harden sandbox escape vectors for bash disabled/restricted modes (#257)

* harden sandbox escape vectors for bash disabled/restricted modes

block git config injection (-c flag as subcommand), dangerous subcommands
(config, submodule, rebase, bisect), code-executing arg flags (--exec,
--extcmd), .gitattributes/.gitmodules writes, and package lifecycle scripts.
add retry logic to test runner for transient failures. add security unit
tests and adhoc attack tests.

Co-authored-by: Cursor <cursoragent@cursor.com>

* only filter subcommands in nobash, remove nobash from ui

* use regex matching

* iterate on tests

* simplify githooks

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

mcp/dependencies.ts

@@ -1,5 +1,5 @@
 import { type } from "arktype";
-import type { PrepResult } from "../prep/index.ts";
+import type { PrepOptions, PrepResult } from "../prep/index.ts";
 import { runPrepPhase } from "../prep/index.ts";
 import type { ToolContext } from "./server.ts";
 import { execute, tool } from "./shared.ts";
@@ -75,8 +75,14 @@ function startInstallation(ctx: ToolContext): void {
     return;
   }
 
+  // SECURITY: when bash is disabled, suppress lifecycle scripts to prevent
+  // agents from using package.json scripts as a backdoor for code execution
+  const prepOptions: PrepOptions = {
+    ignoreScripts: ctx.payload.bash === "disabled",
+  };
+
   // initialize state and start installation
-  const promise = runPrepPhase();
+  const promise = runPrepPhase(prepOptions);
   ctx.toolState.dependencyInstallation = {
     status: "in_progress",
     promise,