feat(gateway): tool path hardening + sandbox escape prevention (P8-016) (#177)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/src/agent/tools/shell-tools.ts

@@ -1,7 +1,7 @@
 import { Type } from '@sinclair/typebox';
 import type { ToolDefinition } from '@mariozechner/pi-coding-agent';
 import { spawn } from 'node:child_process';
-import { resolve, relative } from 'node:path';
+import { guardPath, SandboxEscapeError } from './path-guard.js';
 
 const DEFAULT_TIMEOUT_MS = 30_000;
 const MAX_OUTPUT_BYTES = 100 * 1024; // 100 KB
@@ -68,22 +68,6 @@ function extractBaseCommand(command: string): string {
   return firstToken.split('/').pop() ?? firstToken;
 }
 
-/**
- * Clamp a user-supplied cwd to within the sandbox directory.
- * If the resolved path escapes the sandbox (via ../ or absolute path outside),
- * falls back to the sandbox directory itself.
- */
-function clampCwd(sandboxDir: string, requestedCwd?: string): string {
-  if (!requestedCwd) return sandboxDir;
-  const resolved = resolve(sandboxDir, requestedCwd);
-  const rel = relative(sandboxDir, resolved);
-  if (rel.startsWith('..') || rel.startsWith('/')) {
-    // Escape attempt — fall back to sandbox root
-    return sandboxDir;
-  }
-  return resolved;
-}
-
 function runCommand(
   command: string,
   options: { timeoutMs: number; cwd?: string },
@@ -185,7 +169,21 @@ export function createShellTools(sandboxDir?: string): ToolDefinition[] {
       }
 
       const timeoutMs = Math.min(timeout ?? DEFAULT_TIMEOUT_MS, 60_000);
-      const safeCwd = clampCwd(defaultCwd, cwd);
+      let safeCwd: string;
+      try {
+        safeCwd = guardPath(cwd ?? '.', defaultCwd);
+      } catch (err) {
+        if (err instanceof SandboxEscapeError) {
+          return {
+            content: [{ type: 'text' as const, text: `Error: ${err.message}` }],
+            details: undefined,
+          };
+        }
+        return {
+          content: [{ type: 'text' as const, text: `Error: ${String(err)}` }],
+          details: undefined,
+        };
+      }
 
       const result = await runCommand(command, {
         timeoutMs,