ * target remain inside the sandbox.
+ */
+export function guardPath(userPath: string, sandboxDir: string): string {
+  const resolved = assertLexicalContainment(userPath, sandboxDir);
+  const sandboxReal = fs.realpathSync.native(sandboxDir);
+  const resolvedReal = fs.realpathSync.native(resolved);
+  if (!isContained(resolvedReal, sandboxReal)) {
+    throw new SandboxEscapeError(userPath, sandboxDir, resolvedReal);
+  }
+  return resolvedReal;
+}
+
+/**
+ * Resolve a writable file path whose parent already exists. Existing targets
+ * are resolved fully. New targets use the real parent directory, which blocks
+ * writes through a parent symlink that leaves the sandbox.
+ */
+export function guardWritePath(userPath: string, sandboxDir: string): string {
+  const resolved = assertLexicalContainment(userPath, sandboxDir);
+  const sandboxReal = fs.realpathSync.native(sandboxDir);
+  let writableReal: string;
+  try {
+    writableReal = fs.realpathSync.native(resolved);
+  } catch (error) {
+    const code = (error as NodeJS.ErrnoException).code;
+    if (code !== 'ENOENT') throw error;
+    const parentReal = fs.realpathSync.native(path.dirname(resolved));
+    writableReal = path.join(parentReal, path.basename(resolved));
+  }
+  if (!isContained(writableReal, sandboxReal)) {
+    throw new SandboxEscapeError(userPath, sandboxDir, writableReal);
+  }
+  return writableReal;
+}
+
+/**
+ * Lexical-only validation for non-filesystem pathspecs such as `git diff --`
+ * targets, where the path may name a deleted file and Git does not dereference
+ * a tracked symlink.
  */
 export function guardPathUnsafe(userPath: string, sandboxDir: string): string {
-  const resolved = path.resolve(sandboxDir, userPath);
-  const sandboxAbs = path.resolve(sandboxDir);
-
-  if (!resolved.startsWith(sandboxAbs + path.sep) && resolved !== sandboxAbs) {
-    throw new SandboxEscapeError(userPath, sandboxDir, resolved);
-  }
-
-  return resolved;
+  return assertLexicalContainment(userPath, sandboxDir);
 }
 
 export class SandboxEscapeError extends Error {